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Re: [SCA-Archery] poundage question

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  • Siegfried Sebastian Faust
    ... While you are right that the length of the draw changes the poundage Carolus ... the brace height will ALSO do that. If you shorten your string to have a
    Message 1 of 24 , Apr 1 1:39 PM
      At 01:49 PM 4/1/2004, Carolus Eulenhorst wrote:
      >No. The poundage is determined by the length of the draw, not the brace
      >height.

      While you are right that the length of the draw changes the poundage
      Carolus ... the brace height will ALSO do that.

      If you shorten your string to have a higher brace height, the limbs are
      more flexed because of the shorter string, when you pull it to the same
      point, the limbs will be even more flexed that they would have been with
      the longer string, and therefore the poundage will have increased.

      However, with the longer brace height, you will have a shorter power
      stroke, therefore robbing energy.

      I, and others, use this effect all the time on combat crossbows to 'tune'
      them to be around the 600 in-lb mark ... loosen the string to drop poundage
      but increase power stroke, shorten the string to up poundage and lose power
      stroke.

      It isn't a linear curve, and therefore you can often adjust (for combat
      archery) an 'illegal' 625 in-lb crossbow to be a legal 600 in-lb crossbow
      through these adjustments.

      Siegfried



      ___________________________________________________________________________
      THL Siegfried Sebastian Faust http://crossbows.biz/
      Barony of Highland Foorde Baronial Web Minister & Archery Marshal
      Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
      http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
    • atruemark@aol.com
      In a message dated 4/1/04 1:46:03 PM Pacific Standard Time, crossbow@freeshell.org writes: If you shorten your string to have a higher brace height, the limbs
      Message 2 of 24 , Apr 1 3:00 PM
        In a message dated 4/1/04 1:46:03 PM Pacific Standard Time,
        crossbow@... writes:
        If you shorten your string to have a higher brace height, the limbs are
        more flexed because of the shorter string, when you pull it to the same
        point, the limbs will be even more flexed that they would have been with
        the longer string, and therefore the poundage will have increased.

        However, with the longer brace height, you will have a shorter power
        stroke, therefore robbing energy.

        I, and others, use this effect all the time on combat crossbows to 'tune'
        them to be around the 600 in-lb mark ... loosen the string to drop poundage
        but increase power stroke, shorten the string to up poundage and lose power
        stroke.

        It isn't a linear curve, and therefore you can often adjust (for combat
        archery) an 'illegal' 625 in-lb crossbow to be a legal 600 in-lb crossbow
        through these adjustments.

        Siegfried

        This is one of those subjects in archery where everyone is saying the same
        thing, but using different terminology to describe the effect. In this case, I
        believe Carolus to be correct.

        Think of it this way. Imagine your bow as being perfectly straight from
        riser to limb tip. Now brace it to 6". It will have stored "X" amount of energy
        in the limbs. Draw it back to your anchor point and it will have "X" amount
        of more stored energy in the limb. Now twist the string up a bit and increase
        the brace height to 7". Have you "increased the poundage?" No. All you've
        done is increase the stored energy in the limb for that increased brace height.
        If you draw back to your regular anchor, you are still storing the same
        amount of energy as you would have with a 6" brace height.

        What is different is the amount of time the string is in contact with the
        arrow, which is what fools a lot of folks. The lower the brace height (within
        good operating parameters for the style of bow) the more of the stored energy
        makes it into the arrow, increasing arrow speed off the bow. The higher the
        brace height, the less time the string is in contact with the arrow, slowing the
        arrow speed. These differences can be quite dramatic and allow the shooter to
        fine tune for things like over/under spine in the bow and arrow relationship.

        Again, the net effect is the same as both of you have described it, but the
        mechanism for getting there is as described above. The poundage does not
        change, per se, but the amount of energy transferal increases and decreases
        according to brace height.

        Regards,

        Andras Truemark


        [Non-text portions of this message have been removed]
      • georgeledbury@aol.com
        NO [Non-text portions of this message have been removed]
        Message 3 of 24 , Apr 1 6:22 PM
          NO


          [Non-text portions of this message have been removed]
        • Carl West
          ... Same amount of available energy? maybe. Different draw weight? maybe. Different geometry? certainly. Someone with a bow-scale, a measuring tape, graph
          Message 4 of 24 , Apr 1 9:12 PM
            atruemark@... wrote:
            >
            > In a message dated 4/1/04 1:46:03 PM Pacific Standard Time,
            > crossbow@... writes:
            > > If you shorten your string to have a higher brace height, the limbs are
            > > more flexed because of the shorter string, when you pull it to the same
            > > point, the limbs will be even more flexed that they would have been with
            > > the longer string, and therefore the poundage will have increased.



            > Think of it this way. Imagine your bow as being perfectly straight from
            > riser to limb tip. Now brace it to 6". It will have stored "X" amount of energy
            > in the limbs. Draw it back to your anchor point and it will have "X" amount
            > of more stored energy in the limb. Now twist the string up a bit and increase
            > the brace height to 7". Have you "increased the poundage?" No. All you've
            > done is increase the stored energy in the limb for that increased brace height.
            > If you draw back to your regular anchor, you are still storing the same
            > amount of energy as you would have with a 6" brace height.


            Same amount of available energy? maybe.
            Different draw weight? maybe.
            Different geometry? certainly.

            Someone with a bow-scale, a measuring tape, graph paper, a bow and a little time want to make a chart or two?

            This guy addresses some of the issues, but doesn't speak to the question of draw-weight v. brace-height:
            http://homepage.ntlworld.com/joetapley/bh.htm
            nor does he give any citations of of authorities or research.
            There's no proof that he didn't develop this through rectal extraction.

            He certainly has a lot of stuff on archery on his site. Trim the URL to see. Not all of what he says makes sense to me, but, it's late.

            -- Fritz


            If you try to 'reply' to me without fixing the dot, your reply
            will go into a 'special' mailbox reserved for spam. See below.


            --
            Carl West carlDOTwest@... http://carl.west.home.comcast.net

            >>>>>>>> change the 'DOT' to '.' to email me <<<<<<<<<<<<

            "Clutter"? This is an object-rich environment.
          • atruemark@aol.com
            I agree with Carl that my earlier explanation was simplistic. It s also true, in the same way that saying a chunk of lead is solid, which it is in a real
            Message 5 of 24 , Apr 1 11:22 PM
              I agree with Carl that my earlier explanation was simplistic. It's also
              true, in the same way that saying a chunk of lead is solid, which it is in a real
              world kind of way. On an atomic level, however, it isn't - in fact, it's full
              of space and in no way a solid. So to with brace height vs poundage. My
              earlier explanation is true, in a general, real world sense. Technically,
              however, all sorts of factors come into play - bow profile, materials, even the mass
              of the string. This is from Archery; The Technical Side, of the Legends of
              the Longbow series compiled by Glenn St. Charles, in an article written in
              March 1931 by C.N. Hickman.

              "This means that a bow braced high does not require much more strength to
              hold, when fully drawn, than if it were braced low....and for all practical
              bracing heights, the force-draw curves merge into one common curve near the end
              of a full draw." (page 19, paragraph 5). Further, "The drawing force for a
              full draw is almost independent of the bracing height of the bow string."
              (page 21, first point under Summary) and "The arrow velocity increases with
              increase in bracing height up to a certain point (if starting with zero brace
              height), after which it slowly decreases with additional increases in bracing
              height." (page 21, point 5 under Summary).

              So, without taking into account a variety of factors, it is safe to say that
              the major impact that lowering or raising brace height has on performance is
              not poundage related, but more in how long the string stays in contact with the
              arrow, thus transfering stored energy into the arrow.

              Regards,

              Andras Truemark


              [Non-text portions of this message have been removed]
            • Carolus Eulenhorst
              I don t find this at all. Testing three crossbows and four recurves (three working recurves and one semi-working recurve), I find the poundage the same at the
              Message 6 of 24 , Apr 1 11:50 PM
                I don't find this at all. Testing three crossbows and four recurves
                (three working recurves and one semi-working recurve), I find the
                poundage the same at the same draw length regardless of where I have the
                brace height..The bow is flexed the same amount at the same draw length
                though it is, indeed, flexed more at rest with a higher brace height. In
                forty years of shooting I have never found changing the brace height to
                change the total draw weight.

                The effect you see is not the result of poundage change but rather
                distance change. For example, a crossbow braced at 4 inches and drawn 10
                inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                pull. If the brace height is raised to 4.4 inches it reduces the draw
                length to 9.6 inches. When multiplied against the same 62.5 pound pull
                the result is 600 inch pounds. This is what has led to many
                misunderstandings about the power of crossbows on the combat field. Some
                would say that a 62.5 pound crossbow in too powerful but they are
                ignoring the fact that the power curve is reduced and thus the work done
                on the bolt is decreased resulting in less impact.

                If you do actually see the poundage change I would like more information
                on the poundages at each brace height, draw lengths, and construction of
                the bows.
                Carolus
                On Thu, 01 Apr 2004 16:39:14 -0500 Siegfried Sebastian Faust
                <crossbow@...> writes:
                > At 01:49 PM 4/1/2004, Carolus Eulenhorst wrote:
                > >No. The poundage is determined by the length of the draw, not the
                > brace
                > >height.
                >
                > While you are right that the length of the draw changes the poundage
                >
                > Carolus ... the brace height will ALSO do that.
                >
                > If you shorten your string to have a higher brace height, the limbs
                > are
                > more flexed because of the shorter string, when you pull it to the
                > same
                > point, the limbs will be even more flexed that they would have been
                > with
                > the longer string, and therefore the poundage will have increased.
                >
                > However, with the longer brace height, you will have a shorter power
                >
                > stroke, therefore robbing energy.
                >
                > I, and others, use this effect all the time on combat crossbows to
                > 'tune'
                > them to be around the 600 in-lb mark ... loosen the string to drop
                > poundage
                > but increase power stroke, shorten the string to up poundage and
                > lose power
                > stroke.
                >
                > It isn't a linear curve, and therefore you can often adjust (for
                > combat
                > archery) an 'illegal' 625 in-lb crossbow to be a legal 600 in-lb
                > crossbow
                > through these adjustments.
                >
                > Siegfried

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              • Siegfried Sebastian Faust
                Ok Carolus, I see a slight error here, and I want to try to explain this, if the explantion doesn t work, I ll draw a graphic ... just let me know. I find the
                Message 7 of 24 , Apr 2 7:26 AM
                  Ok Carolus, I see a slight error here, and I want to try to explain this,
                  if the explantion doesn't work, I'll draw a graphic ... just let me know.

                  I find the
                  >poundage the same at the same draw length regardless of where I have the
                  >brace height..The bow is flexed the same amount at the same draw length
                  >though it is, indeed, flexed more at rest with a higher brace height.
                  [snip]
                  >The effect you see is not the result of poundage change but rather
                  >distance change. For example, a crossbow braced at 4 inches and drawn 10
                  >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                  >pull. If the brace height is raised to 4.4 inches it reduces the draw
                  >length to 9.6 inches. When multiplied against the same 62.5 pound pull
                  >the result is 600 inch pounds.
                  [snip]
                  >If you do actually see the poundage change I would like more information
                  >on the poundages at each brace height, draw lengths, and construction of
                  >the bows.

                  Ok Carolus, simple physics ... and I'm going to use crossbows as an
                  example, just because I find it a better mental model.

                  Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
                  string. That gives you some amount of brace height.

                  Ok, now imagine the crossbow drawn back and cocked. Assume now, that
                  there is a 1" wide nut/shelf/etc it is in.

                  If you measure the length now, of the string on either side of the nut to
                  the tip. You will find it is 12.5" ... half the width of the string, after
                  the 1" of nut is taken into consideration. So the angle the prod is being
                  held at, is to allow for a 12.5" length of string on either side of it to
                  exist. Measure the poundage here.

                  Ok, now, take the string off and twist it tighter until it is only 25" long.

                  Ok, now put it back on the crossbow, and you will have a higher brace
                  height. Agreed?

                  So now, pull back/cock the crossbow. Do the same measurements. Now, there
                  is only 12" on either side of string. By simple physics, the prod has been
                  pulled back farther. There is no other way around it. Now, unless this
                  prod 'somehow' has magical properties that give it a smooth unchanging
                  poundage (I know of none), the fact that it is being stressed farther,
                  means it took more force to get it there, and therefore, if you put a
                  bowscale on it now, the poundage will be higher.

                  Now, as stated, the power stroke is now shorter, as the string stops
                  sooner, and this counteracts 'somewhat' the difference. However, each bow
                  is different, and some stringheight/poundage is the optimum for that
                  bow/prod, others are less efficient, therefore, depending upon the bow, you
                  can adjust it's poundage, and it's power, by playing with that, because in
                  my experience, it isn't a smooth curve.

                  Siegfried
                  (Who will also sit down and do lots of string pulling on one of his
                  crossbows for ya if he has to *grin*)



                  ___________________________________________________________________________
                  THL Siegfried Sebastian Faust http://crossbows.biz/
                  Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                  Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                  http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                • eulenhorst@juno.com
                  No. The pre-stress is higher but the total stress is identical. A spring tensioned to the same point will only show a certain poundage regardless of the
                  Message 8 of 24 , Apr 2 2:16 PM
                    No. The pre-stress is higher but the total stress is identical. A spring tensioned to the same point will only show a certain poundage regardless of the prestress. The archery mechanics site posted earlier has a good discussion of spring loading and prestress under plunger buttons. My results are empirical based on actual tests with a bow scale, not theoretical.

                    In Service to the dream
                    Carolus von Eulenhorst
                    eulenhorst@...
                    BTW, that mechanics site has some references on the home page and seems well grounded.
                    CvE

                    -- Siegfried Sebastian Faust <crossbow@...> wrote:
                    Ok Carolus, I see a slight error here, and I want to try to explain this,
                    if the explantion doesn't work, I'll draw a graphic ... just let me know.

                    I find the
                    >poundage the same at the same draw length regardless of where I have the
                    >brace height..The bow is flexed the same amount at the same draw length
                    >though it is, indeed, flexed more at rest with a higher brace height.
                    [snip]
                    >The effect you see is not the result of poundage change but rather
                    >distance change. For example, a crossbow braced at 4 inches and drawn 10
                    >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                    >pull. If the brace height is raised to 4.4 inches it reduces the draw
                    >length to 9.6 inches. When multiplied against the same 62.5 pound pull
                    >the result is 600 inch pounds.
                    [snip]
                    >If you do actually see the poundage change I would like more information
                    >on the poundages at each brace height, draw lengths, and construction of
                    >the bows.

                    Ok Carolus, simple physics ... and I'm going to use crossbows as an
                    example, just because I find it a better mental model.

                    Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
                    string. That gives you some amount of brace height.

                    Ok, now imagine the crossbow drawn back and cocked. Assume now, that
                    there is a 1" wide nut/shelf/etc it is in.

                    If you measure the length now, of the string on either side of the nut to
                    the tip. You will find it is 12.5" ... half the width of the string, after
                    the 1" of nut is taken into consideration. So the angle the prod is being
                    held at, is to allow for a 12.5" length of string on either side of it to
                    exist. Measure the poundage here.

                    Ok, now, take the string off and twist it tighter until it is only 25" long.

                    Ok, now put it back on the crossbow, and you will have a higher brace
                    height. Agreed?

                    So now, pull back/cock the crossbow. Do the same measurements. Now, there
                    is only 12" on either side of string. By simple physics, the prod has been
                    pulled back farther. There is no other way around it. Now, unless this
                    prod 'somehow' has magical properties that give it a smooth unchanging
                    poundage (I know of none), the fact that it is being stressed farther,
                    means it took more force to get it there, and therefore, if you put a
                    bowscale on it now, the poundage will be higher.

                    Now, as stated, the power stroke is now shorter, as the string stops
                    sooner, and this counteracts 'somewhat' the difference. However, each bow
                    is different, and some stringheight/poundage is the optimum for that
                    bow/prod, others are less efficient, therefore, depending upon the bow, you
                    can adjust it's poundage, and it's power, by playing with that, because in
                    my experience, it isn't a smooth curve.

                    Siegfried
                    (Who will also sit down and do lots of string pulling on one of his
                    crossbows for ya if he has to *grin*)



                    ___________________________________________________________________________
                    THL Siegfried Sebastian Faust http://crossbows.biz/
                    Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                    Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                    http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/



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                  • Scott Jaqua
                    Actually Carolus, as a logic thought problem, I come up with more total stress too. Lower brace height equals a shorter string. A sorter string at the same
                    Message 9 of 24 , Apr 2 2:45 PM
                      Actually Carolus, as a logic thought problem, I come up with more total
                      stress too. Lower brace height equals a shorter string. A sorter string at
                      the same draw length means the tip of the limb had to flex further. And thus
                      more total stress. But I can't tell you if this is one of the cases where
                      the real world observations don't match theory.

                      Njall
                      (jr rocket scientist, for a real rocket scientist, talk to my dad)

                      Scott B. Jaqua
                      ----------------------------------------------------------------------------
                      -----------------------------
                      The most import right of all, is that of free speech. Without that, all your
                      other rights will soon be taken away. So, I may disagree with what you say,
                      but I will defend until death, your right to say it!
                      ----- Original Message -----
                      From: <eulenhorst@...>
                      To: <SCA-Archery@yahoogroups.com>
                      Sent: Friday, April 02, 2004 2:16 PM
                      Subject: Re: [SCA-Archery] poundage question


                      >
                      > No. The pre-stress is higher but the total stress is identical. A spring
                      tensioned to the same point will only show a certain poundage regardless of
                      the prestress. The archery mechanics site posted earlier has a good
                      discussion of spring loading and prestress under plunger buttons. My
                      results are empirical based on actual tests with a bow scale, not
                      theoretical.
                      >
                      > In Service to the dream
                      > Carolus von Eulenhorst
                      > eulenhorst@...
                      > BTW, that mechanics site has some references on the home page and seems
                      well grounded.
                      > CvE
                      >
                      > -- Siegfried Sebastian Faust <crossbow@...> wrote:
                      > Ok Carolus, I see a slight error here, and I want to try to explain this,
                      > if the explantion doesn't work, I'll draw a graphic ... just let me know.
                      >
                      > I find the
                      > >poundage the same at the same draw length regardless of where I have the
                      > >brace height..The bow is flexed the same amount at the same draw length
                      > >though it is, indeed, flexed more at rest with a higher brace height.
                      > [snip]
                      > >The effect you see is not the result of poundage change but rather
                      > >distance change. For example, a crossbow braced at 4 inches and drawn 10
                      > >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                      > >pull. If the brace height is raised to 4.4 inches it reduces the draw
                      > >length to 9.6 inches. When multiplied against the same 62.5 pound pull
                      > >the result is 600 inch pounds.
                      > [snip]
                      > >If you do actually see the poundage change I would like more information
                      > >on the poundages at each brace height, draw lengths, and construction of
                      > >the bows.
                      >
                      > Ok Carolus, simple physics ... and I'm going to use crossbows as an
                      > example, just because I find it a better mental model.
                      >
                      > Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
                      > string. That gives you some amount of brace height.
                      >
                      > Ok, now imagine the crossbow drawn back and cocked. Assume now, that
                      > there is a 1" wide nut/shelf/etc it is in.
                      >
                      > If you measure the length now, of the string on either side of the nut to
                      > the tip. You will find it is 12.5" ... half the width of the string,
                      after
                      > the 1" of nut is taken into consideration. So the angle the prod is being
                      > held at, is to allow for a 12.5" length of string on either side of it to
                      > exist. Measure the poundage here.
                      >
                      > Ok, now, take the string off and twist it tighter until it is only 25"
                      long.
                      >
                      > Ok, now put it back on the crossbow, and you will have a higher brace
                      > height. Agreed?
                      >
                      > So now, pull back/cock the crossbow. Do the same measurements. Now,
                      there
                      > is only 12" on either side of string. By simple physics, the prod has
                      been
                      > pulled back farther. There is no other way around it. Now, unless this
                      > prod 'somehow' has magical properties that give it a smooth unchanging
                      > poundage (I know of none), the fact that it is being stressed farther,
                      > means it took more force to get it there, and therefore, if you put a
                      > bowscale on it now, the poundage will be higher.
                      >
                      > Now, as stated, the power stroke is now shorter, as the string stops
                      > sooner, and this counteracts 'somewhat' the difference. However, each
                      bow
                      > is different, and some stringheight/poundage is the optimum for that
                      > bow/prod, others are less efficient, therefore, depending upon the bow,
                      you
                      > can adjust it's poundage, and it's power, by playing with that, because in
                      > my experience, it isn't a smooth curve.
                      >
                      > Siegfried
                      > (Who will also sit down and do lots of string pulling on one of his
                      > crossbows for ya if he has to *grin*)
                      >
                      >
                      >
                      >
                      ___________________________________________________________________________
                      > THL Siegfried Sebastian Faust
                      http://crossbows.biz/
                      > Barony of Highland Foorde Baronial Web Minister & Archery
                      Marshal
                      > Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target
                      Archery
                      > http://highland-foorde.atlantia.sca.org/
                      http://archery.atlantia.sca.org/
                      >
                      >
                      >
                      > ---8<---------------------------------------------
                      > Brought to you YahooGroups Ad Free in 2003 by Medieval Mart
                      > Get Medieval at Mad Macsen's http://www.medievalmart.com/
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                      >
                      > Yahoo! Groups Links
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                    • eulenhorst@juno.com
                      This only works if the draw distance remains constant thus resulting in more draw with the higher brace height. If the bow is drawn to 28 , for example, it
                      Message 10 of 24 , Apr 2 3:28 PM
                        This only works if the draw distance remains constant thus resulting in more draw with the higher brace height. If the bow is drawn to 28", for example, it doesn't matter if it started with a brace of 7" or 8". The draw length in the first case is 21" and in the second 20". If, however we use a draw distance of 20" we get a draw length of 27" with a 7" brace and 28" with an 8" brace. In this case the draw weight does change.


                        In Service to the dream
                        Carolus von Eulenhorst
                        eulenhorst@...

                        -- "Scott Jaqua" <jaqua@...> wrote:
                        Actually Carolus, as a logic thought problem, I come up with more total
                        stress too. Lower brace height equals a shorter string. A sorter string at
                        the same draw length means the tip of the limb had to flex further. And thus
                        more total stress. But I can't tell you if this is one of the cases where
                        the real world observations don't match theory.

                        Njall
                        (jr rocket scientist, for a real rocket scientist, talk to my dad)

                        Scott B. Jaqua
                        ----------------------------------------------------------------------------
                        -----------------------------
                        The most import right of all, is that of free speech. Without that, all your
                        other rights will soon be taken away. So, I may disagree with what you say,
                        but I will defend until death, your right to say it!
                        ----- Original Message -----
                        From: <eulenhorst@...>
                        To: <SCA-Archery@yahoogroups.com>
                        Sent: Friday, April 02, 2004 2:16 PM
                        Subject: Re: [SCA-Archery] poundage question


                        >
                        > No. The pre-stress is higher but the total stress is identical. A spring
                        tensioned to the same point will only show a certain poundage regardless of
                        the prestress. The archery mechanics site posted earlier has a good
                        discussion of spring loading and prestress under plunger buttons. My
                        results are empirical based on actual tests with a bow scale, not
                        theoretical.
                        >
                        > In Service to the dream
                        > Carolus von Eulenhorst
                        > eulenhorst@...
                        > BTW, that mechanics site has some references on the home page and seems
                        well grounded.
                        > CvE
                        >
                        > -- Siegfried Sebastian Faust <crossbow@...> wrote:
                        > Ok Carolus, I see a slight error here, and I want to try to explain this,
                        > if the explantion doesn't work, I'll draw a graphic ... just let me know.
                        >
                        > I find the
                        > >poundage the same at the same draw length regardless of where I have the
                        > >brace height..The bow is flexed the same amount at the same draw length
                        > >though it is, indeed, flexed more at rest with a higher brace height.
                        > [snip]
                        > >The effect you see is not the result of poundage change but rather
                        > >distance change. For example, a crossbow braced at 4 inches and drawn 10
                        > >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                        > >pull. If the brace height is raised to 4.4 inches it reduces the draw
                        > >length to 9.6 inches. When multiplied against the same 62.5 pound pull
                        > >the result is 600 inch pounds.
                        > [snip]
                        > >If you do actually see the poundage change I would like more information
                        > >on the poundages at each brace height, draw lengths, and construction of
                        > >the bows.
                        >
                        > Ok Carolus, simple physics ... and I'm going to use crossbows as an
                        > example, just because I find it a better mental model.
                        >
                        > Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
                        > string. That gives you some amount of brace height.
                        >
                        > Ok, now imagine the crossbow drawn back and cocked. Assume now, that
                        > there is a 1" wide nut/shelf/etc it is in.
                        >
                        > If you measure the length now, of the string on either side of the nut to
                        > the tip. You will find it is 12.5" ... half the width of the string,
                        after
                        > the 1" of nut is taken into consideration. So the angle the prod is being
                        > held at, is to allow for a 12.5" length of string on either side of it to
                        > exist. Measure the poundage here.
                        >
                        > Ok, now, take the string off and twist it tighter until it is only 25"
                        long.
                        >
                        > Ok, now put it back on the crossbow, and you will have a higher brace
                        > height. Agreed?
                        >
                        > So now, pull back/cock the crossbow. Do the same measurements. Now,
                        there
                        > is only 12" on either side of string. By simple physics, the prod has
                        been
                        > pulled back farther. There is no other way around it. Now, unless this
                        > prod 'somehow' has magical properties that give it a smooth unchanging
                        > poundage (I know of none), the fact that it is being stressed farther,
                        > means it took more force to get it there, and therefore, if you put a
                        > bowscale on it now, the poundage will be higher.
                        >
                        > Now, as stated, the power stroke is now shorter, as the string stops
                        > sooner, and this counteracts 'somewhat' the difference. However, each
                        bow
                        > is different, and some stringheight/poundage is the optimum for that
                        > bow/prod, others are less efficient, therefore, depending upon the bow,
                        you
                        > can adjust it's poundage, and it's power, by playing with that, because in
                        > my experience, it isn't a smooth curve.
                        >
                        > Siegfried
                        > (Who will also sit down and do lots of string pulling on one of his
                        > crossbows for ya if he has to *grin*)
                        >
                        >
                        >
                        >
                        ___________________________________________________________________________
                        > THL Siegfried Sebastian Faust
                        http://crossbows.biz/
                        > Barony of Highland Foorde Baronial Web Minister & Archery
                        Marshal
                        > Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target
                        Archery
                        > http://highland-foorde.atlantia.sca.org/
                        http://archery.atlantia.sca.org/
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                      • Siegfried Sebastian Faust
                        Hey Carolus ... Sorry for the delay in my reply, been sick. ... The point is, that if you take a bow/prod ... and put a shorter string on it, then pull it back
                        Message 11 of 24 , Apr 8 8:22 PM
                          Hey Carolus ... Sorry for the delay in my reply, been sick.

                          Anyway ... I think you are missing something:

                          >No. The pre-stress is higher but the total stress is identical. A spring
                          >tensioned to the same point will only show a certain poundage regardless
                          >of the prestress. The archery mechanics site posted earlier has a good
                          >discussion of spring loading and prestress under plunger buttons.

                          The point is, that if you take a bow/prod ... and put a shorter string on
                          it, then pull it back to the same draw length (not power stroke, but draw
                          length) ...

                          Then because of the shorter string, the 'spring' is NOT tensioned to the
                          same point. To get the shorter string to come back to the same spot, it
                          has to pull the 'spring' farther into deflection. Thereby, stressing the
                          material more, thereby, raising the 'poundage' (While very possibly not
                          raising the power because of the shorter power stroke).

                          Again, clear your mind for a second and imagine a crossbow prod with a 3"
                          brace height, and a 28" string on it. Draw it back to a pin, and you will
                          measure 14" of string on either side of the pin. Now take it off and put
                          a 26" string on it. You have your higher brace height.

                          Now, put it back on the same 'jig', and pull it back to the same pin. The
                          prod is now deflected MORE than it was before, because there is only 13" of
                          string on either side of the pin, forcing the prod to bend more to allow
                          for this.

                          Again, if you need it, I'll draw a picture or take a few photos of this in
                          action.

                          > My results are empirical based on actual tests with a bow scale, not
                          > theoretical.

                          As are mine. I can easily put a shorter string on the same prod and have
                          my bowscale read a higher poundage at the same draw.

                          Siegfried



                          ___________________________________________________________________________
                          THL Siegfried Sebastian Faust http://crossbows.biz/
                          Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                          Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                          http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                        • Siegfried Sebastian Faust
                          ... Exactly ___________________________________________________________________________ THL Siegfried Sebastian Faust
                          Message 12 of 24 , Apr 8 8:23 PM
                            At 06:45 PM 4/2/2004, Scott Jaqua wrote:
                            >Actually Carolus, as a logic thought problem, I come up with more total
                            >stress too. Lower brace height equals a shorter string. A sorter string at
                            >the same draw length means the tip of the limb had to flex further. And thus
                            >more total stress.

                            Exactly


                            ___________________________________________________________________________
                            THL Siegfried Sebastian Faust http://crossbows.biz/
                            Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                            Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                            http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                          • Siegfried Sebastian Faust
                            ... No carolus, it does make a difference, the shorter string causes a higher angle of deflection to get to 28 Siegfried
                            Message 13 of 24 , Apr 8 8:25 PM
                              >This only works if the draw distance remains constant thus resulting in
                              >more draw with the higher brace height. If the bow is drawn to 28", for
                              >example, it doesn't matter if it started with a brace of 7" or 8". The
                              >draw length in the first case is 21" and in the second 20". If, however
                              >we use a draw distance of 20" we get a draw length of 27" with a 7" brace
                              >and 28" with an 8" brace. In this case the draw weight does change.

                              No carolus, it does make a difference, the shorter string causes a higher
                              angle of deflection to get to 28"

                              Siegfried



                              ___________________________________________________________________________
                              THL Siegfried Sebastian Faust http://crossbows.biz/
                              Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                              Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                              http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                            • Carolus Eulenhorst
                              Angles might be slightly different. but poundages have measured the same. There may be some small difference but not enough to read on a scale with 1 pound
                              Message 14 of 24 , Apr 9 12:11 AM
                                Angles might be slightly different. but poundages have measured the same.
                                There may be some small difference but not enough to read on a scale
                                with 1 pound resolution. I would still like to see someone else do some
                                empirical tests on this. Thinking on it while writing this, I might be
                                able to see some difference on a longbow (all my work was on recurves)
                                were the rotation of the tips was not a factor.
                                Carolus

                                On Thu, 08 Apr 2004 23:25:14 -0400 Siegfried Sebastian Faust
                                <crossbow@...> writes:
                                >
                                > >This only works if the draw distance remains constant thus
                                > resulting in
                                > >more draw with the higher brace height. If the bow is drawn to
                                > 28", for
                                > >example, it doesn't matter if it started with a brace of 7" or 8".
                                > The
                                > >draw length in the first case is 21" and in the second 20". If,
                                > however
                                > >we use a draw distance of 20" we get a draw length of 27" with a 7"
                                > brace
                                > >and 28" with an 8" brace. In this case the draw weight does
                                > change.
                                >
                                > No carolus, it does make a difference, the shorter string causes a
                                > higher
                                > angle of deflection to get to 28"
                                >
                                > Siegfried

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                              • Carolus Eulenhorst
                                What numbers have you recorded? Carolus On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust ...
                                Message 15 of 24 , Apr 9 12:12 AM
                                  What numbers have you recorded?
                                  Carolus

                                  On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust
                                  <crossbow@...> writes:
                                  > Hey Carolus ... Sorry for the delay in my reply, been sick.
                                  >
                                  > Anyway ... I think you are missing something:
                                  >
                                  > >No. The pre-stress is higher but the total stress is identical. A
                                  > spring
                                  > >tensioned to the same point will only show a certain poundage
                                  > regardless
                                  > >of the prestress. The archery mechanics site posted earlier has a
                                  > good
                                  > >discussion of spring loading and prestress under plunger buttons.
                                  >
                                  > The point is, that if you take a bow/prod ... and put a shorter
                                  > string on
                                  > it, then pull it back to the same draw length (not power stroke, but
                                  > draw
                                  > length) ...
                                  >
                                  > Then because of the shorter string, the 'spring' is NOT tensioned to
                                  > the
                                  > same point. To get the shorter string to come back to the same
                                  > spot, it
                                  > has to pull the 'spring' farther into deflection. Thereby,
                                  > stressing the
                                  > material more, thereby, raising the 'poundage' (While very possibly
                                  > not
                                  > raising the power because of the shorter power stroke).
                                  >
                                  > Again, clear your mind for a second and imagine a crossbow prod with
                                  > a 3"
                                  > brace height, and a 28" string on it. Draw it back to a pin, and
                                  > you will
                                  > measure 14" of string on either side of the pin. Now take it off
                                  > and put
                                  > a 26" string on it. You have your higher brace height.
                                  >
                                  > Now, put it back on the same 'jig', and pull it back to the same
                                  > pin. The
                                  > prod is now deflected MORE than it was before, because there is only
                                  > 13" of
                                  > string on either side of the pin, forcing the prod to bend more to
                                  > allow
                                  > for this.
                                  >
                                  > Again, if you need it, I'll draw a picture or take a few photos of
                                  > this in
                                  > action.
                                  >
                                  > > My results are empirical based on actual tests with a bow scale,
                                  > not
                                  > > theoretical.
                                  >
                                  > As are mine. I can easily put a shorter string on the same prod and
                                  > have
                                  > my bowscale read a higher poundage at the same draw.
                                  >
                                  > Siegfried

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                                • Carolus Eulenhorst
                                  I just ran this through the calculator with an assumption of 3 being normal brace height and 10 of draw. This changes the angel of deflection by 12 degrees
                                  Message 16 of 24 , Apr 9 12:32 AM
                                    I just ran this through the calculator with an assumption of 3" being
                                    normal brace height and 10" of draw. This changes the angel of
                                    deflection by 12 degrees or about 15.5% while shortening the power stroke
                                    30% and raising the brace 100% to 6 inches (not taking any rotation of
                                    the tips through prod recurve into account. Realizing that the flexion
                                    of a spring in not a linear curve and the fact that I would be highly
                                    suspect of a bow over braced by this amount, yes, in this case you might
                                    see such a change in poundage. However, in practice I don't find it so.
                                    Of course, I have only been working with brace height changes in the +-
                                    1" range, not the 3" in this case. Extremes do make a difference as
                                    shown in some of the "scientific" studies used to prove political points.

                                    Carolus

                                    On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust
                                    <crossbow@...> writes:
                                    > Hey Carolus ... Sorry for the delay in my reply, been sick.
                                    >
                                    > Anyway ... I think you are missing something:
                                    >
                                    > >No. The pre-stress is higher but the total stress is identical. A
                                    > spring
                                    > >tensioned to the same point will only show a certain poundage
                                    > regardless
                                    > >of the prestress. The archery mechanics site posted earlier has a
                                    > good
                                    > >discussion of spring loading and prestress under plunger buttons.
                                    >
                                    > The point is, that if you take a bow/prod ... and put a shorter
                                    > string on
                                    > it, then pull it back to the same draw length (not power stroke, but
                                    > draw
                                    > length) ...
                                    >
                                    > Then because of the shorter string, the 'spring' is NOT tensioned to
                                    > the
                                    > same point. To get the shorter string to come back to the same
                                    > spot, it
                                    > has to pull the 'spring' farther into deflection. Thereby,
                                    > stressing the
                                    > material more, thereby, raising the 'poundage' (While very possibly
                                    > not
                                    > raising the power because of the shorter power stroke).
                                    >
                                    > Again, clear your mind for a second and imagine a crossbow prod with
                                    > a 3"
                                    > brace height, and a 28" string on it. Draw it back to a pin, and
                                    > you will
                                    > measure 14" of string on either side of the pin. Now take it off
                                    > and put
                                    > a 26" string on it. You have your higher brace height.
                                    >
                                    > Now, put it back on the same 'jig', and pull it back to the same
                                    > pin. The
                                    > prod is now deflected MORE than it was before, because there is only
                                    > 13" of
                                    > string on either side of the pin, forcing the prod to bend more to
                                    > allow
                                    > for this.
                                    >
                                    > Again, if you need it, I'll draw a picture or take a few photos of
                                    > this in
                                    > action.
                                    >
                                    > > My results are empirical based on actual tests with a bow scale,
                                    > not
                                    > > theoretical.
                                    >
                                    > As are mine. I can easily put a shorter string on the same prod and
                                    > have
                                    > my bowscale read a higher poundage at the same draw.
                                    >
                                    > Siegfried

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                                  • Bruce R. Gordon
                                    Greetings I approach this discussion with a certain amount of trepidation, since I am definitely not well-versed in the physics of archery or math analysis,
                                    Message 17 of 24 , Apr 9 6:02 AM
                                      Greetings
                                      I approach this discussion with a certain amount of trepidation,
                                      since I am definitely not well-versed in the physics of archery or math
                                      analysis, but...
                                      On a standard bow, say, a #35 recurve, it is often said; 35 pounds
                                      AT 28 INCHES (emphasis mine). I have always taken this to mean that if
                                      I underdraw the bow, I get less than 35 lbs, and if I overdraw it more
                                      than 28 in., I get a higher poundage. Is this the case, and does it
                                      therefore have relevence to the discussion at hand? Or am I missing
                                      some factor here that would make this not to the point?

                                      Nigel FitzMaurice

                                      > I just ran this through the calculator with an assumption of 3" being
                                      > normal brace height and 10" of draw. This changes the angel of
                                      > deflection by 12 degrees or about 15.5% while shortening the power
                                      stroke
                                      > 30% and raising the brace 100% to 6 inches (not taking any rotation of
                                      > the tips through prod recurve into account. Realizing that the
                                      flexion
                                      > of a spring in not a linear curve and the fact that I would be highly
                                      > suspect of a bow over braced by this amount, yes, in this case you
                                      might
                                      > see such a change in poundage. However, in practice I don't find it
                                      so.
                                      > Of course, I have only been working with brace height changes in the
                                      +-
                                      > 1" range, not the 3" in this case. Extremes do make a difference as
                                      > shown in some of the "scientific" studies used to prove political
                                      points.
                                      >
                                      > Carolus
                                      >
                                      > On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust
                                      > <crossbow@...> writes:
                                      > > Hey Carolus ... Sorry for the delay in my reply, been sick.
                                      > >
                                      > > Anyway ... I think you are missing something:
                                      > >
                                      > > >No. The pre-stress is higher but the total stress is identical.
                                      A
                                      > > spring
                                      > > >tensioned to the same point will only show a certain poundage
                                      > > regardless
                                      > > >of the prestress. The archery mechanics site posted earlier has a
                                      > > good
                                      > > >discussion of spring loading and prestress under plunger buttons.
                                      > >
                                      > > The point is, that if you take a bow/prod ... and put a shorter
                                      > > string on
                                      > > it, then pull it back to the same draw length (not power stroke,
                                      but
                                      > > draw
                                      > > length) ...
                                      > >
                                      > > Then because of the shorter string, the 'spring' is NOT tensioned
                                      to
                                      > > the
                                      > > same point. To get the shorter string to come back to the same
                                      > > spot, it
                                      > > has to pull the 'spring' farther into deflection. Thereby,
                                      > > stressing the
                                      > > material more, thereby, raising the 'poundage' (While very
                                      possibly
                                      > > not
                                      > > raising the power because of the shorter power stroke).
                                      > >
                                      > > Again, clear your mind for a second and imagine a crossbow prod
                                      with
                                      > > a 3"
                                      > > brace height, and a 28" string on it. Draw it back to a pin, and
                                      > > you will
                                      > > measure 14" of string on either side of the pin. Now take it off
                                      > > and put
                                      > > a 26" string on it. You have your higher brace height.
                                      > >
                                      > > Now, put it back on the same 'jig', and pull it back to the same
                                      > > pin. The
                                      > > prod is now deflected MORE than it was before, because there is
                                      only
                                      > > 13" of
                                      > > string on either side of the pin, forcing the prod to bend more to
                                      > > allow
                                      > > for this.
                                      > >
                                      > > Again, if you need it, I'll draw a picture or take a few photos of
                                      > > this in
                                      > > action.
                                      > >
                                      > > > My results are empirical based on actual tests with a bow
                                      scale,
                                      > > not
                                      > > > theoretical.
                                      > >
                                      > > As are mine. I can easily put a shorter string on the same prod
                                      and
                                      > > have
                                      > > my bowscale read a higher poundage at the same draw.
                                      > >
                                      > > Siegfried
                                      >
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                                    • Siegfried Sebastian Faust
                                      ... Tonight, and/or this weekend, I will take a few of my crossbows and do the measurements on them and post it here ... Siegfried
                                      Message 18 of 24 , Apr 9 6:28 AM
                                        >What numbers have you recorded?

                                        Tonight, and/or this weekend, I will take a few of my crossbows and do the
                                        measurements on them and post it here ...

                                        Siegfried



                                        ___________________________________________________________________________
                                        THL Siegfried Sebastian Faust http://crossbows.biz/
                                        Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                                        Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                                        http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                                      • Siegfried Sebastian Faust
                                        ... Ok, at least we are riding the same thought train now :) Now that we agree that it can change the poundage ... I agree that all springs are not linear
                                        Message 19 of 24 , Apr 9 6:39 AM
                                          >I just ran this through the calculator with an assumption of 3" being
                                          >normal brace height and 10" of draw. This changes the angel of
                                          >deflection by 12 degrees or about 15.5% while shortening the power stroke
                                          >30% and raising the brace 100% to 6 inches (not taking any rotation of
                                          >the tips through prod recurve into account. Realizing that the flexion
                                          >of a spring in not a linear curve and the fact that I would be highly
                                          >suspect of a bow over braced by this amount, yes, in this case you might
                                          >see such a change in poundage. However, in practice I don't find it so.
                                          >Of course, I have only been working with brace height changes in the +-
                                          >1" range, not the 3" in this case. Extremes do make a difference as
                                          >shown in some of the "scientific" studies used to prove political points.

                                          Ok, at least we are riding the same thought train now :)

                                          Now that we agree that it 'can' change the poundage ... I agree that all
                                          springs are not linear curves (not even close), and that the difference may
                                          in fact, depending on the prod be unmeasureable, or visible.

                                          In my experience, on at least some of my crossbows, it has been
                                          measureable, as I have measured differences.

                                          Again, this weekend I will grab a couple of crossbows and play.

                                          Siegfried


                                          ___________________________________________________________________________
                                          THL Siegfried Sebastian Faust http://crossbows.biz/
                                          Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                                          Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                                          http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                                        • Carolus Eulenhorst
                                          Semantics here. might not can depending on construction and design. I haven t seen it on recurve designs, it is not reported by any manufacturer (their
                                          Message 20 of 24 , Apr 9 7:16 AM
                                            Semantics here. "might" not "can" depending on construction and
                                            design. I haven't seen it on recurve designs, it is not reported by any
                                            manufacturer (their documentation always gives a range of brace heights
                                            with no reference to poundage change) and only appears relevant when
                                            taken outside the safe range of variation of a bow. Many changes can
                                            happen when design specs are exceeded. Please be sure to give all
                                            relevant measurements with your stats. My tests were with a crossbow
                                            using a Iolo prod, braced from 3-5" pulled to a nut 14" from the prod.
                                            Measured a constant 86 pounds.
                                            Carolus


                                            On Fri, 09 Apr 2004 09:39:54 -0400 Siegfried Sebastian Faust
                                            <crossbow@...> writes:
                                            >
                                            > >I just ran this through the calculator with an assumption of 3"
                                            > being
                                            > >normal brace height and 10" of draw. This changes the angel of
                                            > >deflection by 12 degrees or about 15.5% while shortening the power
                                            > stroke
                                            > >30% and raising the brace 100% to 6 inches (not taking any rotation
                                            > of
                                            > >the tips through prod recurve into account. Realizing that the
                                            > flexion
                                            > >of a spring in not a linear curve and the fact that I would be
                                            > highly
                                            > >suspect of a bow over braced by this amount, yes, in this case you
                                            > might
                                            > >see such a change in poundage. However, in practice I don't find
                                            > it so.
                                            > >Of course, I have only been working with brace height changes in
                                            > the +-
                                            > >1" range, not the 3" in this case. Extremes do make a difference
                                            > as
                                            > >shown in some of the "scientific" studies used to prove political
                                            > points.
                                            >
                                            > Ok, at least we are riding the same thought train now :)
                                            >
                                            > Now that we agree that it 'can' change the poundage ... I agree that
                                            > all
                                            > springs are not linear curves (not even close), and that the
                                            > difference may
                                            > in fact, depending on the prod be unmeasureable, or visible.
                                            >
                                            > In my experience, on at least some of my crossbows, it has been
                                            > measureable, as I have measured differences.
                                            >
                                            > Again, this weekend I will grab a couple of crossbows and play.
                                            >
                                            > Siegfried

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                                          • Siegfried Sebastian Faust
                                            ... But of course :) And I will be doing it with a Gladius prod, one of my own custom Power-Tuff Fiberglass ones, and maybe something else. I swear I have
                                            Message 21 of 24 , Apr 9 7:34 AM
                                              >Please be sure to give all
                                              >relevant measurements with your stats. My tests were with a crossbow
                                              >using a Iolo prod, braced from 3-5" pulled to a nut 14" from the prod.
                                              >Measured a constant 86 pounds.
                                              >Carolus

                                              But of course :)

                                              And I will be doing it with a Gladius prod, one of my own custom Power-Tuff
                                              Fiberglass ones, and maybe something else.

                                              I 'swear' I have seen the differences with these :)

                                              Siegfried



                                              ___________________________________________________________________________
                                              THL Siegfried Sebastian Faust http://crossbows.biz/
                                              Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                                              Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                                              http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
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