Here is a full weight, purportedly all copper 1965 quarter:
I have come across a number of full weight, all copper quarters. All
were suspicious, for any of several reasons. Some had obliterated
reeding; some had a suspiciously porous surface; one had a piece of
copper foil overlaying the design. If this is truly a pure copper
quarter, then it may be a struck counterfeit.
Full weight, pure copper dimes and quarters are possible, however. I
have one full weight, pure copper dime that appears genuine. In the
bonding mill, if both clad layer strips run out before the copper
strip, then the latter will be rolled to full coin thickness. Any
coin punched out of it will be a full thickness, pure copper quarter.