arcticap, it,s leather. i tried a piece of thin sheet lead years ago and it worked, but when you tightened it and used it for a while you had to retighten the jaws, with leather when you tighten the jaws the leather does not take a set like lead and stays snug longer. plus it is easier to work with(put in and adjust as the flint wears down). i started shooting black powder in 1963 and there was not to much to choose from then, today we have guns fron 89.00 to the sky,s the limit. i have 18 black guns right now, i just sold a thompson center pa. hunter 50 cal. flint carbine to a friend(i never got used to the short barrel.) with what av50gary said, if you have a thin neck on your hammer i could see that happening. eastbank.