I often take 1 1/8" musket flints (of which I have about 200) and shorten them to go in my PA Fowler and Virginia rifle, ie: 7/8".
I put a piece of folded heavy (1/4") leather in my machinist's vise, place the flint in the leaver with just the butt end sticking out, and with a piece of copper rod and a hammer, knap off the end to shorten the flint.