I once missed an opportunity to kill a trophy black tail buck, because my flint was a little loose, and didn't spark. I vowed to never let that happen again if I could help it. After much experimentation I found a cure. I use a medium weight leather wrap (never lead), I notch it to span the jaw screw, and with a knapping pin, made from a short piece of quarter inch steel rod, with a very small step on one end, I notch the heel of the flint. Soak the leather, put it in the jaws,and tighten it up, and forget it. If you use the knapping pin to sharpen your flint, instead of a hammer, the flint can last for a hundred shots, if the lock is of a size to take a large flint. I have gotten sixty shots out of a small pistol lock using this method.
Hungry Horse