Stormrider; i would offer that the first books you read are those from DC Waldorf. There are several and The Art of Flint Knapping may be the one you want. As far as material is concerned, good quality flint about your only option. Hornstone and some of the better cherts will make a functional gun flint. Generally, the whiter the stone is, the harder it is, leaning toward a quartz type structure. As opposed to flint where the blacker it is, the harder. Obsidian and the glasses, while sharp as all heck, cannot be used for guns as they very brittle and would be destroyed at the first drop of the hammer. Conversely, they make the sharpest, best broadheads. As you've already found out, finding good quality material is always a problem, unless ya live near Flint Ridge, Ohio or some other known flint deposit. Chert can be found almost anywhere east of the Rockies, but the quality very's widely. You can check any piece you find on a fire steel before investing the labor to make a gun flint. I'm sure our forefathers used anything available and weren't the least concerned about longevity, as long as it fired. Throw it away, make another! Hope this helps a bit, Good luck, Buzzard