Gun flints are made by striking off one end of a flint nodule, then striking off flakes vertically from the flattened end, resulting in fluted sides. Those flakes are discarded. The gunflint flakes are then struck off from between the first flakes (the raised 'flutes), and will be flat topped, with two sharp sides. The gun flints are then struck off of those long flakes in the widths needed. One of the issues of 'The Missouri Archeologist' (sorry, I can't remember the issue) Has an extensive article describing how to do it, and the tools needed. I am pretty sure it can be accessed on line.