Well, both sides are flat, and I just lightly tap the front of the flint at a 45 degree angle. You will see very small flakes coming off, and just try to keep the flint straight. Never toss flints, you can use larger leather in the jaws, or even lead wraps to push the flint forward in the jaws
Here is my hammer
View attachment 42841
L&R lock, they told me about a match shooter that had over 3600 shots on the frizzen of one of their locks. They did tell me the frizzen was nearly broken through, but still doing the job. The guy came by to buy a spare frizzen, in the event of failure