I set my rifle in my gun rest. Notice just the very edge of the nail is on the edge of the flint. You're not trying to bust off a large flake. If you take to much you will damage the flake.



This is a flint I just napped. Notice just very small flakes off the nose of the flint are removed. But if you rub your finger over that, you'd probably end up with a cut.

I tried it NCHawkeye's way with the thing under my arm, but I kept hitting too far back and breaking the flints. So I just set mine in the gun vice/shooting rest and then again.. very small flakes remove.