There are several ways to knap a flint...You can do it with a small brass hammer....just put your finger under the leading edge and lightly tap...this will roughen up the leading edge...You can also hook the flint under the frizzen and remove small flakes from the leading edge...You can flip the flint over and continue to shoot and it will be knapped each time you drop the cock...

The best way I have found is to keep a small finishing nail (with point filed flat) in your patch box...with the small brass hammer, hold this nail at a 90 degree angle to the flint and tap straight down...moving the nail along the edge as you go...this takes off a small amount and helps the flint last longer.

I use this last method the most...always during informal shooting...When I am deer hunting I always start with a fresh, new flint....I check one time and don't use again until I have a shot.