There is a method of getting a quick edge. Tip the frizzen forward, lower the cock with your thumb and tip the frizen slowly back until the bottom edge rests on only the very tip of the flint, then squeeze the frizzen down hard. It will flake the edges that stick out the furthest, and give the finished edge a perfect alignment with the frizzen. The trick is to get just 1/32" or less of flint under the edge of the frizzen. I've seen guys smack the frizzen hard when doing this, but I think that is counterproductive and MUCH harder on the lock.
I use this system often. Obviously THE GUN MUST BE UNLOADED and it is probably bad for the frizzen pivot point (but that's built to absorb a sharp blow from the cock. Works soooo nice and it is the fastest way to get off a shot if your flint fractures without igniting the pan (but then, the gun would still be loaded - so do as I say, not as I do /ubbthreads/images/graemlins/wink.gif)