Have not had much luck with saw-cut flints: they are expensive, seem to get dull quickly and I have not been able to knap them back to sharpness.
The only success I've had or read about with sharpening the cut flints is to grind them back to shape with a diamond lap or some similar coarse abrasive. These can also work for touching up and/or reshaping regular knapped flints, but most prefer knapping one way or another. For regular flints, I usually pressure-flake them with antler or copper, but that takes a bit of practice.
In addition to the tools & techniques already mentioned, a handy knapping tool many use has a ledge or notch 1/32-1/16" deep, that one sets on the edge of the flint and taps with a hammer, knife handle, short starter, etc. to take off small chips. This may be as narrow as the corner of a turn-screw blade or wide enough to trim the whole edge at once, but most are in-between, cut near the end of some round or square rod or some other tool. The shallow depth of the notch keeps you from accidentally breaking off too much of the flint. A somewhat similar item I've seen that I seem to recall being possibly found in period looks like a miniature blunted hatchet that you set across the edge of the flint and tap as above - this requires a bit more care in use. NOTE that whenever you are knapping the flint while it is still in the ####, it is best to do this at half-####, then hook a finger underneath the lower jaw to pull the #### back slightly and support the bottom of the flint. This is to avoid unnecessary stresses on the tumbler and sear.
Another technique that some use (and I've used occasionally) is use the lock to knap the flint against the heel of the hammer/frizzen. Pull the #### back just far enough that you can close the frizzen to where the flint sits on it just above the bottom. Then hold the frizzen in exactly that position while you bring the #### back to full-#### and pull the trigger - this knocks a row of small chips off across the whole edge of the flint at once.
These techniques raise important safety matters that are sort of obvious and may already have been raised, but I can't remember, so I'll belabor them anyway. These are consequent to the fact that a single stray spark that bounces into the touch-hole could fire the gun. Some firelocks will go off when tried without priming a surprisingly large fraction of the time, and any will go off at least occasionally. Therefor, ideally, any knapping and/or adjusting of the flint while in the lock should be done with your firelock EMPTY. There are times when this is very inconvenient, so then you should dump the prime, brush/wipe all the priming granules from in and around the pan (that's what those flintlock brushes are for - not cleaning),
plug the touch-hole,
and keep both the muzzle and the touch-hole pointed in safe directions throughout the process. Even if your tools are non-sparking (antler, copper, brass, soft iron),
BE PARANOID! "Murphy" can be nasty, and you never know when he's paying a visit. "That shouldn't have happened!" is something you do not want associated with potentially lethal items. Should I mention that I still have some bits of the spotty black tattoo you can get from the touch-hole even without priming? A little inattention when dealing with a misfire was enough!
Regards,
Joel
