If you value your flints, don't buy a knapping hammer. If you insist, send me a PT with your mailing address, and I will send you my old knapping hammer. I haven't used it in years.
INSTEAD: With the gun empty, put the hammer on the half cock notch, and then use your Left thumb's outside edge to lift the frizzen up until when you lower the cock so that the flint's edge will touch the frizzen, its touching at the bottom of the raised frizzen. Now, hold the frizzen at that location, making sure your thumb is back away from the face( avoid cutting). Cock the hammer to full cock, and pull the trigger. The flint will strike this lower end of the frizzen at the " heel ", and the very severed angle of impact will remove a thin part of the edge across the entire width of the flint. The blow will knock off a sharp angle from the bottom edge of the flint.
This is all the Knapping You will ever need to do, either in mounting the flint to squared the edge in the first instance, or to re-square the edge when you have to move the flint forward as its used.
The flint should not touch the frizzen when the cock is in the half cock notch. I prefer to see 1/32" of daylight between the frizzen and the front edge. Now, lift the frizzen up and open, so that you can manually lower the cock all the way forward. The flint should be set in the jaws so that the inside edge does not scrape or strike the barrel as the cock falls, and the flint should not extend so far forward of the jaws that it strikes any portion of the frizzen pan. That is how you determine the correct POSITION of the flint in the jaws for best functioning.
In a good lock, the flint should point to the middle or slightly forward of the center of the pan. If it points so far forward that the edge is looking past the front of the pan, you are going to have trouble getting the sparks into the pan for quick ignition. If the flints points behind the pan, you will also have that problem.
With each shot, the flint will break off a bit of the edge, giving you a new edge for the next shot. Remember, you are cutting steel, so a new edge is a good thing! But, this also wears down the flint, and the sparks being thrown will move from the front side of the pan, to the center, and then to the rear of the pan.
Check this, with an empty gun and empty pan, by holding the gun out at arm's length, so you can look at the pan when the cock falls, and fire the lock. Watch where your sparks are actually landing. Final adjustment of any flint is based on where those sparks are landing. Sparks that miss the pan aren't doing you any good at all.
When YOu move a flint forward, from wearing back, use a twig or small piece of wood to hold the flint and flint wrap forward. A good flint will give you more than 80 strikes in a well tuned lock. Tuning means the springs are not so heavy that they are crushing your flints when they strike the frizzen. Tuning means the angle of impact of the flint is 60 degrees, and that the edge of the flint strikes the flint between 60 and 66% percent of the distance UP from the bottom of the frizzen face. That insures that the frizzen will be knocked back and open to give clearance for the sparks to be thrown into your pan.
Widening and lengthening the pan will give a bigger target for your sparks, and allow you to get more shots out of a flint that is wearing down before you have to move it forward, or, finally, replace it.
Tuning the lock also means addressing the contact point between the frizzen cam and the upper arm of the frizzen spring, so that there is NO tension from that spring resisting the frizzen from opening when struck by the flint. The only tension needed from the frizzen spring ( Or feather spring) is to keep the frizzen close when the muzzle is pointed down. This keeps any priming powder from falling out of the pan if you have to point the muzzle down for some reason. The tension of the feather spring is NOT for the purpose of helping the flint edge DIG into the frizzen face. The flint scrapes steel from the frizzen. If you flint is gouging the frizzen, the lock needs to be tuned.
See my article on shooting and tuning flintlocks under " articles " in the Member Resources section at the top of the index page to this forum. If you have questions about tuning your own lock, send me a PT. I have some techniques that are not described in that 2004 article that I have learned since I wrote it.
