Tips:
- Use real black english flints by Tom Fuller
- Make sure the flint is in the right spot (60%, bevel up/down) and secured in the cock jaws
- Secure the flint with lead sheet
- Make sure your lock is well tuned
- Store your flints under water
- Use real BP in your flinter (never use pyrodex!) 3F is the best all around general powder
Arkansas flints are too hard and tear up frizzens. Then you will have to re-surface and possibly re-harden after a short time of use. Don't use Arkansas flints, as they are more expensive than a hand-flaked flint.
I get between 80-100 shots out of EACH 5/8" x 5/8" Tom Fuller black english flint in my pistol. It has a small Siler lock that I tuned. Sparks like a dream.
I get between 40-50 shots out of EACH flint by using my Traditions Kentucky flinter because it's lock isn't so well-tuned. Occasionally it will shatter one, but I carry extras and can re-knap using the frizzen unless the break is extreme.
Your flint should be held in lead (here we go) sheet pounded flat to ~1/8" from a .50 cal ball and cut with scissors. Typically, I tighten my flints down, make 5 snaps, then re-tighten. I re-tighten every so often just to make sure it's not loose. SInce I switched to lead, I've had fewer problems.
Check to make sure your flint isn't striking anywhere other than the frizzen surface. If it strikes the side of the pan or barrel, it can shatter. Make sure your frizzen spring is not too strong, the lock should spark well with no frizzen spring at all. The spring simply keeps the frizzen in place and pan covered.
Try storing your flints under water. Takes at least 3-6 months to see a benefit. I have just started trying this and supposedly it helps. No BS.
Make sure your flint is the right size. At half cock, the flint should be ~1/16" away from the frizzen. If it's too far away, you either need to move the flint forward or but a larger flint. My locks like flints bevel down, I get a better hit on the frizzen surface. You want the flint to hit around 60% up the face of it to get the most sparks. If bevel up gives you this location, use it. But, flip the flint upside down and try it this way as well. You can't tell immediately, you will have to try many shots.
The quantitiy of spark produced by a well tuned flinter is amazing to see in slow motion. You can only see a small portion of what is produced with your naked eye. Using a darkened room and an open shutter on my camera, I counted over 100 white hot sizzlers that were bounced out of the pan and into the air. Not to mention all the ones that hit the pan!