I find lead holds the flint *a lot* tighter than leather. For me this has meant more sparks and easier knapping - the leather being softer than lead acted almost like a shock absorber.

If you use leather to hold your flint try lead and see if that does not help things. It is very easy to do. What I do is place a round ball on concrete and flatten it with an engineers hammer (use a regular hammer if that is all you have). Experiment to determine how thin you need to pound the ball. You want it thin enough so you can wrap it around the flint but not so thin that the lead breaks or there is not enough to hold the flint. Use snips cut out a rectangular piece of lead the same width as the flint and long enough to wrap around the flint - the same size and shape as you would use for leather. Tighten. Here is where things get interesting. Lead being a soft metal it will need a bit of time to take to the shape of your flint and the ridges along the inside of the c0ck jaws - "jimps" I believe they are called. Position the flint where you want it and do a first tightening with the lead. Wait about an hour and re-tighten. The flint should be held very tightly at this point. Try some (unloaded!) test fires with no powder in the pan, you should be getting more sparks. You should also find it much easier to knap using the method Cayugad and others described.

Best of luck!