Knapping the flint is important to restore the sharp edge required to get good sparks out of your frizzen. But you don't have to knapp the whole edge!! Often, there is a small round nub that acts like a roller bearing forcing the frizzen to open before the rest of the flint gets a bite of the steel. Many times, you only have to find and remove that little nub.
I use a "T" handled tool with a copper "T" and a screw driver blade for the handle. The copper is heavy and soft enough to deliver the force required to remove a flake in a precise manner. In operation, I place the lock in half cock, place my right index finger under the flint and use the forward weight of the rifle to lift the cock off the half cock notch but not all the way to full cock. Now I strike down and back on the edge of the flint with a sharp whack, often starting on a corner. This will remove a long flake from the bottom of the flint running back all the way to the bottom jaw. The next flake is struck right next to the first. The scar from the first flake will make the next flake come off parallel to it. In this way, go all the way across the flint if that is necessary. CAUTION. Do not try to wipe this new edge with your finger no matter how tempted you might be. It will cut you very deeply. But again, study the flint's edge carefully first to see if only a small nub needs removing. This will extend your flint's life.
There are a couple of things other than a dull flint that will cause a misfire. Your flint must be tightened securely in the jaws of the cock to get good sparks every time. If the flint can move sideways, it will, and the result will be a hammer fall without ignition. In some contests/trails, the shooter gets only one hammer fall per station, so attention to one's flint is crucial. To help avoid this catastrophe, it is helpful to change the flint leather every time you change the flint. When you install a new flint and leather, the leather is crushed between the steel of the jaws and the glass hard stone. Every flint has a slightly different shape, and the leather forms to it holding it securely. Once used, it is unlikely that the leather will hold the next flint as tightly, unless it is changed. I find the leather from welding gloves' cuffs to be excellent for this job, and dozens can be cut from each cuff. Your patchbox is an appropriate place to store and carry flints and leathers.
