Good post SCLoyalist - so much we take for granted thinking everyone knows - but sometimes don''t. shooting a flinter is a learning experience, for sure and something we must go through. People cannot be told everything there is to know about any shooting subject - they must actually do it, then ask questions if there are problems that can't be figured out. the internet is a great source of information, at times, too great. It cretes a new phenominum, one that stymies some people into a semi-frozen state, thinking they must have all the information before doing anything. I know there are builders who feel this way as well - some people have come to rely on the net and won't do anything for themselves any more. This is not aimed at anyone and is merely an observation of human interaction and trends we've made over the years - it will persist and we will continue trying to help in any way we can.
I've found a new flint can be knapped back a long ways before ignition suffers in any form- be that slower ignition or failure to open the frizzen. Bevel up or down also changes the location the sparks hit the pan. Some locks prefer one or the other - much depends on the angle of the cock's jaws and the arc of travel. Much also depends on the flint - some cannot be placed bevel down due to angles of the top surface and the way the jaws hold it- causing it to strike over the frizzen or too close to the top. Lukily, I've a couple locks that allow either bevel up or down - when a flint gets dull shooting bevel down, I can reverse it, snap it once and it 'freshens' itself and continues to spark perfectly - until it gets dull- reversing continues the process - did it few times just to see what would happen - worked fine - mostly can't be bothered with that much finicking around, but it does work - on locks that allow it. I mostly leave the flint alone, knapping as necessary until it's too shot, then toss it and screw in another.
Virtually all of our "shooting" of muzzleloaders is on the trail walks - little is done when hunting. You learn your rifle or smoothbore at a range, gravel pit or while potting bunnies - not while hunting big game. Get out and do a p--s pot full of shooting, as often as possible - Once a week is good. Learn your guns and develope techniques that work for you.
Round Ball made the same observation about flint reversal some time ago and noted it here on ALR.