@GoodRabbitPilgrim, in a well tuned flintlock, there is no acceptable misfire rate. If there is a failure to fire, delay to fire or flash in the pan, then there is something out of tune in the lock. This may be a dull flint, a blockage of the touch hole, fouling internally or wearing of the frizzen. These may not be far out of tune. but they do require maintenance of the lock and the internals to keep everything functioning. It means that while shooting, one must continue to monitor the edge of the flint, keep the touch hole clear and wipe fouling from the pan to maintain reliable firing.
That being said, misfires do happen, but should not happen on the first shots while hunting. The same sort of misfires can happen with percussion lock firearms also.