The Harper's Ferry type guns can run hot & cold because of the lock style. Presently, these guns seem to be better tuned and heat-treated. The initial problem is that they are a "basher" style lock which has the problem of geometry of the hammer and frizzen. The flints can be shattered because of the method at which they contact the frizzen which is more straight-on then in a sweep like many other lock types. Early on these were improperly heat-treated and the hardened surface was extremely shallow. Even light stone work could eat through the hardened surface and prevent the spark from happening. This may have been sufficiently addressed since I haven't heard the problem mentioned recently.
The basic was a poorly designed lock that suffered even worse due to the shrinking of the parts when cast in molds taken from original lock parts. Some time ago, the only solution wass to convert the locks using parts from modern locks. I really don't think is as serious as earlier. You will probably find the flint needs to be set with the edge down to get it down about 1/3 the distance from the top of the frizzen to the bottom. Actually, the problems can be corrected with minimum fiddling, if they exist at all with the current production. Don't mean to scare you off the pistol, just wanted to let you know the possible problems and solutions. Good luck.
