Actually, percussion caps is as far back as we’d have to go.
Flintlocks require black powder, and black powder ground very fine. Very fine black powder is, IMO, more dangerous than priming compounds.
Yes, but it doesn’t have to be packed precisely like a primer and you don’t have to worry about each little anvil being in the right place. Chlorate primers are corrosive too. The tolerances for cartridges to operates consistently are a lot tighter, plus it would be very time consuming to produce enough by hand. If it were to come to not having any primers available, I imagine by then there wouldn’t be any smokeless propellant either. We’d end up going back to manufacturing our own black powder like mentioned earlier.