Originally Posted by
Omnivore
Maybe we should discuss the "machinery" of percussion ignition.;
Ever heard of a "fire piston"? If not, please look it up and read about how it works, then come back to the conversation. In short, it's like a Diesel engine-- compression alone leads to the high temperature that initiates combustion.
A percussion cap works very much the same way. The cylinder is packed tight with powder, and the end is plugged with lead. It's a blind hole, so "fire" isn't just going to "blow" into the chamber like wind. The caps's "fire" may help, by mainly it is the intense spike of high pressure that lights up the atmosphere, inside the flash hole, and between the tiny air spaces between granules right at the back of the chamber. We tend to think of it as a "spark" lighting the powder, like the spark in a cigarette lighter as at actually touches the thin zone of vapor/air mix at the wick, lighting it directly. But it's not really quite like that. It's more like Diesel ignition.
Leaving a nipple open, beside a fired one, may let in a teeny bit of heat and light through the pin hole, but it doesn't provide for that intense compression.
A flintlock by contrast relies mostly on the direct radiant heat from the flash in the pan. There's a little bit of compression there, but not near enough. The idea of a "whoosh" of flame entering the flash hole doesn't make a lot of sense, because it's a blind hole. There's no accommodating volume of air inside to make room for such incursion. Getting the main charge closer to the flash, by counter-boring the flash channel, is a we-ll known way to improve ignition time. Still, it is common enough to get a flash in the pan and still not ignite the main charge.
You could try lighting a small charge of black powder using a fire piston. If you do, and once your wrist is healed up from the amputation of your blow-up hand, then report back here and tell us that "sparks" are not needed to set off black powder, that compression of a small air space does a great job of it.