Originally Posted By: Gregdownunder
...Older caplocks sometimes have "vents" on the side, I gather the theory of these being excess pressure relief...

I've read before that those vents were not to vent excess pressure, rather a theory at the time that the then new percussion system suffered a disadvantage in that the powder couldn't "breathe" to achieve best combustion, like the old vented flint system.

Whether a like for like muzzle v breech/cartridge load would develop more or less pressure is an interesting question, regardless.