Effects of a different propellant on early firearm design?
Cat: So, we're making a setting for a slightly home-brewed Pathfinder 1e campaign. We want guns in the campaign, but the official firearms rules are irksome.
Cat: Anyway, as one of the changes we've made, we've switched propellants to a technically magical explosive called Force Powder. Force powder is smokeless, does not foul the workings of a gun, operates just fine in water, and can only be set off with a sharp percussive force; examples include smashing it against a metal surface with a hammer, or an explosive shockwave.
Cat; Among other things, we've figured that this will probably make rifled firearms a fair bit more popular early on than in real life; one of the big reasons they weren't widely adopted for military use is because all the smoke quickly nullified their range and accuracy advantages. It also means that matchlocks, wheel locks, and flint locks basically don't exist, with only percussive ignition being feasible.
Cat: So, are there any other things we should be aware of?
Lucifer: We're uncertain of the effects on breech-loading firearm adoption. It seems like it should help?
Percussive force setting off the powder is going to open up roleplay possiblity. A few thoughts on this:
Does smacking someone's gun with a stick cause all the rounds to go off?
What happens if you fumble the rounds and they hit a rock on the ground?
How is ammo transported?
For other ideas of the problems this would cause look up dynamite from ye olden times. It was known to be unstable if it was "sweating". Leading to accidental explosion from being handled