Are there any supplements that expand upon firearms? Like new rules and creation options? I'm interested in if there are rules for rifle-muskets firing mine balls. In the base game there are only rifles that fire metallic cartridges and smoothbore muzzleloaders.
None that I'm aware of, it a shame they jumped right past 100 years of firearms development. Would have loved to see cap & ball revolvers , needlefire paper cartrages and trapdoor rifles instead of jumping straight to the modern smokeless metallic cartrage.
It wouldn't be difficult to craft intermediate firearms (I added a "Carbine" to Early Firearms for my Iron Gods game pretty easily), but I am afraid that anything much beyond the given Early Firearms will out-do what the game is expecting (running Iron Gods, it's become clear to me that a Revolver is pretty much superior to the Technology Guide's Sci-Fi Firearms) so you should be prepared for that.