Timerover,
There are some smokeless powder replacements for black powder. Notably found in the muzzleloading community with those darned pellet powder guns.
Yes, there would be issues with TL incompatabilities, but if the product meets all the specifications, well, can't hurt to try, can it?
As to the Martini, well, it seems more TL3+, wouldn't quite put it at TL4-, so well, I used a bad example for a TL13 gun, but I do know someone who shoots one, and a Springfield Trapdoor. Cartridges are out there, and some reloading equipment. Using modern black powder (which some varieties burn cleaner with lots less waste (smoke) and fouling than traditional black powder) he even goes hunting with his Martini. For reenactment events, he likes regular smoky black powder, by the way.
Crazy things chemistry can do.
That's why I did the TL4-TL15 spread. If we extrapolate the future from today, there will be some dudes out from a TL15 there who are doing reenacting of the Vilani version of the Anglo-Zulu wars, or maybe the Crimean campaign, and using Vilani versions of the Martini built in their modern times that meet the specifications of the ancient Vilani Martini.
Undoubtedly there are some TL14 Solomani out there doing the Crimean reenactment thing. Maybe with an original Martini or two. I've seen stranger things (English Civil War reenactors using actual English Civil War artifacts during their fun games (and that's a 400-500 year gap between ECW and the reenactors.))
But, yeah, maybe I went too low in my TL example. Maybe TL5?
Actually they aren't actually smokeless. They are just substitutes for The Holy Black, There are Pyrodex, Triple 7, Trailboss (which is formulated for BP Cartridge guns). Generally only Pyrodex is found in pellet form. I shoot BP guns a lot which is how I know.