There is an interesting class of old muzzle loader that may have been overlooked in this discussion. In wealthier economies, shooters moved from flintlock to percussion to cartridge as soon as they became available but in poorer societies, the market for muzzle loading weapons continued into the 20th century.
have pistols from the 18th and 19th centuries but my flintlock long gun was made in Birmingham for the "African Trade" in the early part of the 20th century! My percussion double shotgun was also a 20th century weapon and was in use in Russia as recently as 1942. Antique or not, I find them amusing niche items. I wonder if other forum members have encountered such oddities?