Lancaster (Howdah) Pistol - A four barrel handgun in .455 or .577 (basically a Martini Henry rifle round). - These custom handguns were used for defence against big game such as lions and tigers in the African bush, and were used as officer sidearms up to and during WW1. Their break...
I'll set the 1880's as the maximum decade and we'll search what fits into it, for sure we wouldn't see those weapons from RDR2 again: Double-Action Revolver, Semi-Automatic Pistol, Mauser Pistol, M1899 Pistol, Varmint