The 41 Shot Colt, Single Action was launched in 1875 together with the series of Colt New Line single action revolvers. The rim diameter of this round was larger than the double action versions and the chamber distance in the single action revolvers were greater so that if these were used in the double action revolver, only every other chamber could be loaded. According to White & Munhall only UMS and the US Cartridge Company loaded the single action cartridge. Discontinued probably by the early 1880’s with the introduction of the double action cartridge. (Erlmeier, Brandt Ref. 392)