The 45 Colt . . . now there's one that may not be THE most historically significant cartridge, but it's one that has a truly fascinating history in and of itself. And, as Sandwarrior correctly points out, a great deal of its historic reputation more properly belongs to the 45 S&W cartridge, or one of the derivatives such as the nearly identical 45 Schofield or the 45 Colt Government (AKA 45 Short Colt). Add to that the M1909 version of the 45 Colt, and yeah, there's a wild history there.