I'm not sure if there ever was a cartridge marked ".45 Short Colt", but the general terminology resulted from the 1870's when the US Cavalry was being issued both Colt Single Action Army and S&W Schofield revolvers. The Colt could chamber and shoot both the .45 Colt cartridge and the shorter .45 S&W (Schofield) cartridge, but the Schofield revolvers could only chamber the shorter round. About this same time, the Army also reduced the powder charge in the .45 Colt cartridge so they were easier to shoot from horseback. Because of the ammunition issue, the Army standardized on the .45 S&W cartridge in both guns to prevent problems that had originally occurred with Schofield-equipped units being issued .45 Colt cartridges. Over time I believe the two cartridges were given the name "Long Colt" and "Short Colt" simply as an easy way for the user to indicate which cartridge they needed. The Army eventually solved the problem when it sold off its Schofield revolvers, but it had a large amount of the shorter Schofield ammunition still on hand and continued to issue it to cavalry units for use.