After the Civil War there were two pistol companys competing. Colt and S&W. Surprise! Colt made the "Peacemaker" as we still know it using the .45 Colt round, quite long. S&W had a single action with the "break" mass ejection feature. A modified design for the cavalry became the Schofield, so named for Mjr Schofield a cavalry officer and designer. It took a .45 cartridge that was shorter, BUT would fire in the .45 Colt cylinder... Less powder and less power... somewhat.
Of course the Army QM (Quarter Master) consistenly provided the longer Colt round to troops armed with the S&W revolvers... totally useless AND troops with the Colt got the less powerful .45 S&W round which was workable but less powerfullllllll....
ERGO the orders came in for ".45 LONG Colt" ammunition...(not .45 S&W which is shorter) except where the gun was S&W and required NOT the Long Colt round...
Slang lives. And the term "long Colt" survives. Then there were less powerful and less costly rounds made for guns for practice, not unline the rimfire "short," "long," and "long rifle." There was an "extra long rifle" too. The Sears catalogue reprints from 1908 are quite instructive. Yes, if you go by only the factory lists and not real life experience it is seldom "long Colt." Otherwise, you, today, have ".45 Colt" /.45 Long Colt or .45 ACP (Automatic Colt Pistol) except that the Schofield is back in production as a copy, Navy Arms I think, and so you can still find the .45 S&W... which can be used as a short, less powerful Colt round... Stop when your head starts to hurt... Enjoy the gun. luck.