The .45 Colt cartridge was a joint development between Colt's Patent Firearms Manufacturing Company, of Hartford, Connecticut, and the Union Metallic Cartridge Company of Bridgeport, Conn. Colt began work on the revolver in 1871, and submitted a sample to the U.S. Army in late 1872. The revolver was accepted for purchase in 1873. The cartridge was of outside lubricated type, but eliminated the rebated heel type bullet, often attributed to a Russian designer. The Colt replaced the .50 caliber Model 1871 Remington single shot pistol and the various cap-and-ball revolvers converted to take metallic cartridges then in use. While the Colt remained popular, the Smith & Wesson M1875 Army revolver, the Schofield Model, was approved as an alternate. The S&W revolver took a shorter cartridge, which would also work in the Colt, so Frankford Arsenal, then almost exclusive supplier of small arms ammunition to the U.S. Army, dropped production of the Colt round. The M1875 round was replaced by the .38 Colt in 1892. In 1909, the .45 M1909 round was issued along with the Colt New Service revolver. This round was never loaded commercially, and is almost identical to the original Colt round, except having a larger diameter rim. The rim is large enough that it cannot be loaded in adjacent chambers in the rod-ejector Colt model.
The cartridge, and revolver, also were very popular commercially. Today it remains very popular with renewed interest in western type shooting, as well as a round used for hunting.
The 45 Colt originally was a blackpowder cartridge, but modern loadings use smokeless powder. The original blackpowder loads called for 28 to 40 grains (2.6 g) of blackpowder behind a 255-grain (16.5 g) lead bullet. These loads developed muzzle velocities of up to 1000 feet per second (305 m/s), for a muzzle energy of 566 ft·lbf (766 J.). Because of this power and its excellent accuracy the .45 Colt was the most-used cartridge of its time, succeeding the .44 WCF (also known as the .44-40 Winchester) The 45 Colt never enjoyed the 44-40's advantage of a Winchester chambered for it, allowing use of the same cartridge in both pistol and rifle; modern Winchesters , Marlins and replicas have remedied this omission, and the 45 Colt is a very potent round fired from the 16"-20" barrels of modern lever-action rifles. It was said that the cartridge was powerful enough to knock a man to the ground in a single shot. It was also extremely accurate for a pistol of the time, and remains so today if carefully loaded. With careful handloading the original loads can be safely replicated using modern powders.
Today's standard factory loads develop around 400 ft·lbf (542 J) of muzzle energy at about 860 feet per second (262 m/s), making it somewhat more powerful than the .45 ACP. There are also Cowboy Action Shooting loads which develop muzzle velocities of around 750 feet per second (230 m/s).
Some very heavy handloads and some cartridges loaded by small companies exist that put this round in the same class as the faster .44 Magnum. Such loads are not issued by major companies such as Winchester and Remington.
These loads cannot be used safely in any original Colt Single-Action Army or any replica thereof (such as those produced by Uberti or Beretta, and guns like the Taurus Gaucho, or Ruger New Vaquero.) They should be used only in modern large-frame revolvers such as the Ruger Blackhawk, any gun firing the .454 Casull cartridge, or single-shot hunting pistols and modern rifles with strong actions (such as the Winchester Model 1894, Marlin Model 1894, and new clones of the Winchester Model 1892) chambered for the cartridge.
135 years after its introduction, the .45 Colt still enjoys a wide range of uses. The .45 Colt makes a good hunting load, within its range limitations. Standard loads are good for animals the size of deer and black bear, and the heavier hunting loads will take about the same range of big game animals as the .44 Magnum, but less effectively, as the bullets of the factory loads move comparatively slowly and have a steep trajectory making long-range hits more difficult. A two-barrel derringer is also still sold that is chambered in .45 Colt, and these derringers will also chamber a .410 bore shotgun shell without any modifications being required. Similarly, .45 Colt cartridges are still fired occasionally, though not good for the shotguns, in .410-bore shotguns by U.S. farmers needing to kill a mule or horse humanely. However, the most popular use for the .45 Colt today is in Cowboy Action Shooting, where the round is fired from either originals or replicas of the 1873 Colt Single-Action Army or similar guns of the period. Winchester, Marlin and others produce lever-action rifles for the venerable round, Colt has again resumed production of the Single-Action Army, and many SAA replicas and near-replicas as well as modern-design single-actions by Ruger and others ensure that the .45 Colt will live for many more decades.
The cartridge was a joint development of Colt Patent Firearms Copmpany and the Union Metallic Cartridge Company. Colt began work on their 1873 Single Action Army Model in 1871. Sample cartridges submitted for Army tests were made by UMC, using the Benet cup primers; commercial ammunition used the Berdan-type primer, followed by the more common Boxer priming. Original UMC loads used a 40-grain powder charge and 250-gr. bullet. This was reduced to 35 grs. of powder, and later, by the Army, to 28 grs
The .45 Colt is the basis for the much more powerful .454 Casull cartridge, with the .454 Casull having a slightly longer and stronger case. Any .454 Casull revolver will also chamber and fire .45 Colt, but the inverse is impossible due to the Casull's longer case.
The .45 Colt, when loaded to its potential, produces greater power with less recoil and chamber pressure than a .44 Magnum. All of this is achieved with a larger caliber bullet.
The .460 S&W Magnum is an even longer version of the .454 Casull and the .45 Colt. Likewise, .460 Magnum revolvers can also chamber and fire the two lesser calibers, but again, the inverse is impossible.
The .45 ACP round produces inferior game killing ability, as it cannot use heavyweight bullets. It uses a much shorter overall cartridge length, with faster burning powders and higher chamber pressures, allowing it to be used in more compact autoloading pistols and submachine guns. Because of this, the .45 ACP is superior to the .45 Colt for military purposes.
The designation ".45 Long Colt" originated amongst military personnel to prevent confusion with the smaller .45 Schofield. It has become a widely used alternative name for the cartridge, and adopted by Colt for use in designating the chambering in its own Single Action Army revolvers.