New Shooter’s Guide: 45 Colt vs. 45 Long Colt vs. 45 ACP

A lot of shooting terms are confusing because similar language can be used for very different things. One of the most confusing are cartridge names, such as 45 Colt, 45 Long Colt, and 45 ACP, where “ACP” is an abbreviation for Automatic Colt Pistol.

The confusion probably comes from the shorthand use of “45 Colt” for “45 Automatic Colt Pistol.” The latter is a mouthful, and a breezy way to name the cartridge your 1911 pistol fires is to call it a “45 Colt.” Also, because many early 1911s were of Colt manufacture, calling a 1911 pistol “45 Colt” made shorthand speaking sense.

But that would be a mistake. Better to say “45 Automatic” or “45 Auto” instead.

Also, some people call the “45 Colt” cartridge the “45 Long Colt” as the name to remove any confusion between “45 Colt” and “45 Auto.” But the “45 Colt” and the “45 Long Colt,” or “45 LC,” are the same cartridge, whereas the “45 Colt” and “45 Auto” are not the same.

Handgun cartridges are divided into three major types: those intended for semi-automatic pistols, those to be used in revolvers, and those for single-shot pistols. Those designed for semi-automatic pistols are either rimless or semi-rimmed to facilitate feeding from a magazine. Revolver cartridges are, in general, of rimmed construction, although some revolvers have been made to handle semi-rimmed or rimless cartridges, according to Cartridges of the World 17th Edition (COTW). 

The 45 Colt (aka the 45 Long Colt) and 45 ACP cartridges (not calibers, as a lot of shooters call them) are more than 100 years old, according to COTW. 

Dimensionally, the 45 Colt/45 Long Colt and 45 Auto are very different, making it unlikely that a round for one gun could be used in the other. The main difference is the 45 Colt/45 Long Colt is a rimmed straightwall revolver cartridge, whereas the 45 Auto is a rimless straightwall round. 

The 45 Colt/45 Long Colt has a case length of 1.29 inches and an overall cartridge length of 1.60 inches, compared to the 45 Auto’s case length of .898 inches and an overall cartridge length of 1.17 inches. The 45 Colt/45 Long Colt takes a bullet diameter of .454 compared to .452 for the 45 Auto. 

According to COTW, the 45 Automatic Colt Pistol (45 ACP) cartridge was developed by John Browning in 1905 and adopted by the United States Ordnance Department, with the Colt-Browning automatic pistol in 1911.

The 45 Automatic is the most powerful military handgun cartridge in use today. Several submachine guns have used it. The 45 Auto was replaced in 1985 as the official U.S. military handgun cartridge by the 9mm Parabellum. 

Similar cartridges to the 45 Automatic include:

• The 45 Automatic Match cartridge, which is a variation of the 45 ACP that’s shorter and has a reduced powder load. 
• The 45 Super, which is externally and dimensionally identical to the .45 ACP,  but is designed to be used in semi-auto pistols with stronger recoil springs and a shock buffer. The 45 Super case wall is thicker and is loaded to higher pressures than 45 ACP loads. 
• The 450 SMC (Short Magnum Cartridge or 450 Small Magnum Cartridge). It is basically a 45 Super with a small primer pocket. The 450 SMC uses a small magnum rifle primer rather than the standard large pistol primer of the .45 ACP.
• The 45 Auto Rim also confuses many shooters because of its similar name to the 45 Automatic. Also, its history creates confusion for some, even though it’s not loaded commercially today. The 45 Auto Rim’s history began in World War I, when both Colt and Smith & Wesson manufactured revolvers for the 45 Automatic cartridge. This required use of a half-moon clip to support and then eject the rimless 45 Automatic rounds. Thousands of these revolvers were sold on the civilian market after the war ended. In 1920, the Peters Cartridge Co. introduced a rimmed version of the 45 Automatic, which eliminated the need for half-moon clips in the revolver.

The 45 Colt, also called the 45 Long Colt by some manufacturers to reduce confusion with 45 Automatic loads, is even older than the 45 Auto. The 45 Colt was introduced in 1873 by Colt as one of the cartridges for its famous Peacemaker single-action revolver, Cartridges of the World reports. Both the cartridge and the revolver were adopted by the U.S. Army in 1875.

The 45 Colt/45 Long Colt is one of the most famous American handgun cartridges and is still a favorite with big-bore advocates. It served as the official handgun cartridge of the Army until 1892, when it was replaced by the 38 Long Colt. The 45 Colt was originally a blackpowder cartridge, loaded with 40 grains of FFg powder and a 255-grain lead bullet.

Similar loads to the 45 Colt/45 Long Colt include:

• The Cowboy 45 Special cartridge, which uses a case that is shorter (trim to .892 inch) for use with light loads in 45 Colt-caliber revolvers and lever guns for Cowboy Action Shooting. Shooting light loads with excessive airspace often causes case splits and tough extraction, according to Cartridges of the World. By using the Cowboy 45 Special case, with its 45 Colt rim and 45 Auto length, the problem of case splits is minimized so competitors have fewer failures due to brass problems.
• The obsolete 45 Colt Government combined the length of the Smith & Wesson Schofield revolver round with the rim of the Colt SAA cartridge. Army Ordnance described at least one version of this cartridge officially as Revolver Ball Cartridge, Caliber .45. The Remington-UMC version was labeled (on the box and case heads) as 45 Colt.
• The 45 Smith & Wesson cartridge was introduced in 1875 for the Smith & Wesson Schofield revolver. This revolver was adopted by the U.S. Army in that year and used until 1892, when it and the 45 Colt Army revolver were replaced by the Colt Army & Navy Model in 38 caliber. Ammunition for the 45 S&W can be used in most 45 Colt revolvers, but the reverse is not true.

Various importers offer excellent Italian-made replicas of the original Colt model, and Ruger and several other makes of more modern single-action revolvers are currently chambered in 45 Colt.

The 45 Colt is extremely accurate and is a popular field cartridge that can be safely handloaded to velocities in excess of 1000 fps with 250-grain cast bullets. Blackpowder revolvers should not be used with any load developing more than about 800 fps muzzle velocity.

To learn more about these and other cartridges, order Cartridges of the World 17th Edition here. Gun Tests Editor Todd Woodard has edited the last several editions of the famous cartridge book. Also, he’s the author of the Shooter’s Bible Guide to Cartridges, available here.