.45 ACP

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The .45 ACP (Automatic Colt Pistol) pistol cartridge was designed by firearms designer John Browning. Based upon his earlier .380 ACP pistol cartridge, the .45 ACP was introduced along with Colt M1911 pistol adopted by the US Army in 1911. The round was later used in several submachine guns.

1 Design
2 Performance
- 2.1 Muzzle velocity
3 Load variants
4 Synonyms
5 Firearms using the .45 ACP
6 See also
7 External links

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Design

Image:45caliberACP.jpg The US Cavalry began looking in the early 1900s for a replacement for their revolver, which was a .45 Colt Single Action Army. The Cavalry had fielded some double action revolvers in .38 Long Colt, and they determined that the .38 caliber round was significantly less effective against determined opponents, such as the Moro warriors they were fighting at the time, than the .45 Colt. Because of this, the Cavalry decided that a minimum of .45 caliber was required in the replacement handgun. It had also been determined that a .44-caliber bullet was the smallest diameter suitable for putting a wounded horse out of its misery. Colt had been working with Browning on a .41 caliber cartridge in 1904, and in 1905 when the Cavalry asked for a .45 caliber equivalent, Colt modified the pistol design to fire a .45 caliber version of the prototype .41 caliber round. The original round that passed the testing fired a 200 grain (13 g) bullet at 900 ft/s (275 m/s), but was later changed to a 230 grain (15 g) bullet at about 850 ft/s (260 m/s). The resulting .45 caliber cartridge, named the .45 ACP, is similar in performance to the .45 S&W cartridge, and only slightly less powerful (but significantly shorter) than the .45 Colt cartridges the Cavalry was using. Modern propellants have boosted the .45 ACP well beyond the power and velocity of the original .45 Colt, though modern .45 Colt loads are also far beyond the original loadings.

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Performance

The result is one of the world's more effective combat pistol cartridges, one that combines very good accuracy and stopping power for use against human targets. The cartridge also has relatively low muzzle blast and flash, as well as moderate recoil. Like most pistol cartridges, it is a low-velocity round, and thus not effective against body armour. Another drawback for large-scale military operations is the bullet's large size and greater material costs in manufacturing compared to the 9 mm Luger cartridge.

Even in its full metal jacket form the .45 ACP cartridge has a reputation for effectiveness against human targets, because its large bullet creates a deep and substantial permanent wound channel. Hollow-point configurations increase the expansion and energy-transfer potential of the round, causing it to be even more deadly.

Being a moderate-powered round on the energy scale, .45 ACP bullets have little tendency to overpenetrate, which otherwise results when a projectile passes through an intended target with enough velocity to injure another person. The combination of stopping power and controlled penetration makes the .45 ACP practical for police use. Many US hostage rescue teams prefer the .45 ACP because of these qualities.

Today most of the U.S. military uses the 9 mm Parabellum cartridge, but the accuracy of the .45 ACP cartridge has ensured its continued popularity with large caliber sport shooters. Many US Special forces and police units (such as the Army's Delta Force, Navy Seals and Air Force Para Rescue) still use this round in the form of modified 1911A1s and Heckler & Koch's SOCOM Mk. 23s and USP Tacticals.

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Muzzle velocity

14.7 g (230 gr) Full Metal Jacket: 260 m/s (860 ft/s)
11.9 g (185 gr) CCI/Speer Gold Dot JHP (from 5in (127 mm) barrel): 317 m/s (1041 ft/s)
14.7 g (230 gr) Federal Hi-Shok JHP (from 5 in (127 mm) barrel): 260 m/s (860 ft/s)

+ P loads

11.9 g (185 gr) JHP: 350 m/s (1150 ft/s)
14.7 g (230 gr) JHP: 290 m/s (950 ft/s)

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Load variants

Several manufacturers market pre-loaded .45 ACP rounds in sizes ranging from 117 to 230 (90 in the case of Le mas RBCD) grains (8 to 15 g), with the most popular commercial load being the standard military loading of a 230 grain (15 g) FMJ bullet at around 850 ft/s (260 m/s). Specialty rounds are available in weights under 100 grains (6.5 g) and over 260 grains (16.8 g); popular rounds among reloaders and target shooters include 185 and 230 grain (12 and 15 g) bullets. Hollowpoint rounds intended for maximum effectiveness against live targets are designed to expand upon impact with soft tissue, both increasing the energy transferred from the round to the target and enhancing the wound-creating power of the expanded round.

Most ammunition manufacturers also market what are termed "+P" loadings in pistol ammunition, including the .45 ACP. This means the cartridge is loaded to a somewhat higher maximum pressure level than SAAMI standard, generating more velocity and muzzle energy. This a common practice for updating older cartridges to match the better quality of materials and workmanship in modern firearms.

The terminology is generally given as ".45 ACP +P", "9mm Luger +P", ".38 Special +P", etc., and appears on the headstamp. It is important to note that +P cartridges are dimensionally identical to standard-pressure one and will chamber and fire in all firearms designed for the standard-pressure loadings. +P loadings should not be used in firearms not specifically designed for them as they are harder on the gun and may cause damage and injuries.

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