ACP stands for “Automatic Colt Pistol” and refers to a specific type of cartridge developed by the ammunition manufacturer Colt for use in their semi-automatic handguns. The 45 ACP (Automatic Colt Pistol) cartridge is one of the most iconic pistol cartridges in history, having been used in classic firearms like the Colt M1911 pistol.
History of the 45 ACP Cartridge
The 45 ACP cartridge was developed by famous American gun designer John Browning in 1904 for Colt’s newly invented M1905 semi-automatic pistol. At the time, most handguns were revolvers that used heavy revolver cartridges like the 45 Colt. Semi-autos were gaining popularity though and required a rimless, straight-walled cartridge to function properly in their magazines and actions.
Browning’s 45 ACP design fit this need perfectly. It was based on a shortened version of the 45 Colt revolver round, retaining the large 45 caliber bullet but in a shorter, rimless case suited for semi-auto pistols. The “ACP” designation was to specify that it was for the new Colt semi-automatic pistol design.
The US Army first adopted the 45 ACP cartridge in 1911 when it ordered the iconic M1911 pistol to replace older revolvers. The combination of the M1911 pistol and 45 ACP creating an extremely effective military sidearm that served through both World Wars, Korea, and Vietnam. Even today, over 100 years since its introduction, the 45 ACP is still a popular and commonly available cartridge.
45 ACP Ballistics and Performance
Here are some key ballistic and performance characteristics of 45 ACP ammunition:
- Bullet Diameter: 0.452 inches
- Case Length: 0.898 inches
- Overall Length: 1.275 inches
- Common Bullet Weights: 185gr, 200gr, 230gr
- Standard Velocity: 830-900 fps
- Muzzle Energy: 350-450 ft-lbs
The 45 ACP is a moderate to low-velocity cartridge designed for excellent stopping power at short combat ranges under 50 yards. While not a magnum pistol round, it still produces a large permanent wound cavity and deep penetration thanks to its heavy, slow-moving 230 grain bullets. The 45 ACP proved itself in battle for over 50 years as a manstopper round.
The 45 ACP operates at relatively low pressures compared to many other semi-auto pistol rounds. This helps reduce wear and tear on pistols and extends their service life. It’s often said that the 45 ACP allows for “shooting major caliber bullets with minor caliber wear” on guns.
Popular Uses of 45 ACP Pistols and Ammo
Here are some of the most popular uses for 45 ACP chambered pistols and ammunition:
- Self-Defense/Concealed Carry – The 45 ACP is an excellent choice for self-defense due to its stopping power. Modern compact 45’s can be easily concealed.
- Tactical/Police Use – Military, police, and SWAT units utilize 45 ACP pistols and SMGs for its reliability and terminal ballistics.
- Competition Shooting – The 45 ACP caliber has its own division in IPSC/USPSA competitive shooting sports.
- Hunting – Effective on medium game like hogs, deer, or black bear at short distances when using expanding bullets.
The 45 ACP hits with authority and its low pressures and heavy bullets make it very controllable in rapid fire. For over 100 years, the 45 ACP has proven itself as an extremely effective defensive and tactical pistol cartridge.
45 ACP Pistol Examples
Here are some of the most iconic and popular pistols chambered for the 45 ACP cartridge:
- Colt M1911 – The original 45 ACP pistol adopted by US Army in 1911. The quintessential 45 pistol.
- M1911A1 – Slightly updated variant used through WWII, Korea, and Vietnam.
- Browning Hi-Power – Classic high-capacity 9mm design also available in 45 ACP.
- Glock 21 – A 45 ACP version of the popular polymer-framed Glock pistols.
- SIG Sauer P220 – DA/SA 45 ACP pistol carried by many police and federal agencies.
- Heckler & Koch USP45 – 45 caliber version of the USP pistol family used by special forces groups.
- Smith & Wesson M&P45 – Polymer-framed pistol offered in 45 ACP.
Many other pistol makers like Beretta, CZ, Springfield Armory, and FN also offer 45 ACP models. The cartridge has maintained steady popularity on the civilian market as a self-defense round, keeping demand and options plentiful for new 45 ACP handguns.
45 ACP Ammunition Types
Here are some of the different types of 45 ACP ammunition commonly available:
- Full Metal Jacket (FMJ) – Inexpensive range ammo with a lead core bullet enclosed in a copper jacket. Minimal expansion.
- Total Metal Jacket (TMJ) – Fully enclosed bullet with no exposed lead. Used where lead bullets are prohibited.
- Jacketed Hollow Point (JHP) – Lead bullet with a hollow cavity in the nose to provoke expansion. For self-defense use.
- Semi-Wadcutter Hollow Point (SWHP) – Flat-nosed bullet with hollow point cavity. Reduced recoil.
- Frangible – Bullets designed to fragment upon impact. Used for training and in sensitive environments.
There are also 45 ACP rounds designed specifically for subsonic velocities, match accuracy, and specialty applications like law enforcement or military use. Overall, the 45 ACP can utilize a very wide variety of bullet styles and loadings.
Reloading 45 ACP Ammunition
The 45 ACP cartridge is very commonly handloaded and reloaded. Here are some key factors for reloading 45 ACP rounds:
- Uses both large and small pistol primers interchangeably
- Wide range of usable powders like Titegroup, Winchester 231, Vihtavuori N340, Accurate #5, etc
- Bullets from 165gr to over 260gr
- Overall length must stay within 0.898 – 1.275 inches
- Case can be reused many times
- Lower pressure round allows more reloading flexibility
Reloading the 45 ACP allows shooters to customize their ammunition at reduced cost. Handloads can be assembled for plinking, training, matches, self-defense, hunting, or specialty needs. The 45 ACP’s relatively simple specifications and low pressures make it quite beginner friendly to reload.
Pros and Cons of 45 ACP Pistols and Ammo
Here are some of the main pros and cons of using 45 ACP pistols and ammunition:
Pros
- Excellent stopping power and penetration from heavy bullets
- Very controllable and soft-recoiling due to low pressures
- Proven real world performance in military/law enforcement use
- Naturally subsonic velocity helpful for suppression
- Low pressure extends service life of pistols
- Abundant ammo selections and availability
Cons
- Large pistol grip required to accommodate thick cartridge
- Lower magazine capacities than comparable smaller rounds
- Bulky and heavy ammo less convenient for carry
- Slower velocities than many other defensive rounds
- Less suitable for long range accuracy shooting
Conclusion
In summary, 45 ACP refers to a specific straight-walled, rimless .45 caliber pistol cartridge designed by John Browning in 1904 for use in Colt’s semi-automatic handguns. It gained worldwide fame and adoption after being selected as the official US military pistol cartridge in the iconic M1911 pistol used through countless 20th century conflicts.
The 45 ACP’s unique combination of controllable recoil, excellent stopping power at close ranges, and reliable functioning in pistols has maintained its popularity over 100 years after its creation. It continues to serve defensive pistol users and competitors, law enforcement officers, special forces groups, and civilian shooters around the world.
While not as fast or flat shooting as many newer pistol rounds, the 45 ACP’s proven track record and continued availability makes it a staple cartridge for full-size semi-auto pistols the world over. When loaded into a quality firearm, 45 ACP ammo delivers unmatched power and terminal performance that still defines what a real pistol cartridge should be.