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What is the Difference Between the .45 ACP and the .45 GAP Bullets?

What is the Difference Between the .45 ACP and the .45 GAP Bullets?

When you think of .45 caliber, you are most likely imagining the .45 ACP cartridge. This is, after all, the quintessential .45 caliber semi-automatic pistol cartridge.

In 2003, Glock collaborated with the ammunition manufacturer CCI-Speer to introduce a new cartridge, the .45 GAP, with the purpose of creating a .45-caliber cartridge that could fit in a more compact handgun frame than .45 ACP.

There are several reasons behind the .45 GAP’s creation and differences between the cartridges.

.45 ACP: The Fightin’ .45

To better understand why the .45 GAP exists, it’s essential to know a brief history of its predecessor, the .45 ACP.

The .45 ACP cartridge was designed in 1904 by the legendary John Moses Browning, at the behest of the U.S. military, then engaged in the Philippine-American War.

In the aftermath of the Moro Rebellion at the turn of the 20th century, the U.S. Cavalry’s then-current issued .38 Long Colt revolver cartridge was judged too inefficient against the Juramentado warriors, who continued charging toward American troops even after they had been shot multiple times.

Following these events, the 1904 Thompson-LaGarde tests were conducted, during which various handgun cartridges were tested. With full metal jacket projectiles, .45-caliber ammunition creates larger wound cavities than equivalent .30 or .38 caliber ammunition. The Army and the Cavalry observed the results and determined that the next handgun cartridge should be at least .45 caliber.

The same year, John Browning was working on a prototype .41 caliber pistol and cartridge. When the Cavalry asked for a .45 caliber equivalent in 1905, these prototypes were modified, resulting in the .45 Automatic Colt Pistol (.45 ACP) cartridge. The first .45 ACP pistol was the Colt Model 1905, an enlarged version of the .38 ACP Colt Model 1902.

In its original specification, the .45 ACP bullet has a nominal diameter of 0.452”, a bullet weight of 230 grains, and a case length of 0.898”. When fired out of a 5” barrel, the muzzle velocity is approximately 850 ft/s, resulting in a muzzle energy of about 369 foot-pounds force. These specifications were later standardized by SAAMI, under the name .45 Automatic (or .45 Auto).

Following the recommendations of U.S. Army Colonel John T. Thompson, who suggested that the next service pistol be a .45 caliber semi-automatic pistol to replace the existing .38 and .45 revolvers, the 1907 Army Pistol Trials were conducted. Colt entered the competition with one of John Browning’s pistol designs, eventually winning them. This pistol was then formally adopted by the U.S. Army, receiving the M1911 designation.

The U.S. military used .45 ACP as a standard service cartridge from 1911 to 1985, when the 9mm Beretta M9 replaced the M1911A1. With over seven decades of military service, including combat use in both World Wars, the Korean War, and the Vietnam War, the “Fightin’ .45” earned its reputation as an effective man-stopping cartridge.

Among civilians, it gained tremendous popularity as a personal defense and competition shooting cartridge, which it continues to enjoy. There is a wide selection of .45 ACP firearms available for concealed carrying, such as the Smith & Wesson M&P45 Compact, the Kahr P45, the SIG P250 Compact, and the many compact versions of the 1911 pistol.

Even criminals are no strangers to the effectiveness of the .45 ACP. American gangsters of the Prohibition Era such as Al Capone or “Baby Face” Nelson, Bonnie and Clyde, Machine Gun Kelly, and even France’s Public Enemy No. 1 Jacques Mesrine all used or favored .45 ACP firearms.

The .45 ACP was and still is a popular pistol cartridge, with decades of proven effectiveness.

.45 GAP: An Alternative?

By the turn of the 21st century, other than the .45 ACP and direct derivatives, such as .45 Super or .460 Rowland, there were virtually no other successful .45-caliber pistol cartridges intended for use in duty pistols.

Believing there was a potential opening in the market of self-defense pistols, the Austrian firearms manufacturer Glock partnered with CCI-Speer in 2003 to develop a new cartridge, the .45 Glock Automatic Pistol (.45 GAP).

The .45 GAP cartridge is intended to replicate a modern .45 ACP cartridge’s performance, but with a modern case design and propellants.

Although capable of using the same 230-grain bullets as .45 ACP, this bullet weight is considered to be at the upper limit of what .45 GAP can handle. This cartridge is better suited for lighter bullet weights, such as 185 or 200 grains.

Real-world Performance Comparison

Pistols chambered in .45 ACP are typically larger than those chambered in 9x19mm or .40 S&W because they must fit the large cartridge and feed it reliably.

In theory, the .45 GAP offers performance equivalent to that of .45 ACP but using a shorter case (0.760”). This allows it to be used in pistols with a 9mm or .40 frame size.

A typical .45 GAP cartridge is fitted with a 200-grain bullet, delivering a muzzle velocity of 1000 ft/s out of a 4.5” barrel, resulting in a muzzle energy of 444 foot-pounds force. On paper, this is equivalent to .45 ACP +P (increased pressure).

Law enforcement agencies such as the New York State Police and the Florida Highway Patrol tested .45 GAP firearms such as the Glock 37. Officers remarked they were, on average, more accurate with these pistols than with equivalent .45 ACP models like the Glock 21. Shooters of smaller stature were able to hold and grip the G37 more easily.

These initial first impressions resulted in the adoption of .45 GAP by some state and local law enforcement agencies. Almost all adopted the full-size Glock 37 and its subcompact version, the Glock 39, as their new duty and back-up pistols.

Rise and Fall of the .45 GAP

Soon, other manufacturers introduced their own .45 GAP firearms, such as the .45 GAP version of the Springfield XD or the Para-Ordnance CCO-GAP. It seemed as though the new caliber had a bright future.

However, as new developments in handgun technology continued, new models in .45 ACP featuring shorter, more comfortable frames were introduced. The new Smith & Wesson M&P45 and Glock’s G21SF seemed to have alleviated the problem of large grip sizes, competing with the .45 GAP.

These new handguns contributed to decreased interest in the .45 GAP cartridge, but ammunition shortages impacted it more. The shortage began in 2008 with a rise in gun sales after the 2008 Presidential election. After the Sandy Hook shooting in 2012, the fear of more gun control laws led to even more ammunition and firearm sales, creating plenty of demand with a short supply.

Before this shortage, the number of manufacturers producing .45 GAP ammunition was already limited. When supply issues made ammunition in this caliber impossible to find, it didn’t take long for its adopters to switch to something that would be available during an ammo drought.

Virtually all the police agencies that once adopted the .45 GAP eventually returned to .45 ACP or transitioned away from .45s, adopting 9mm or .40 S&W instead.

The most common reason for switching is the preference for a more readily-available and proven round. Others cited the need for higher capacity; the Glock 37 only holds 10+1 rounds. In comparison, the .45 ACP Glock 21 has a capacity of 13+1 rounds, the .40 S&W Glock 22 has 15+1, and the 9mm Glock 17 carries up to 17+1.

Other manufacturers abandoned their .45 GAP offerings, leaving Glock as the only remaining manufacturer of .45 GAP firearms. The Glock 37 was updated to Gen 4 in 2010, making it the last .45 GAP introduced on the market.

Whether the .45 GAP was unnecessary or simply misunderstood remains up for debate. As Paul Harrell would say: You be the judge.

The Bottom Line

The .45 GAP was intended to make .45-caliber handguns more compact and accessible to shooters of all sizes, without compromising on the performance that made .45 ACP attractive to use. While it did deliver on the performance, a perfect storm of technological developments and unfortunate circumstances rendered it obsolete within a decade of its introduction.

For more information about holsters for your Glock, 1911, or any other pistols and handguns, we offer a wide variety of styles and prints to fit your needs. Contact We the People Holsters at (866) 998-6191 with any questions regarding the ideal holster for your firearm.