The .40 S&W cartridge has been called the “ideal cartridge for personal defense and law enforcement.”

The .40 S&W was specifically developed to duplicate performance of the FBI’s reduced-velocity 10mm cartridge and fit into medium-frame (9mm size) automatic handguns. It debuted January 17, 1990, along with the new Smith and Wesson 4006 pistol.

Ironically, the Glock 22 and Glock 23 pistols chambered in .40 S&W were announced a week before the 4006 and beat Smith & Wesson to the market in 1990, with the S&W cartridge. Clever marketing has S&W in the very name of the round. The new guns and ammunition were an immediate success.

Since the 1900’s, the .38, .45 and 9mm had been the main cartridges for law enforcement and the military in the United States. In the early 1970’s Whit Collins had a better idea. He wanted to rechamber the 9mm Browning Hi-Power in a more powerful cartridge.

Collins originally considered the .38 Super, but read Jeff Cooper’s concept of an ideal cartridge of a .40 caliber bullet weighing 200gr moving at 1,000fps. After much study of feeding geometry Collins began looking for existing rifle cases that had the right dimensions and could be trimmed to proper length a Browning Hi-Power magazine.

Cooper approved and helped Collins get his idea to Guns & Ammo. By 1972 a Browning Hi-Power chambered in .40 G&A was test fired. The loads being fired consisted of a 180gn bullet at 1,050fps out of the 5″ barrel.

In 1973 Cooper and Collins explored the idea of a longer cased .40 caliber round developed for large frame .45 platforms. Whit Collins continued working on his .40 G&A and Jeff Cooper began work on his .40 Super. In 1978 Cooper helped conceive the Bren Ten semiautomatic pistol, and his .40 Super evolved into 10mm Auto. Bren didn’t last long, but the 10mm would be re-born.

Bren 10 image from genitron.com

The genesis of the .40 S&W was on April 11, 1986 in Miami Dade county Florida. Eight FBI agents and two bank robbers engaged in a fight to the death.  FBI Special Agents Jerry L. Dove and Benjamin P. Grogan were killed, while five other agents were wounded.

The two robbery suspects, both with military experience, William Russell Matix and Michael Lee Platt, were also killed. These were bad men armed with a S&W M3000 12-gauge shotgun and a Ruger Mini-14.  They had decided they were not going to be taken alive.

The incident has been intensely studied by the FBI and other law enforcement agencies. Despite outnumbering the suspects 4 to 1, the agents found themselves pinned down by rifle fire and unable to respond effectively. Although both Matix and Platt were hit multiple times during the firefight, Platt fought on and continued to injure and kill agents.

The subsequent FBI investigation blamed the failure on the poor stopping power of their .38 and 9mm handguns. They started the process of testing 9mm and .45 ACP ammunition seeking to replace the 3″ barrel Smith and Wesson Model 13 with a semi-automatic pistol. The semi-automatic pistol offered increased ammunition capacity, and was easier to reload during a gunfight.

The FBI was satisfied with the performance of its .38 Special +P 158 gr cartridge. Ammunition for the new semi-automatic pistol had to deliver terminal performance equal or superior to the .38 Special FBI Load. The FBI developed a new series of practically oriented tests involving eight test events that reasonably represented the kinds of situations that FBI agents commonly encounter in shooting incidents.

The FBI ultimately selected a downloaded 10mm using a 180-grain jacketed hollow-point bullet fired at 950 fps. Even down loaded, this was a very hot load, unsuitable for the average agent.

It proved to be an excellent ballistic combination, although the long case was a problem. The 10mm round required a large-frame pistol.  At that time, there were only two manufacturers making large frames, S&W and Colt.

The FBI contacted Smith & Wesson and requested they design a handgun to FBI specifications, based on the existing large-frame S&W Model 4506 .45 ACP handgun, that would reliably function with the FBI’s reduced velocity 10mm ammunition.

During this collaboration, Smith & Wesson smart guys soon realized that downloading the 10mm to meet the FBI specifications meant less powder and more airspace in the case. They found that by removing the airspace they could shorten the 10 mm case enough to fit within their medium-frame 9mm handguns.

Working in a secret joint project with Winchester Ammunition they developed a ballistically identical cartridge to become known as the .40 S&W. When loaded with a 180 gr bullet, it produced the same ballistic performance as the FBI’s reduced velocity 10mm cartridge.

Other than a .142″ reduction in overall case length, resulting in less gunpowder capacity in the .40 S&W; the 10mm and .40 S&W are identical in projectile diameter, both using a 0.400″ caliber bullet. The .40 uses a small pistol primer whereas the 10mm cartridge uses a large pistol primer.

The Smith & Wesson 1076, chambered for the 10mm Auto round, was chosen by the FBI. In May 1997, the FBI officially adopted the Glock .40 S&W pistol for general agent use and today the Model 23 “FG&R” (finger groove and rail) is FBI issue.

The 40 S&W, has nearly identical accuracy with the 9mm but it has an energy advantage over the 9mm and more manageable recoil than the 10 mm Auto cartridge. The .40 S&W and the 9 mm Parabellum both operate at a 35,000 psi (240 MPa) SAAMI maximum, compared to a 21,000 psi (150 MPa) maximum for .45 ACP.

The .40 S&W became more popular than the 10mm due to the ability to chamber the shorter cartridge in standard frame automatic pistols designed initially for the 9 mm Parabellum. The problem here is that pistols designed for the 9mm are damaged by the high pressures and high energy of the .40 accelerating wear. Many shooters experience increased felt recoil often described as muzzle flip.

The .40 S&W has suffered a number of cartridge case failures, particularly in older Glock pistols. It is believed that the large area of unsupported case head in Glock barrels creates a weak spot. The feed ramp on the Glock .40 S&W pistols is larger than on other Glocks. Most of the failures have occurred with reloaded ammunition. These failures are commonly referred to as “kaBooms” or “kB!”.

While these case failures do not often injure the person holding the pistol, the venting of high pressure gas tends to eject the magazine out of the magazine well at a high rate of speed in a flamboyant fashion, and usually destroys the pistol. In some cases, the barrel will also fail, blowing the top of the chamber off.

Glock Kaboom

While the .40 S&W is far from being the only cartridge to suffer from case failures, it is more susceptible for a number of reasons. The .40 S&W works at relatively high pressures (35,000 psi/240 MPa SAAMI max). Since the .40 S&W is a wide cartridge and is often adapted to frames designed for the narrower 9x19mm cartridge, the length of the feed ramp must be longer to provide the same angle, which causes the feed ramp to extend into the chamber. This leaves more of the case head unsupported.

In late 1995, Federal Cartridge redesigned their .40 S&W cartridge cases to internally strengthen the case web. While Federal won’t discuss this, they don’t want Glocks to blow up with .40 cal Federal ammunition.

Writer Walt Rauch figured out that bullet set-back (caused by daily administrative loading) in the .40 S&W could raise pressures exponentially. Rauch, in a feature entitled Why Guns Blow Up! says: “The simple chambering and rechambering of a cartridge does push the bullet back into its case.”

Hirtenberg Ammunition Company of Austria (at the request of GLOCK, Inc.) determined that, with a .40 caliber cartridge, pushing the bullet back into the case 1/10 of an inch doubled the chamber pressure. This is higher than a proof load. This can occur with but one chambering since it is dependent on how well the case was crimped or sealed to the bullet.

The .40 has truly been the sword of a generation of cops. It was concieved by none other than Jeff Cooper himself and developed with some careful science. With improvements in 21st century ammo, it may be time to look ahead to the next big thing. The .40 S&W’s high pressure and sharp recoil make it unpleasant to shoot and hard on guns. As bullet technology develops, the differences between .40 S&W, 9mm and .45ACP become less significant.

The FBI’s announcement that they were leaving the .40 to go back to the 9mm has been taken by many as a sign that the .40  is obsolete. I believe that it will remain relavent and stay with us in home defense and law enforcement for some time to come.

Do your home work and your range work before picking a handgun caliber. When you do pick one, remember, it is rude to talk about politics, religion or handgun caliber at the supper table.