.40 Smith & Wesson

.40 S&W
An expanded hollow point bullet (left) and an unfired hollow point .40 S&W cartridge
Type	Pistol
Place of origin	United States
Production history
Designer	Bob Klunk
Designed	January 17, 1990
Produced	1990–present
Specifications
Parent case	10mm Auto
Case type	Rimless, Straight
Bullet diameter	.400 in (10.2 mm)
Neck diameter	.423 in (10.7 mm)
Base diameter	.424 in (10.8 mm)
Rim diameter	.424 in (10.8 mm)
Rim thickness	.055 in (1.4 mm)
Case length	.850 in (21.6 mm)
Overall length	1.135 in (28.8 mm)
Case capacity	19.3 gr H2O (1.25 cm3)
Rifling twist	1 in 16 in. (406 mm)
Primer type	Small pistol
Maximum pressure	35,000 psi (240 MPa)
Ballistic performance
Bullet mass/type Velocity Energy 10.69 g (165 gr) Federal FMJ 1,130 ft/s (340 m/s) 468 ft·lbf (635 J) 7.45 g (115 gr) Cor-Bon Glaser 1,400 ft/s (430 m/s) 500 ft·lbf (680 J) 10.04 g (155 gr) Federal HST 1,160 ft/s (350 m/s) 463 ft·lbf (628 J) 8.74 g (135 gr) Underwood JHP 1,400 ft/s (430 m/s) 588 ft·lbf (797 J) 12.95 g (200 gr) Doubletap FMJ FP 1,050 ft/s (320 m/s) 490 ft·lbf (660 J)
Test barrel length: 4 inches (100 mm) Source(s):

The .40 S&W (10×22mm Smith & Wesson in unofficial metric notation) is a rimless pistol cartridge developed jointly by major American firearms manufacturers Smith & Wesson and Winchester. The .40 S&W was developed from the ground up as a law enforcement cartridge designed to duplicate performance of the Federal Bureau of Investigation's (FBI) reduced-velocity 10mm Auto cartridge which could be retrofitted into medium-frame (9mm size) semi-automatic handguns. It uses 0.40-inch (10 mm) diameter bullets ranging in weight from 105 to 200 grains (6.8 to 13.0 g).

In the aftermath of the 1986 FBI Miami shootout, in which two FBI special agents were killed and five wounded, the FBI started the process of testing 9×19mm Parabellum and .45 ACP ammunition in preparation to replace its standard-issue revolver with a semi-automatic pistol. The semi-automatic pistol offered two advantages over the revolver: 1) increased ammunition capacity and 2) increased ease of reloading during a firefight. The FBI was satisfied with the performance of its .38 Special +P 158 gr (10.2 g) L.S.W.C.H.P. (lead semi-wadcutter hollowpoint) cartridge ("FBI Load") based on decades of dependable performance. 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 series of practically oriented tests involving eight test events that they believed reasonably represented the kinds of situations that FBI agents commonly encounter in shooting incidents.

During tests of the 9×19mm and .45 ACP ammunition, the FBI Firearms Training Unit's Special Agent-in-Charge John Hall decided to include tests of the 10mm cartridge, supplying his personally owned Colt Delta Elite 10mm semi-automatic, and personally handloaded ammunition. The FBI's tests revealed that a 170–180 gr (11.0–11.7 g) JHP 10mm bullet, propelled between 900–1,000 ft/s (270–300 m/s), achieved desired terminal performance without the heavy recoil associated with conventional 10mm ammunition (1,300–1,400 ft/s (400–430 m/s)). The FBI contacted Smith & Wesson and requested it to 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 with the FBI, S&W realized that downsizing the 10mm full power to meet the FBI medium velocity specification meant less powder and more airspace in the case. They found that by removing the airspace they could shorten the 10mm case enough to fit within their medium-frame 9mm handguns and load it with a 180 gr (11.7 g) JHP bullet to produce ballistic performance identical to the FBI's reduced-velocity 10mm cartridge. S&W then teamed with Winchester to produce a new cartridge, the .40 S&W. It uses a small pistol primer whereas the 10mm cartridge uses a large pistol primer.