.45 GAP

The .45 G.A.P. (often called the .45 "GAP") pistol cartridge was designed by Ernest Durham, an engineer with CCI/Speer, at the request of firearms manufacturer Glock to provide a cartridge that would equal the power of the .45 ACP but was shorter to fit in a more compact handgun, and with a stronger case head to reduce the possibility of case neck blowouts. G.A.P. is an acronym for "Glock Automatic Pistol", and the .45 G.A.P. is the first commercially introduced cartridge identified with Glock.

Development
The .45 GAP has the same diameter as the .45 ACP pistol cartridge, but is slightly shorter, and uses a small-pistol primer instead of the large-pistol primer most commonly used in .45 ACP ammunition. Originally, the maximum bullet weight of the .45 GAP was 200 gr. In order to provide terminal ballistics on par with the standard 230 gr .45 ACP loads, the .45 GAP was designed to operate at a higher standard pressure—roughly equivalent to the higher pressures found in .45 ACP "+P" rounds. Since the .45 GAP has a much smaller cartridge volume than the .45 ACP, the desired pressure and resulting velocity needed to be achieved through powder selection alone. Later development concluded that the .45 GAP could in fact fire 230 gr ammunition just as the .45 ACP.

Glock .45 GAP pistols
The full-size Glock 37 pistol was introduced by Glock to use the .45 GAP cartridge and was followed by the compact Glock 38 and the subcompact Glock 39. The width of all three pistols is listed by the manufacturer as 1.18", compared with 1.27" for the .45 ACP Glock 21 and Glock 30, indicating that Glock was able to not only shorten the front to back size of the grip, but also the grip width. Glock's .45 GAP sized pistols utilize the same frame as their 9mm/.40cal/.357SIG line of pistols. The slide is slightly wider to accommodate the larger diameter .45 cal round and is flush with the frame. Magazines for the .45 GAP are the same dimensions as those used by the 9mm/.40/.357sig line of pistols.

Law enforcement application
Five state law enforcement agencies have adopted the .45 G.A.P. as a replacement to their current issue 9×19mm Parabellum (New York) or .40 S&W service handguns (Georgia, Pennsylvania, South Carolina, and Florida). The New York State Police, Georgia State Patrol, Pennsylvania State Police, South Carolina Highway Patrol, and Florida Highway Patrol have all adopted the Glock 37 and .45 G.A.P.

Initially, due to its acceptance by law enforcement and the popularity of subcompact handguns for concealed carry, a small number of manufacturers decided to produce pistols chambered in .45 G.A.P., including some Para-Ordnance M1911s and the Springfield Armory XD. Para has since dropped the G.A.P. Springfield Armory's XD pistol is listed in several different 45 G.A.P. varieties on their web site but they no longer produce any pistols in that caliber. Only Glock continues to manufacture pistols in the 45 G.A.P. cartridge.