The .50 GI pistol cartridge was developed by Vic Tibbets and Alex Zimmermann of Guncrafter Industries. The .50 GI was introduced at the 2004 SHOT Show alongside the Guncrafter Industries Model No. 1, a variation of the M1911. The round has a rebated rim that is the same diameter as that of the .45 ACP. This allows the larger cartridge to be chambered in an existing .45 ACP firearm by simply switching the barrel, rather than a full upper replacement.
In 2006, Guncrafter Industries introduced its 1911 Model No. 2 which sports a full length light rail/dust cover and is chambered for the 50 GI cartridge.
Both the M1 and the M2 can be fitted with Guncrafter Industries' .45 ACP conversion unit, the .45 ACP magazines hold 8 rounds.
Physically, the .50 GI round is slightly shorter than the .45 ACP but is wider. A magazine can hold 7 rounds.
The .50 GI operates at pressures comparable to the .45 ACP, around 15,000 psi (100 MPa). Interestingly, felt recoil is also similar to the .45 ACP. Also, the .50 GI is moderately accurate bullet. The 300 grain (19 g) JFP (jacketed flatpoint) produces a 25-yard group of 2.24 inches, and the 300-grain JHP (jacketed hollowpoint) and 275-grain JHP produce a 25-yard group of only 1.14 inches.
The penetration and delivered energy of this slower round is about the same as a .40 Smith and Wesson and .45 ACP cartridge. Despite its .50 Caliber classification, it is a far cry from the .50 Action Express and .500 S&W Magnum; however, it offers the practical use of a large caliber projectile never before seen in a semiauto handgun. Impact force ranges from .40 Smith and Wesson to near lighter .357 Magnum rounds, but do not break the 500 ft·lbf mark at recommended pressure loadings. This might be possible in a longer barreled 1911, but since only 2 models which chamber the cartridge exist, custom machining and hand loading would be necessary.
The cartridge is mainly used in independent law enforcement and personal defense, but its high cost and limited availability hamper widespread use. Currently, the only commercial handguns available chambered in the round are Guncrafter Industries' own Colt 1911 handgun variants, and the high cost and limited manufacture of these models limits their availability as issued sidearms in both military and law enforcement. To this date, no known state or federal agency currently uses the weapon, but there were talks of it being evaluated by the FBI for field testing when the cartridge was initially released.