A .50 GI next to a .45 ACP cartridge.
|Place of origin||United States|
|Designer||Vic Tibbets / Alex Zimmermann|
|Case type||Rebated (RB), straight|
|Bullet diameter||.500 in (12.7 mm)|
|Neck diameter||.526 in (13.4 mm)|
|Base diameter||.526 in (13.4 mm)|
|Rim diameter||.480 in (12.2 mm)|
|Case length||.899 in (22.8 mm)|
|Overall length||1.221 in (31.0 mm)|
The .50 GI (12.7×23mmRB) 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.
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. The M1 and M2 magazines can hold seven rounds. The Glock conversion can hold eight rounds in the standard magazine and nine with the extended base pad.
The .50 GI operates at pressures comparable to the .45 ACP, around 15,000 psi (100 MPa). Felt recoil is not unlike that of the .45 ACP. The .50 GI has developed a reputation for accuracy, though this may be due to the high precision of the semi-custom and very expensive Guncrafter pistols themselves. In one test, the 300 grain (19 g) jacketed flatpoint (JFP) gave a 25-yard group of 2.24 inches, and the 300-grain Jacketed hollow point (JHP) and 275-grain JHP gave a 25-yard group of 2.14 inches.
The penetration in gelatin (but not necessarily the kinetic energy) of the .50 GI is significantly different than the .45 ACP. While it is one of the few examples of the largest caliber projectile (.50) in a semiauto handgun it was purpose built to have a recoil impulse and kinetic energy substantially less than the magnum .50 caliber rounds such as the 50 Action Express (semiautomatic) or .500 S&W Magnum (revolver). Factory loaded ammunition has a kinetic energy of around 500 ft·lb.
In one evaluation the following performance difference was noted between the .45 ACP and the .50 GI: "It actually pounded my steel target with so much force that it knocked the entire 100-pound plate and stand combo hard enough to make it furrow the ground it stood upon.[...]Folks, these .50 calibers really do hit that hard. [The 300 grain TMJ] caused dings in steel targets that normally fracture .40 and .45 cal rounds into so much dust." 
The cartridge is not used in law enforcement and rarely for personal defense due to limited availability of ammunition and guns chambered for the cartridge. Currently, the only commercial handguns available in this caliber are Guncrafter Industries' own Colt 1911 handgun variants and its Glock 21 / Glock 20 conversion upper, and Magnum Research chambers their BFR revolver in this caliber on a custom basis.
- 185 gr (12 g) JHP, 1200 ft/s, 591 ft-lb, 222 Power Factor
- 275 gr (18 g) JHP, 900 ft/s, 495 ft-lb, 248 Power Factor
- 300 gr (19 g) JFP, 700 ft/s, 350 ft-lb, 210 Power Factor
- 300 gr (19 g) JHP, 860 ft/s, 493 ft-lb, 258 Power Factor
- .45 ACP
- .50 Action Express
- .500 S&W Magnum
- .50 caliber handguns
- List of firearms
- List of handgun cartridges
- 12 mm caliber
- 50GI Proprietary
- "Loading the .50GI" by Charles E. Petty in American Handgunner, Sept-Oct 2004
- "Title Unknown". Archived from the original on 2009-09-21. Retrieved 2009-09-19.
- "Tactical-Life.com » Combat Test: G.I. GLOCK 21 .50". Archived from the original on 2009-09-21. Retrieved 2009-09-19.
- "Bowen's .50 GI Revolver - The .50GI Forums". Archived from the original on 2009-09-21. Retrieved 2009-09-19.
- Anderson, Dave (September 2007). "Bye Bye .45". Guns (FMG Publications): 48–53.