Here's some more info on the .50 GI
Specifications
Case type Rebated, straight
Bullet diameter .515 in (13.1 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)
Ballistics
* 300 gr (19 g) JFP, 700 ft/s, 350 ft-lbf
* 275 gr (18 g) JHP, 900 ft/s, 495 ft-lbf
* 300 gr (19 g) JHP, 860 ft/s, 493 ft-lbf