Chief EG-X
From Halopedia, the Halo wiki
File:L 46490758bebe86a15a660ab90633e3dc.jpg
Pic of the Bullet Casing
In Halo 3, if you play a multiplayer match, and then fire a bullet and pause the video afterwards, fly over to the casing, and look at the back of it. It says Chief EG-X. this is on the Battle Rife, Assault Rife, Pistol, and probably others.
