Successfully complete all missions on the Hardest difficulty setting to unlock the PX50 Bound Shot.
Successfully complete all missions on the Inferno difficulty setting to unlock the Genocide Gun.
Successfully complete all missions on the Hard difficulty setting to unlock the Y20 Impulse.
Successfully complete all missions on the Normal difficulty setting to unlock the ZE Launcher.
Accomplish the indicated achievement to get the corresponding number of Gamerscore points:
Successfully complete all missions on the Easy difficulty setting to unlock the Zero Laser Rifle.