This HK USP uses a single 12 gram CO2 cartridge to power its was through mag after mag of BBs, with velocities in the field safe 330 FPS range.  The magazine holds 18 6mm BBs per full load. This USP is ready to go to work out of the box or with the muzzle accessory of your choice.
CO2 Blowback Action
Adjustable Hop-Up
18 Round Capacity Drop Free Magazine
DA/SA
330 FPS with .20 gram BB
Threaded Muzzle 14mm CCW
Magazine SKU Number 2275045
Notes: The Elite Force HK USP CO2 takes magazine part number 2275045 and uses rebuild kit 2211172