The USAS 12 is unlocked at level 4, as soon as Create-A-Class is available. The USAS 12 is fully automatic, but has a very low rate of fire compared to the AA-12 and every other automatic weapon; however, it has much more carried ammunition (36 total rounds as opposed to 16). The USAS 12 has the smallest magazine size of all the shotguns and one of the slowest reloads, however the weapon reloads all shells at once through a box magazine rather that reloading shells individually. The USAS 12 has the second highest range of any of the shotguns (only beaten by the Model 1887), but has very low damage at the edge of its range. Damage or Range is highly recommended, as with all shotguns. At medium range with the Damage proficiency, most kills will take one or two shots.
One unique hidden feature of the USAS 12 is that it increases sprint time by 75% (like the MP9 and Skorpion) when equipped on all platforms, similar to the effects of Extreme Conditioning. This effect can be combined with the Extreme Conditioning perk to allow the player to sprint 3.5x longer.
On January 25, 2012, the USAS 12 and KSG 12 were given a buff. The USAS 12 now shoots 9 pellets by default (like the KSG 12), as opposed to the default 6. This essentially gives it a 50% damage increase and a more reliable sense of shots to kill, due to the additional pellets.
- Grip - Unlocked at weapon level 2.
- Silencer - Unlocked at weapon level 5.
- Red Dot Sight - Unlocked at weapon level 12.
- Holographic Sight - Unlocked at weapon level 17.
- Extended Mags - Unlocked at weapon level 26.
- Kick - Unlocked at weapon level 4.
- Focus - Unlocked at weapon level 9.
- Attachments - Unlocked at weapon level 14.
- Melee - Unlocked at weapon level 19.
- Range - Unlocked at weapon level 23.
- Damage - Unlocked at weapon level 28.
- The Marksman III challenge is oddly achieved upon 300 kills with this weapon as opposed to the usual 75. The Marksman IV challenge is also unusual as it is achieved at 1000 kills.
- Despite the Elite description claiming that it has the highest damage in the shotgun class, the Create-a-class information says that the KSG 12 and Model 1887 have higher damage. When considering the close-range damage, USAS 12 is in the middle, being more powerful than the AA-12 and Striker, but weaker than the SPAS 12, Model 1887, and KSG 12. At long range, the USAS 12's damage is the second lowest, being only slightly higher than that of the AA 12.
- During the reload animation, the player accidentally hits the magazine on the side of the magazine slot before getting it in.