The Calico E50 is the standard issue machine pistol of the Mars Police. Holds 50 rounds. Can fire in semi-auto and 3-round burst modes. It appears to be based on the Calico M950 pistol.
The Beretta R2 is used by Mars Police and other enemies on Mars. It can be obtained after traveling to Mars. In MP, it replaces the PM12S. It is a futurized version of the Beretta PM12S, and unlike that one, the R2 holds a correct 32 rounds.
Winchester DB Auto
The Winchester DB Auto is magazine-fed double barrel shotgun. Holds 16 shells. The secondary attack fires both barrel at the same time.
The Taff 20-4 is a select-fire, magazine-fed grenade launcher, that can fire in either semi-auto or 4-round burst modes. The magazine capacity is 20 rounds. It can be found only on Mars. The weapon looks like a futuristic, 6-barreled version of the Norinco QLZ-06, fitted with a G36-type carrying handle / sight.
Based on the break-action M79 grenade launcher, the GDL M60 can fire timed or impact grenades.
These 3-barreled drone guns can be seen during a boss battle on Earth, and later in the prison on Mars. They look like futurized M197 Vulcans.