The M-170 Hammer Combat Shotgun first appears in the level: The Last Stand. It is very powerful and can kill a human mutant with direct hits from as few as two shells. Under normal conditions, it fires a single shell per shot and is semi-automatic, but the Hammer's alternate firing method launches two shells at once, which requires handlign it as a [[Wikipedia:Pump-action shotgun|Pump-action Shotgun]. It appears to be similar to a SPAS-12 in design and function, and thus it is likely based off of it. The M-170 normally appears to use gas-operated reloading, but when using it's alternate fire is pump-action. The reasoning for this is unclear.
The Hammer can be dual wielded, this is highly desirable because when firing both guns at once, it only takes one shot to kill a mutant. Thus, it is highly recommended that shotguns are duel wielded as they are highly efficient.
The Hammer is noticeably wide and is a distinct black in color. Like the SPAS-12, it features a folding stock. The M-170 is also double-barrel.
In the third level of the game, there are two key cards that you can collect. Once you have both, you can use them to open a door that leads to a small hallway that contains a databank and the first M-170 Shotgun you can get in the game.
This is risky, however, as the mutants will appear directly below you and jump through the hallway windows. It is recommended to keep your guns ready if you go to collect this Shotgun to avoid being caught off guard by the enemies that spawn there.