The AKM is an effective close to medium range assault rifle which can be found in all military loot spawns. It is more powerful than any of the other AK variants, but is also much louder. It will kill a normal zombie with a single shot to the body, while "viral" zombies take several rounds to kill.
It is the only AK with zeroing capabilities, and can be zeroed up to 800m. By default, you can press Page Up and Page Down to adjust the zeroing on the AKM.