There are nearly as many different ammunition types as there are guns in DayZ.
Just as the guns inside the game are designed after real-life weapons, so are the ammunition cartriges, shells, bolts and grenades.
Players can Convert Magazines of some types of ammunition
With the 126.96.36.199 update, most ammunition can be seen on the ground, unlike before when most ammunition came in small green bags. This change has some bugs; for instance, some shotgun shells appear as pistol ammo when on the ground.