The M249 is a machine gun that offers squad-level support. However, it also has a lot of recoil added to it as well so that the SMG is not made completely obsolete. In addition to decreasing accuracy, the longer the player fires the gun, the M249's recoil knocks the player back a bit as long as the fire key is held down.
The M249 can first be obtained by taking it from a dead ally in the chapter Friendly Fire. If not picked up there, it can be obtained at the beginning of the chapter Foxtrot Uniform.
Headshots will make quick work of even the strongest enemies, so one should try to aim for the head if possible.
Crouching will make the weapon more accurate, so one should be sure to crouch as often as possible when using it.
Ammo for this weapon is extremely rare until the end of the chapter Vicarious Reality.
The M249 has a fairly long reload time, so one should make sure to be safe before reloading.
Tapping the primary fire button instead of holding it will greatly reduce the recoil. Moving forward removes the recoil but decreases accuracy.
If sufficient ammunition is available, the M249 can be used to impede falls by shooting downwards while falling. The backwards recoil will constantly push towards the player's back, regardless of direction, resulting in lower downwards momentum.