The M4A1 is based on the original AR-15 which was designed by Eugene Stoner and made by ArmaLite. It is a family of firearms and originates back to the M16.
— Item Description
The M4A1 is an Assault Rifle. It is the default weapon for the Rifleman class.
The M4A1 is the starter's gun for the Rifleman class and as such offers poor performance in comparison to assault rifles unlocked later in the game. Low damage, range and a poor rate of fire make it inadequate against armored enemies. However, a very controllable recoil pattern and high accuracy enable it to hit headshots with relative ease, allowing it to compete against more advanced weapons in medium-range combat.