The M4A1 is described in the game as:

A full-auto assault rifle, used by U.S. spec ops.

It can be found in central Flor de Oro province, at a house in the middle of nowhere. There are six Unidad soldiers around the house. The weapons case is outside, against the north wall of the house.

My approach here wasn’t subtle at all. I came up the road to the east and killed the first soldier out the front of the house, but the body was spotted and we went loud and reinforcements were called in… it wasn’t pretty. I reckon you could sneak up and take the weapon without being seen – especially at night – because most of the soldiers are on the back side of the house to the west, and the northern side is against a hill with some rocks.

The M4A1 is a great little gun, with a high rate of fire beaten only by the G2 FAMAS (found in Inca Camina). It’ll accept pretty much all AR weapon accessories on its platform, but the tall front iron sight does slightly obscure many of the scopes.

For its rate of fire, the recoil is predictable and manageable. It does go through ammo quickly of course, but there are semi-auto and three round burst fire options available. The standard 20 round magazine can be boosted 50% to 30 rounds with the extended mag which you can pick up in Mojocoyo and further still with the 50 round large magazine found in Libertad which is definitely worth picking up in my book.