I opened up ArmA 3 following the latest Dev Update (on 11/30/2013, US Standard Calendar). This is not tested in the updates to come out within a week before that date.
For whatever reason, all of the primary infantry weapons (MX rifles, Mk18, Katiba Family, and the F2000s... whatever their in-game name is) all do about as much damage as the 9mm pistols. For test purposes, I've fired a Mk18 (7.62 mind you) into a teammate's face at point blank; took 4 rounds to kill him. When this first happened, I assumed working helmets were finally added to the game; I spawned in a civilian (no helmet) and had the same results with the Mk18.