As you would expect, the ARX100 is semi-automatic and has a 16 inch barrel with a true 5.56mm NATO chamber. The muzzle device is a NATO-style flash hider/muzzle brake. By using a great deal of high-strength polymer and aluminum, as well as steel where needed, Beretta was able to keep the empty weight relatively low at only 6.8 pounds. For a full-sized rifle this is exceptional. By comparison, the empty weight for the Colt M16A2 is 7.5 pounds.
The operation for this rifle is a short-stroke, gas piston. One of the features that the Beretta engineers built into the rifle was “the lightweight technopolymer receiver allows for reliable operation with virtually no lubricants.” The old Marine in me cringes at the thought of running a dry rifle, but I appreciate the idea of deliberately minimizing metal and metal contact to reduce friction.
All of the manual controls on the ARX100 are built to be ambidextrous. I suppose the only feature that is not “ambi” is the side folding stock which both retracts and folds to the right side of the receiver. The charging handle for the bolt can be set up so that it is accessed either from the left side of the receiver or the right. As you might expect, Italy, being a NATO member, required the ARX160 to use the STANAG 5.56mm aluminum magazine. The ARX100 followed suit. The magazine release is ambidextrous.