M4 - 4 Versions RHS compatible

The M4 is the carbine version of the M16A2, which is the NATO-caliber variant of the M16. The M4 has a shorter barrel and an adjustable length stock. The M4 retains the direct impingement gas system of the M16. The action cycles due to gas siphoned from the barrel impinging via a small tube onto a piston which is part of the bolt. The M4 is a select-fire rifle. Most variants allow for full automatic fire, with some having a similar three round burst mechanism as the M16A2. Some M4 variants are fitted with an integrated carry handle that houses the rear sights. The vast majority of M4 models are of the flattop variant. These feature a Picatinny accessory rail on top of the receiver for mounting optical or mechanical sights.