The MMR Tactical is chambered in 5.56 NATO (.223 Rem.), and operates via a direct-impingement gas system. The 16.25-inch, free-floating barrel is button rifled, with a 1 in 9 twist. It has a formidable-looking aluminum picatinny quad-rail forend, vented for quick cooling, and an A2-style muzzle brake. The rifle I had came with a six-position adjustable butt stock, though it can also be had with a fixed-position stock. It does have a dust cover, though no forward assist.