(standard) 14 in.
Developed exclusively for U.S. special operations forces and the demanding environments they operate in, the Mk16 Special Operations Forces Combat Assault Rifle is a gas-piston operated 5.56 carbine that features a modular design to allow the operator to configure the rifle for specific missions.
The SCAR has two receivers: The lower is constructed of polymer, and the upper receiver is one piece and constructed of aluminum. The SCAR features an integral, uninterrupted Picatinny rail on the top of the aluminium receiver, two removable side rails and a bottom one that can mount any MIL-STD-1913 compliant accessories.
It has a polymer lower receiver with an M16 compatible pistol grip, flared magazine well, and raised area around magazine and bolt release buttons. The front sight flips down for unobstructed use of optics and accessories. The rifle uses a 'tappet' type of closed gas system much like the M1 Carbine while the bolt carrier otherwise resembles the Stoner 63 or Heckler & Koch G36.
In June 2011, SOCOM announced it would not purchase the Mk16 to field to special operations forces. Later that year, Naval Special Warfare issued a solicitation to purchase the Mk16 over a five year period.