Geissele Super Duty MOD 1 5.56 NATO 13.9"Bbl Black Short Barrel Rifle (NFA) 08-521B

13.9 inches lands in an interesting spot - short enough to stay maneuverable, long enough to avoid some of the velocity loss that comes with going shorter still. The Geissele Super Duty MOD 1 5.56 NATO 13.9" 08-521B puts that length to work on top of every upgrade that defines the MOD1 series over the standard Super Duty lineup.

The barrel is precision machined and cold hammer forged from top-tier steel, finished in manganese phosphate with a chrome lining for genuine resistance to heat and corrosion over years of use. An HUXWRX Flash Hider-QD 556 caps the muzzle, suppressor-ready straight out of the box. As with the rest of this Geissele Super Duty SBR line, the real engineering shows up in Geissele's own Reliability Enhanced Bolt Carrier Group - Nanoweapon coated, with a properly staked and torqued gas key lined in chrome, plus an H13 tool steel cam pin carrying its own Nanoweapon coating for corrosion and wear resistance. The Stressproof Bolt is precision machined from Carpenter 158+ barstock, giving this Geissele 13.9 Super Duty build real strength and fatigue resistance that holds up shot after shot.

The two-stage SSA-E X Lightning Bow trigger delivers a smooth, light first-stage take-up followed by a crisp break, mounted in a Super Duty Lower machined from 7075-T6 aluminum with Geissele's Ultra Duty Lower Parts Kit and ambidextrous configurable safety. An updated MK16 Super Modular Rail mates tightly to the upper to eliminate rotation, leaving room for optics, red dots, or night vision devices. A B5 Systems Enhanced Sopmed Stock and Airborne Charging Handle round out the build.

Key Features

• Precision machined, cold hammer forged barrel with chrome lining
• HUXWRX Flash Hider-QD 556 suppressor-ready muzzle device
• Reliability Enhanced Bolt Carrier Group, Nanoweapon coated
• Stressproof Bolt machined from Carpenter 158+ barstock
• SSA-E X Lightning Bow two-stage trigger
• Super Duty Lower with Ultra Duty Lower Parts Kit
• Updated MK16 Super Modular Rail
• B5 Systems Enhanced Sopmed Stock and Airborne Charging Handle