Description
The compact AR has always traded terminal performance for maneuverability. This barrel changes the trade: a heavier, higher-BC six-millimeter projectile from the same close-quarters frame, on the unmodified mil-spec .378 (5.56) bolt face and with no proprietary feed hardware. 6mm Max® is pressure-tested to SAAMI standards of 55,000 psi at EMRTC with published load data, Nosler brass and a BC Precision Ballistics factory-loaded 105 gr BTHP behind it.
Cut on the 6mm Max® SAAMI reamer in a 1:8 RH twist chosen to stabilize the heavy end of the menu, with feed ramps tuned beyond M4 specification for long, heavy projectiles — which on a 2.30″ overall length is the difference between a round that presents cleanly and one that hangs on the ramp.
The low-profile gas block is installed and pinned before shipment — port alignment verified, set screws torqued to specification, and a stainless steel coiled pin through block and barrel. Short barrels in this class run pinned fixed gas at Second of Ten; adjustable blocks belong on the longer precision barrels. The carbine-length gas is tuned to the VLTOR A5 receiver extension and buffer system, and is intended for an A5-equipped lower.
Converted to the LMT® MRP™ barrel interface, then inspected, gauged and assembled by the Second of Ten build team to a documented standard. Installs with the MRP™ upper’s factory barrel hardware — no proprietary tooling and no permanent modification to the receiver. Headspace is gauged and recorded on the barrel inspection record before shipment.
Ships shooter ready: gas tube installed and the muzzle protected by the SOT Standard Barrel Thread Protector (CNC-machined steel, black or nitride finish), with no muzzle device fitted. Brakes, flash hiders and suppressor mounts are fitted and timed to order through the SOT Custom Shop. A headspaced bolt carrier group can be added and gauged to this barrel: SOT Enhanced Microbest C158 MPI DLC+, SOT Enhanced HM Defense in Black Nitride, or the SOT Enhanced Microbest Super-Stake with the Young Manufacturing HMB™ bolt.
Includes
- 10.5″ Mos-Tek barrel, converted to the LMT® MRP™ interface
- Low-profile gas block, black nitride finish, installed, aligned, torqued and pinned
- Gas tube sized to the gas system, stainless steel, installed
- SOT Standard Barrel Thread Protector, fitted (CNC-machined steel, black or nitride finish)
- Vacuum-sealed, with a Zerust® corrosion-inhibitor tube in the bore (remove before firing)
- Barrel inspection record (SOT-BIR-001)
Options
- Headspaced bolt group: SOT Enhanced Microbest C158 MPI DLC+
- Headspaced bolt group: SOT Enhanced HM Defense, Black Nitride
- Headspaced bolt group: SOT Enhanced Microbest Super-Stake with Young Manufacturing HMB™
- Muzzle devices from other manufacturers, installed and timed — for a specific muzzle device, please ask before ordering
Matching headspaced bolt
Choose a bolt above and we gauge headspace with it in this barrel and record the pairing on the barrel inspection record, so the two ship as a matched set.
Full specifications, photos and the inspection standard
Shipping: we do not ship barrel assemblies to CA, CT, DE, DC, HI, IL, MD, MA, NJ, NY, RI or WA, or to Denver, CO or Cook County/Chicago, IL. Questions? Ask your local FFL.
WARNING: This product can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.
