Description
The HM Defense Monobloc® is machined from one piece of 4150 chrome-moly vanadium: barrel, gas journal and gas block together. There is no gas block to index, no set screws to back out, no taper pins to shear and no clamp interface to shift under heat. The gas port is drilled to a known size in a fixed location and it stays there.
Mid-length gas at 12.5″ — lower port pressure and a longer dwell than carbine gas, which shows up as a softer impulse and less wear through the bolt carrier group. Every length in this family runs mid-length, so the rifle keeps the same character when you change barrels. Bore is standard (unlined); finish is black Cerakote.
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 HM Defense in Black Nitride, or the SOT Enhanced Microbest Super-Stake with the Young Manufacturing HMB™ bolt.
Includes
- 12.5″ Monobloc® barrel, converted to the LMT® MRP™ interface
- Mid-length gas tube, black nitride finish, 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 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.
