Description
Hardened 416R stainless in the SPR profile, QPQ black, corrosion resistant, 1:7 twist, with the Premium Black Series nickel boron coated extended M4 feed ramp extension. The profile is specifically Mk12 Mod H, with a longer .750″ dimension than a standard SPR contour. 6mm ARC gives you a high-BC six-millimeter projectile in an AR-15-sized receiver, and 18 inches on rifle-length gas is the configuration the cartridge was drawn for.
The RIFLESPEED Gas Control is installed and pinned before shipment — twelve numbered positions with a tactile click, adjusted by hand without tools and without pulling the handguard. The value is repeatability: a setting you can record beside the load and the conditions. Fitted and tuned with the #887 plunger, the size RIFLESPEED names for 6mm ARC, with the standard #917 plunger included so the gas system can be configured further by the shooter.
Set screws torqued to specification plus a stainless steel coiled pin through the control body and the barrel — the screws clamp the block onto the journal, the pin stops rotation independent of clamping force. Port alignment is verified before pinning. The plunger and setting are recorded on the barrel inspection record.
6mm ARC runs the 6.5 Grendel case head, not the 5.56 bolt face, so this barrel needs a Grendel-pattern bolt — the bolt changes, the carrier does not. Three matched bolt groups can be added and gauged to this barrel: an NP3-finished carrier with a Type II dual-ejector bolt; an NP3-finished carrier with the Young Manufacturing 6mm ARC Black Nitride HMB™; or the Microbest Super-Staked all-chrome carrier with the Young Manufacturing 6mm ARC Chrome HMB™. The NP3 carrier option includes an index-marked gas key and an arrow-marked cam pin.
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.
At 18 inches this barrel builds a conventional rifle — no tax stamp, no registration and no wait. Requires 6mm ARC magazines and a Grendel-pattern bolt.
Includes
- 18″ Ballistic Advantage Premium Black Series barrel, converted to the LMT® MRP™ interface
- RIFLESPEED Gas Control, installed, aligned, torqued and pinned
- #887 plunger installed and tuned, optimized for 6mm ARC
- #917 plunger, loose in the box
- RIFLESPEED straight rifle-length gas tube, 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: NP3 carrier with Type II dual-ejector bolt
- Headspaced bolt group: NP3 carrier with Young Manufacturing 6mm ARC Black Nitride HMB™
- Headspaced bolt group: Microbest Super-Stake with Young Manufacturing 6mm ARC Chrome 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.
