Home / Parts / Barrels / LMT® MRP™ Barrels / Ballistic Advantage 18″ 6mm ARC with RIFLESPEED
// 6mm ARC · LMT® MRP™ compatible barrel
Ballistic Advantage 18″ 6mm ARC with RIFLESPEED
18″ Ballistic Advantage Premium Black Series barrel in 6mm ARC, converted for LMT® MRP™ upper receivers, with the RIFLESPEED Gas Control installed and pinned. #887 plunger fitted, #917 included.
In stock · ships shooter ready
Price on request
- SKU BBL-6ARC-B180RS-MRP
- Caliber 6mm ARC
- Barrel length 18″
- Gas Rifle-length
- Muzzle Thread protector
Ordered through the SOT Custom Shop — tell us your MRP™ upper and rail length and we’ll confirm fit before it ships.
// Specifications
The numbers
| Specification | Value |
|---|---|
| SOT SKU | BBL-6ARC-B180RS-MRP |
| Barrel maker | Ballistic Advantage |
| Caliber | 6mm ARC |
| Barrel length | 18″ |
| Material | Hardened 416R stainless |
| Profile | SPR — Mk12 Mod H, extended .750″ section |
| Twist rate | 1:7 |
| Bore | Unlined stainless |
| Finish | QPQ black, corrosion resistant |
| Gas system | Rifle-length, straight tube |
| Gas block | RIFLESPEED Gas Control, 12 settings; installed and pinned; #887 plunger fitted, optimized for 6mm ARC; #917 included |
| Gas journal | .750″ |
| Barrel extension / feed ramps | Nickel boron coated extended M4 feed ramp extension |
| Barrel interface | LMT® MRP™ upper receivers |
| Muzzle threads | 5/8×24 |
| Thread protector | SOT Standard Barrel Thread Protector, fitted — CNC-machined steel, black or nitride finish |
| Muzzle device | None — fitted and timed to order |
| Bolt face | 6.5 Grendel / 6mm ARC (Type II bolt required) |
| Magazines | 6mm ARC magazines required |
| Weight | 41.3 oz |
| Inspection | Headspace gauged; bore and crown inspected; recorded on SOT-BIR-001; plunger and setting recorded |
| Availability | In stock |
| Price | On request |
// About this barrel
Built, converted, gauged.
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
What ships
- 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
Add to the build
- 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
Every headspaced bolt group is gauged against this barrel and recorded with it.
// Matching headspaced bolt
Add a bolt, headspaced to this barrel
Any of these 6mm ARC bolt face bolts can be added to this barrel. We gauge headspace with the bolt in this barrel and record the pairing on the barrel inspection record, so the two ship as a matched set.
| Bolt | Details | Price |
|---|---|---|
| Young Manufacturing 6mm ARC HMB™ bolt, black nitride | Item 1-50-12-306 | $99.95 |
| Young Manufacturing 6mm ARC HMB™ bolt, chrome | Item 1-50-12-307 · check availability | $149.95 |
Want a complete bolt carrier group instead? See the headspaced bolt groups under Options above, or ask the Custom Shop.
// Before you order
Fits LMT® MRP™ upper receivers only. Cut for LMT® MRP™-pattern upper receivers only — it will not fit a barrel-nut upper. Rail length governs clearance; tell us your receiver and rail and we will confirm fit before it ships.
16″ or longer. Not a short barrel under federal law, so short-barreled-rifle rules do not come into it. The firearm’s overall configuration is the purchaser’s responsibility.
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.
Shipping. We do not ship barrel assemblies to California, Connecticut, Delaware, the District of Columbia, Hawaii, Illinois, Maryland, Massachusetts, New Jersey, New York, Rhode Island or Washington, or to Denver, Colorado, or Cook County/Chicago, Illinois. If you have questions, consult your local FFL.
Warranty. We warrant the conversion and the fit. A converted barrel is modified from its original configuration, so any coverage from the original manufacturer is at their discretion. If something goes wrong, come to us first.
// The rest of the range
Other LMT® MRP™ barrels
Monobloc® is a registered trademark of HM Defense. HMB™ is a mark of HM Defense, LLC, used under license. 6mm Max® is a registered trademark of BC Precision Ballistics. 6mm ARC is a trademark of Hornady Manufacturing Company. LMT® and MRP™ are marks of Lewis Machine & Tool Company. RIFLESPEED, SOLGW, Ballistic Advantage and Mos-Tek are marks of their owners. Second of Ten LLC is not affiliated with, sponsored by or endorsed by any company named here.