Home / Parts / Barrels / LMT® MRP™ Barrels / SOLGW Precision SPR 18″ 6mm Max® with RIFLESPEED
// 6mm Max® · LMT® MRP™ compatible barrel
SOLGW Precision SPR 18″ 6mm Max® with RIFLESPEED
18″ SOLGW Precision SPR barrel in 6mm Max® with the RIFLESPEED Gas Control installed and pinned. Twelve numbered gas settings, #887 plunger fitted and #917 included.
In stock · ships shooter ready
Price on request
- SKU BBL-6MAX-B180RS-MRP
- Caliber 6mm Max®
- 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-6MAX-B180RS-MRP |
| Barrel maker | SOLGW |
| Caliber | 6mm Max® |
| Barrel length | 18″ |
| Material | 416R stainless |
| Profile | SPR |
| Twist rate | 1:7.5 |
| Rifling | SOLGW P3 polygonal, 3-groove |
| Bore | Unlined stainless |
| Finish | Black oxide |
| Gas system | Rifle-length, straight tube |
| Gas block | RIFLESPEED Gas Control, 12 settings; installed and pinned with a stainless steel coiled spring pin; #887 plunger fitted, optimized for 6mm Max®; #917 included |
| Gas journal | .750″ |
| Barrel interface | LMT® MRP™ upper receivers |
| Muzzle threads | 5/8×24 |
| Thread protector | SOT Standard Barrel Thread Protector, fitted — CNC-machined steel, nitride finish |
| Muzzle device | None — fitted and timed to order |
| Bolt face | Standard 5.56 (.378) |
| Magazines | 6mm Max® magazines required |
| 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.
The same 18″ SOLGW Precision SPR barrel, with the RIFLESPEED Gas Control fitted in place of the fixed block — same .750″ journal, same alignment check, same stainless coiled pin, twelve numbered settings instead of one.
Fixed gas ports are sized for the worst case, which means nearly every AR leaves the factory overgassed by design. An adjustable block takes that back — but the real value is repeatability. Twelve numbered positions with a tactile click, adjusted by hand without tools and without pulling the handguard, give you a setting you can record beside the load and the conditions and return to a year later. This is a cycling and impulse feature, not an accuracy feature, and it cannot add gas beyond what the barrel port gives it.
Fitted and tuned with the #887 plunger — the size RIFLESPEED recommends for the six-millimeter cartridges. A shorter plunger meters more gas at every position, so the working setting sits low on the dial with reserve held above it. RIFLESPEED’s standard #917 plunger is also included in the box, so the gas system can be configured further by the shooter: fit the #917 and the whole range moves up the dial. The plunger and setting are recorded on the barrel inspection record.
An adjustable block is the one component you deliberately reach out and turn, so it gets both retention methods: set screws torqued to specification and a stainless steel coiled pin through the control body and the barrel. A recorded gas setting is worthless if the block can creep underneath the numbers.
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.
At 18 inches this barrel builds a conventional rifle — no tax stamp, no registration and no wait. Requires 6mm Max® magazines.
// Includes
What ships
- 18″ SOLGW Precision SPR barrel, converted to the LMT® MRP™ interface
- RIFLESPEED Gas Control, installed, aligned, torqued and pinned with a stainless steel coiled spring pin
- #887 plunger installed and tuned, optimized for 6mm Max®
- #917 plunger, loose in the box
- RIFLESPEED straight rifle-length gas tube, installed
- SOT Standard Barrel Thread Protector, fitted (CNC-machined steel, 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: 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
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 5.56 NATO / 6mm Max® 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 |
|---|---|---|
| Microbest C158 MPI bolt kit, chrome (phosphate extractor) | Bolt, extractor, firing pin, retaining pin and cam pin | $79.00 |
| HM Defense HMB™ bolt, black nitride | Cam pin socket in place of a through-hole | $135.00 |
| Young Manufacturing 5.56 M-16 bolt, black nitride | Item 1-50-12-301 | $89.95 |
| Young Manufacturing 5.56 M-16 bolt, chrome | Item 1-50-12-303 | $129.95 |
| Young Manufacturing 5.56 HMB™ bolt with cam pin, black nitride | Item 1-50-12-302 | $99.95 |
| Young Manufacturing 5.56 HMB™ bolt with cam pin, chrome | Item 1-50-12-300 | $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.