LMT Monolithic 5.56 NATO 12.5in Mid-Length Barrel

The LMT Monolithic 5.56×45 NATO 12.5-inch Mid-Length Barrel is a bare replacement barrel from LMT Defense (brand part no. R-L7MJ1B) built for LMT’s Monolithic Rail Platform (MRP) upper receivers. It is chambered in 5.56 NATO with a 1-in-7 twist rate suited to a wide range of bullet weights, and its mid-length gas system spreads dwell time more evenly across the cycle than a carbine-length system on the same barrel length. Finished in black, it is sold as a barrel only, with no upper receiver, bolt, or lower included.

Key Specifications

• It measures 12.5 inches, a common AR-15 carbine barrel length.
• It is chambered in 5.56×45 NATO.
• It uses a 1-in-7 twist rate, suited to a wide range of 5.56/.223 bullet weights.
• It runs a mid-length gas system, spreading dwell time more evenly than a carbine-length system at this barrel length.
• It is built for LMT’s Monolithic Rail Platform (MRP) upper receivers.
• It is finished in black.

Frequently Asked Questions

Does this barrel make my AR-15 an SBR? No. A barrel sold on its own is not a regulated firearm. Installing this barrel on a complete, already-assembled rifle lower with a shoulder stock requires an approved ATF Form 1 before assembly; building it as a pistol with no stock avoids that requirement entirely.

What upper does this barrel fit? It is built for LMT’s Monolithic Rail Platform (MRP) upper receivers.

Does this include a bolt or upper receiver? No, this is a bare barrel only; the upper receiver, bolt carrier group, and lower are sold separately.

Buy the LMT Monolithic 5.56 NATO 12.5in Mid-Length Barrel

Order the LMT Monolithic 5.56 NATO 12.5in Mid-Length Barrel through our AR barrels selection at Schaefer Defense and we will ship it fast, fully insured, from our Lubbock, TX gun shop.