The LMT MRP-L Quad 5.56/300 BLK 9.25” Assembled Upper Receiver (LMT part no. L7S1A) is a complete Mars-L monolithic upper built for shooters who want a short-barreled 5.56 NATO or .300 AAC Blackout pistol or SBR upper without sourcing individual parts. The monolithic rail design ties the handguard directly into the upper receiver, eliminating the barrel nut interface and giving a rock-solid, free-float platform for optics and accessories. At 9.25 inches, this upper suits compact pistol builds where maneuverability matters more than long-range reach. LMT assembles these uppers to the same standard used on its SOPMOD and MARS-L contract rifles.

Key Specifications

• Measures 9.25 inches, sized for short-barrel pistol and SBR-length AR15 builds.
• Chambered for 5.56 NATO or .300 AAC Blackout, giving flexibility on barrel choice.
• Built on the Mars-L monolithic rail platform, integrating the handguard directly into the upper receiver.
• Sold fully assembled, ready to drop onto a compatible AR15 lower.
• Uses a full quad Picatinny rail, giving mounting options around the full handguard.
• Eliminates the barrel nut interface entirely, helping the upper hold zero on mounted optics.
• Compatible with mil-spec AR15 lower receivers accepting a standard pivot and takedown pin.

Frequently Asked Questions

What does the term monolithic mean on this upper? The handguard and upper receiver are machined as one continuous rail section instead of clamping a separate handguard to a barrel nut, improving rigidity for optics.

Does this upper come with a bolt carrier group? It is sold as an assembled upper receiver; confirm current listing contents before pairing with a BCG and charging handle.

Buy the LMT MRP-L Quad 5.56/300 BLK 9.25-inch Assembled Upper Receiver

Shop the LMT Defense MRP-L upper in our AR15 uppers selection, with fast, insured shipping from our Lubbock, Texas gun shop.