Sig Sauer MCX-Spear LT Complete Upper Receiver 300 Blk 9″ UAMCX-300B-9B-LT-BLK

Sig MCX-Spear LT Complete Upper Receiver 300Blk 9″ UAMCX-300B-9B-LT-BLK Details

The MCX SPEAR LT developed for the SF community is the most advanced platform of its kind. Convert any M4/AR15 platform into a modernized folding firearm with superior reliability, durability, and accuracy.

Features:

• Adapts with any M4/AR15 Spec Lower Assembly
• Dual Rod Recoil Assembly Eliminates Buffer System
• M4 Adapter allows for Picatinny Rail Folding Stock Capabilities
• Adjustable Gas System for Suppressor Optimization
• Quick Change Barrel Design allows to easily swap calibers and barrel lengths
• Gas Piston Design Reduces Part Exposure to Carbon Fouling
• Designed to go 20k rounds before any maintenance part replacements
• SLX/SLH Next Gen Suppressor Designed QD Flash Hider for Clutch-Lok Adaptability
• Ambidextrous Charging Handle with Gas Deflector
• Replaceable parts (Cam Path Follower, Feed Ramp, Forward Assist/Deflector, Charging Handle Locking Pins) allow for longer receiver life over standard AR designs.
• Tapered Bolt Design Functions More Reliably and Lasts Longer than standard Square Lug M4 Bolt Designs.
• Nitride Coated Cold Hammer Forged Barrel for optimal accuracy and barrel life

Included items:

• Complete 9″ 300BLK upper assembly includes our removable 3-prong flash-hider ready to accept our SLH & SLX suppressor systems.
• Receiver extension delete stock adapter so you may mount any folding or static stock or brace that uses a vertical 1913 rail system.

Specifications

The Sig MCX-Spear LT Complete Upper Receiver 300BLK 9″ UAMCX-300B-9B-LT-BLK is a factory-built, premium rifle upper engineered for shooters who demand rugged reliability, modular adaptability, and proven performance right out of the box. Chambered in the versatile .300 Blackout cartridge with a compact 9-inch barrel, this complete upper is optimized for close-quarters effectiveness, suppressed shooting, and dynamic tactical applications.

Built on SIG Sauer’s SPEAR LT (Lightweight Tactical) platform, the upper features a robust piston-driven operating system that provides cleaner cycling and enhanced reliability compared to traditional direct impingement designs. This makes the MCX-Spear LT a standout choice for shooters who want consistent performance with supersonic and subsonic loads—especially when running suppressors or shooting in demanding environments.

The 9″ barrel offers a compact profile ideal for maneuverability in tight spaces while still maintaining excellent terminal performance for a short-barrel configuration. With .300 Blackout’s ability to use heavier subsonic ammo, this upper is well suited for suppressed setups where reduced noise and recoil control are priorities.

Finished in a sleek black coating, the upper delivers modern tactical aesthetics and increased corrosion resistance for long-term durability. The complete upper assembly comes ready to install on any compatible MCX or AR platform lower, with integral mounting surfaces and precise factory fitment that ensures reliable alignment and function.

Featuring SIG’s lightweight handguard and ample rail space, shooters can easily accessorize with optics, iron sights, lights, lasers, and other attachments to tailor the rifle to their mission profile. Whether used for defense, duty, hunting, or precision shooting, the Sig MCX-Spear LT Complete Upper Receiver 300BLK 9″ UAMCX-300B-9B-LT-BLK delivers dependable performance, tactical versatility, and premium build quality in a complete, ready-to-install package.