Sig Sauer MCX-Spear LT Complete Upper Receiver 556 Blk 11.5″ UAMCX-556N-11B-LT-BK

Sig MCX-Spear LT Complete Upper Receiver 556 Blk 11.5″ UAMCX-556N-11B-LT-BK 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 Pic 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 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 11.5″ 5.56 NATO 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.

Thread pitch 1/2×28

Specifications

The Sig MCX-Spear LT Complete Upper Receiver 5.56 BLK 11.5″ UAMCX-556N-11B-LT-BK is a premium, ready-to-install upper receiver assembly built for shooters who demand reliability, modularity, and tactical performance from their SIG MCX platform. Chambered in the versatile 5.56 NATO caliber and paired with an 11.5-inch barrel, this upper offers a well-balanced combination of maneuverability and effective engagement range, making it ideal for duty use, tactical builds, training, and sport shooting.

Constructed on SIG’s proven SPEAR LT (Lightweight Tactical) platform, this complete upper features a robust piston-driven operating system that enhances reliability by reducing carbon buildup in the action—especially when shooting suppressed or in adverse conditions. The piston design delivers smoother cycling and greater consistency compared to direct-impingement systems, helping ensure dependable performance under heavy use or in harsh environments.

The 11.5″ profile strikes an excellent balance between compact handling and ballistic efficiency, providing quicker target transitions in close to intermediate ranges without sacrificing terminal performance. Whether you’re building a patrol rifle, home defense carbine, or precision-oriented setup, this length keeps the rifle agile while maintaining effective accuracy out past typical close-quarters distances.

Finished in a durable black coating, the upper receiver and handguard deliver corrosion resistance and rugged protection against wear. The complete upper includes factory-machined rail mounting surfaces that provide plenty of space for optics, aiming devices, lights, foregrips, and other mission-enhancing accessories. SIG’s precision fitment ensures proper alignment and secure interface with compatible MCX lower receivers for consistent function and reliability.

Whether used for professional applications, personal defense, or recreational shooting, the Sig MCX-Spear LT Complete Upper Receiver 5.56 BLK 11.5″ UAMCX-556N-11B-LT-BK delivers premium build quality, proven tactical performance, and the adaptability shooters expect from SIG Sauer’s MCX platform. Its combination of piston reliability, compact profile, and capability with a common service caliber rounds makes this upper a versatile core component of a defensive or duty rifle system.