Sig MCX-Spear LT FDE Complete Upper 300Blk UAMCX-300B-9B-LT-IR 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.
Sig MCX-Spear LT FDE Complete Upper 300Blk UAMCX-300B-9B-LT-IR Specifications
| SKU | UAMCX-300B-9B-LT-IR |
|---|---|
| Model | SIG MCX-SPEAR LT |
| Barrel Extension | MCX |
| Barrel Length | 9 in [228.6 mm] |
| Barrel Profile | Medium |
| Barrel Rifling Type | Hammer Forged |
| Bolt Carrier Finish | DLC |
| Bolt Carrier Group Included | Yes |
| Caliber | 300BLK |
| Chrome Lined Barrel | No |
| Charging Handle Included | Yes |
| Color | Flat Dark Earth (FDE) |
| Forward Assist | Yes |
| Free Floated Handguard | Yes |
| Handguard Length (in.) | 7.94 |
| Handguard Inside Diameter | 1.48-in |
| Handguard Material | Aluminum |
| Muzzle Device | 3-Prong/SIG Suppressor QD |
| Muzzle Thread Pitch | 5/8-24 |
| Operating System | Gas Piston |
| Overall Length | 17.5-in |
| Weight | 3lb, 14.7oz |
| Receiver Finish | Black Anodized |
| Twist Rate | 1:5 |
The Sig MCX-Spear LT FDE Complete Upper 300BLK UAMCX-300B-9B-LT-IR is a premium factory-built upper receiver assembly engineered for shooters who demand top-tier reliability, modularity, and performance from the SIG MCX platform. Designed around the proven SPEAR LT system, this complete upper delivers exceptional durability and handling while chambered in the hard-hitting and versatile .300 Blackout, making it an outstanding choice for tactical use, suppressed shooting, and compact rifle builds.
Finished in a rugged Flat Dark Earth (FDE) coating, this upper not only matches modern tactical aesthetics but also provides added protection against wear and harsh environmental conditions. The SPEAR LT design is built around SIG’s advanced piston-driven operating system, offering cleaner operation and improved reliability compared to traditional direct impingement platforms—especially in high round count or suppressed configurations.
Chambered in 300BLK, the MCX-Spear LT upper is optimized for short-barrel performance, offering excellent energy delivery and flexibility with both supersonic and subsonic ammunition. This makes it a popular choice for shooters running suppressors who want reduced sound signature while maintaining strong terminal performance. The factory barrel and gas system are engineered for consistent cycling and dependable function across a wide range of loads.
The complete upper assembly includes SIG’s lightweight handguard design, offering plenty of rail space for optics, lights, lasers, and accessories. Built with SIG Sauer’s high-quality manufacturing standards, this upper provides excellent fitment, precise machining, and dependable performance straight out of the box.
Whether you’re upgrading an existing MCX lower, building a premium suppressed setup, or looking for a factory-correct SPEAR LT configuration, the Sig MCX-Spear LT FDE Complete Upper 300BLK UAMCX-300B-9B-LT-IR delivers elite performance, proven reliability, and modern modular capability in one complete package.
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