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Sig Sauer MCX SPEAR LT 9" Barrel & Gas Block Assembly – .300 BLK – 8901315
The Sig Sauer MCX SPEAR LT 9-Inch Barrel Assembly (8901315) is a factory-original caliber exchange kit designed to provide the ultimate suppressed performance for the MCX SPEAR LT platform. In 2026, the 9-inch .300 Blackout configuration remains the "gold standard" for the MCX, offering the perfect dwell time to reliably cycle both subsonic and supersonic ammunition. This assembly features a 1:5 twist rate, which is specifically engineered to stabilize heavy, high-BC subsonic projectiles (like 220gr OTM) even out of a short barrel, ensuring maximum accuracy and terminal performance.
Built from high-grade stainless steel with a durable black finish, this complete assembly includes the barrel, a pre-installed two-position adjustable gas block, and the piston valve assembly. The adjustable gas system allows the user to quickly tune the rifle for suppressed or unsuppressed use, minimizing blowback and reducing wear on internal components. It comes equipped with Sig’s tapered lug design and is threaded 5/8x24 TPI, topped with a Rocksett® SIG QD suppressor-ready flash hider. Whether you are converting a 5.56 NATO SPEAR LT for home defense or replacing a high-round-count barrel, the 8901315 provides the unshakeable OEM reliability required for the MCX's short-stroke piston system.
Includes: (1) Complete 9" .300BLK Barrel, (1) Adjustable Gas Block Assembly, (1) Piston/Valve Assembly, and (1) SIG QD Flash Hider.
Key Features
- SPEAR LT Optimized: Features the lightened profile and updated geometry of the Gen 3 MCX SPEAR LT, reducing front-end weight compared to older Virtus barrels.
- Ultra-Fast 1:5 Twist: Optimized for .300 Blackout, ensuring heavy subsonic rounds are fully stabilized for pinpoint accuracy and suppressor safety (no baffle strikes).
- Adjustable Gas System: Two-position valve allows for "Normal" and "Adverse/Suppressed" settings to ensure 100% cycling reliability with any load.
- Stainless Steel Construction: Offers superior corrosion resistance and longevity, especially when subjected to the high heat of rapid suppressed fire.
- Tapered Bolt Compatibility: Designed for use with the Sig Sauer tapered lug bolt, providing a more secure lockup and improved secondary extraction.
- Direct Swap Versatility: Can be swapped into any MCX SPEAR LT upper receiver in minutes using the standard two-bolt retention system.
Product Specifications
- Brand: Sig Sauer
- Model: MCX SPEAR LT Barrel & Gas Block Assembly
- Caliber: .300 AAC Blackout
- Barrel Length: 9.0 Inches
- Twist Rate: 1:5
- Thread Pitch: 5/8x24 TPI
- Material: Stainless Steel
- Finish: Black Nitride
- Operating System: Short-Stroke Gas Piston
- Weight: 2.13 lbs (Complete Assembly)
- MPN: 8901315
- UPC: 798681675258
