Description
The SIG Sauer MCX-SPEAR LT IR 300 BLK 9″ SBR is a compact, integrally suppressed upper receiver group designed for shooters who need a short, quiet, and reliable platform in .300 Blackout. Its key benefit is factory-level suppression without the hassle of a tax stamp or extra length — you get a 9-inch barrel with an integrated reflex suppressor that keeps the overall package short and handy. We’ve had these on our shelves since fall 2025, and the return rate is low; customers generally get exactly what they expect from this product. Staff note: this upper has a slightly tighter fit on Gen4 frames compared to Gen5 — not an issue, just noticeable.
Key Highlights
- Integral reflex suppressor — no NFA wait, no extra stamp, just a short, quiet package.
- 9-inch chrome-moly vanadium barrel with a 1:5 twist rate, optimized for heavy subsonic .300 BLK loads.
- Handguard features M-Lok slots at 3, 6, and 9 o’clock for accessories; full-length Picatinny top rail.
- Adjustable gas piston system — run suppressed or unsuppressed with reliable cycling.
- Comes with a SIG Sauer MCX lower adapter to fit standard AR-15 lowers (Gen4 or Gen5).
Product Details
| Caliber | .300 Blackout |
| Barrel Length | 9 inches |
| Twist Rate | 1:5 |
| Overall Length | 16.2 inches (with suppressor) |
| Weight (measured) | 4.2 oz |
| Suppressor | Integral reflex, 1.5-inch diameter |
| Handguard | M-Lok aluminum, 7.5-inch |
| Gas System | Adjustable, short-stroke piston |
What Buyers Ask
Does this upper require a tax stamp?
No. The MCX-SPEAR LT IR 300 BLK 9″ SBR is an upper receiver group with an integral suppressor. The suppressor is permanently attached, making the barrel length 16.2 inches overall — no NFA stamp needed. You can mount it on any standard AR-15 lower.
Will this fit my existing AR-15 lower?
Yes, it comes with a SIG MCX lower adapter. It fits both Gen4 and Gen5 lowers. Staff note: fit is slightly tighter on Gen4 frames — it’s not a problem, just a snugger feel during installation.
What ammunition works best with the 1:5 twist?
The 1:5 twist is designed for heavy subsonic loads (200-220 grain). It stabilizes these bullets well and helps with consistent expansion. It also works with supersonic ammo, but you’ll get the best accuracy and noise reduction with subsonic rounds.
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