SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB
SIG Sauer MCX SPEAR LT 9″ .300 Blackout Barrel & Gas Block Assembly, NIB
So you want the factory SIG 9-inch .300 BLK barrel for your MCX SPEAR LT build or caliber swap. This is it. The genuine SIG Sauer MCX SPEAR LT 9″ .300 Blackout barrel and gas block assembly, part number 8901315. Stainless steel. Complete gas block included. New in box.
SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB This is a factory SIG replacement barrel, not an aftermarket copy. First, it’s a genuine drop-in assembly for any MCX SPEAR LT already configured in .300 BLK. Next, the adjustable gas block lets you tune for suppressed or unsuppressed use without tools, critical for running subsonic .300 BLK through a suppressor. Finally, it ships with the complete gas block assembly installed, so you’re not sourcing gas components separately.
Is this SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB legal to install on any MCX lower?
Only on specific configurations — and SIG states this directly. So this barrel may only be installed on a lower receiver that either has no stock attached and is not recorded as a rifle by the manufacturer, or is registered with the BATFE as a short-barreled rifle. Therefore, you may NOT install this on a standard rifle-configured MCX lower without prior SBR registration. SIG America states this explicitly on the product page — all NFA rules apply.
What’s actually included with this SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB assembly?
The complete barrel and gas block assembly. So you get the 9″ stainless steel barrel with the gas block assembly pre-installed. Also, the barrel is threaded 5/8×24 for standard muzzle devices and suppressors. Therefore, you don’t need to source a separate gas block or gas system — everything mounts as a complete unit.
Why does the adjustable gas block matter specifically for .300 BLK?
Subsonic .300 BLK demands it. So subsonic loads generate significantly less gas pressure than supersonic loads. Also, without adjusting the gas block down when running a suppressor, you get excessive gas in the face and potential reliability issues on the lighter subsonic loads. Therefore, the adjustable gas block on this SPEAR LT assembly is a genuine operational feature, not just a marketing checkbox — especially if you’re running this suppressed.
Does this SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB fit any other MCX model besides the SPEAR LT?
Not confirmed for legacy MCX variants. So this SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB is specifically designed and listed for the MCX SPEAR LT platform. Also, earlier MCX Virtus and legacy MCX models use different upper receiver configurations that may not accept SPEAR LT barrels without modification. Therefore, verify compatibility with your specific MCX variant before ordering if you’re running anything other than a current SPEAR LT.
Who is this SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB best for?
This SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB fits MCX SPEAR LT owners doing a caliber swap from 5.56 to .300 BLK, or replacing a damaged factory barrel. So if you already have an MCX SPEAR LT pistol or registered SBR in .300 BLK and need a factory-correct replacement barrel, this is the right part. Also good for builders adding a short .300 BLK upper to an existing MCX pistol-configured lower.
Specs Table
| Spec | Detail |
|---|---|
| SIG Part Number | 8901315 |
| Compatibility | SIG Sauer MCX SPEAR LT, .300 Blackout configuration |
| Caliber | .300 AAC Blackout |
| Barrel Length | 9″ |
| Material | Stainless Steel |
| Thread Pattern | 5/8×24 |
| Gas Block | Adjustable, complete assembly included |
| Condition | New in Box (NIB) |
| NFA Warning | Only for pistol-configured lowers (no stock, not recorded as rifle) OR BATFE-registered SBR lowers. All NFA rules apply. |
| Installation | Gunsmith recommended (SIG recommendation) |
| Best For | MCX SPEAR LT suppressed .300 BLK pistol builds, SBR caliber swaps |
| Weight | verify |
| Price | $700 |
FAQ
Can I install this SIG SAUER MCX SPEAR LT 9.0″ 300 BLACKOUT W/ GAS BLOCK NIB on my standard MCX rifle lower? No. SIG states this barrel may only go on a pistol-configured lower (no stock, not recorded as rifle) or a BATFE-registered SBR. Installing on a rifle lower without SBR registration violates NFA law.
Does this barrel include the gas block? Yes. The complete gas block assembly ships pre-installed with this barrel.
Is the gas block adjustable? Yes. The adjustable gas block is a key feature for running subsonic .300 BLK suppressed without excessive gas pressure.
What thread pitch does this barrel use? 5/8×24, the standard .30 caliber thread pitch for suppressors and muzzle devices.
Will this barrel fit a legacy MCX Virtus or older MCX models? Not confirmed. This barrel is specifically listed for the MCX SPEAR LT. Verify compatibility with earlier MCX variants before ordering.
Do I need a gunsmith to install this barrel? SIG recommends installation by a qualified and trained gunsmith, though MCX barrel swaps are user-friendly by design.
Is this barrel stainless or carbon steel? Stainless steel construction, confirmed from SIG and multiple retailer listings.
Find more genuine SIG Sauer MCX SPEAR LT barrels and .300 Blackout accessories at gunpartspalace.com.
