Sig Sauer MCX Spear LT .300 Blackout
Model: RMCX-300B-9B-LT-SBR
Sig Sauer MCX Spear LT .300 Blackout
Model: RMCX-300B-9B-LT-SBR
Full Specifications
Threaded 5/8x24 barrel: compare .30 caliber suppressor prices.
About This Firearm
The Sig Sauer MCX Spear LT is a 9-inch short-barreled .300 Blackout built as a suppressor host for close work. It has an MSRP of $2,179. A gas piston drives the action instead of a gas tube, and the gas system adjusts, so the rifle can be set for subsonic loads behind a can and turned back up for supersonic.
No sights are fitted and none are named for this configuration. The barrel ends in a 5/8x24 thread under Sig's QD suppressor-ready flash hider, so a Sig can locks straight on and anything else screws to the thread underneath. The Folding Minimalist Plus stock folds and collapses, taking a 27.75-inch rifle down further for a bag, and the controls work from both sides. One 30-round magazine comes in the box and the well is AR-15 pattern. This is a short-barreled rifle, so it takes an NFA tax stamp to buy.
If you're cross-shopping, the Sig Sauer MCX Rattler is a used buy at 5.70 lbs, 0.70 lbs lighter, on a 5.5-inch barrel at 23.5 inches overall, which packs smaller and gives up more velocity. The CMMG Dissent Mk4 has an MSRP of $2,149.95 and matches this rifle's 6.40 lbs, but its 16.1-inch barrel and 35.5 inches overall make it an ordinary rifle purchase with no stamp. Sig lists the Spear LT barrels as interchangeable, so one receiver can carry a short host and a longer barrel at different times.
Best For
Strengths & Limitations
- Sig secures the flash hider with Rocksett, so the muzzle device does not back off under a suppressor's weight.
- The trigger is Sig's Flat Blade Match unit, not a mil-spec single stage.
- Sig describes the handguard as lightweight and ergonomic, and it is M-LOK, so a light or a laser mounts without an adapter.
- Nothing on the rifle can be aimed as it comes, so an optic is part of the purchase.
- One magazine ships with it, and a .300 Blackout carbine gets through more than one in a session.
- This configuration comes in a Coyote finish, so matching accessories means buying coyote or living with a two-tone rifle.
Compatible Ammunition
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Frequently Asked Questions
Will AR-15 uppers or bolt carriers fit it?
No. The MCX is Sig's own system with a gas piston, so AR-15 uppers and carriers do not swap in, even though the magazines do.
How does the 5.56 Spear LT differ in barrel spec?
Sig gives the 5.56 rifle a 1:7 twist and a 1/2x28 thread, where this .300 Blackout barrel is 1:5 with 5/8x24, so muzzle devices do not move between them.
What does the stock adjust?
It folds to the side and its length adjusts, so the same rifle fits a shooter in armour and a shooter in a shirt.
