Sig MCX Spear-LT 9" .300BLK

The MCX-SPEAR LT IR 9-inch .300 Blackout SBR is the factory-stocked SKU RMCX-300B-9B-IR-SBR. Its short-stroke piston drives the action, while a separate carriage and recoil assembly stays inside the upper receiver. That assembly eliminates the conventional AR buffer and receiver extension, so the Folding Minimalist Plus stock can fold without disabling the action.

SIG's current manual gives the two-position gas valve exact ammunition and suppressor roles. One position covers subsonic ammunition with a suppressor and adverse conditions. The other covers supersonic ammunition with or without a suppressor. SIG warns that subsonic ammunition is not designed to cycle reliably without a suppressor and that the higher-gas position does not guarantee it.

The exact current product page lists a 9-inch cold-hammer-forged barrel, 1:5 twist, 6.4-pound weight, 27.8-inch overall length, Folding Minimalist Plus stock, and fully ambidextrous controls. The fast twist adds stability margin for long, heavy subsonic bullets. This stocked short-barrel configuration is a factory SBR, so federal registration and applicable state and local limits remain part of the ownership decision.