The SIG Sauer MCX-SPEAR LT IR .300 Blackout is a 9-inch short-barreled rifle in flat dark earth with a folding stock (SIG Sauer part no. RMCX-300B-9B-IR-SBR). The barrel uses a 1:5 twist for the heavier bullets common in .300 Blackout, and the rifle runs a gas piston system. It measures 27.8 inches overall, short enough to stow easily with the stock folded. It is semi-automatic, holds 30 rounds and ships with one magazine. Pair it with a suppressor and subsonic ammunition for a quiet, compact rifle for home defense or the range.

Key Specifications

• Chambering is .300 Blackout, a cartridge that runs supersonic and subsonic loads.
• Barrel length is 9 inches, a good balance of velocity and compactness for this cartridge.
• Rifling twist is 1:5, matched to heavier subsonic bullets.
• Overall length is 27.8 inches, compact for a stocked rifle.
• The stock folds, shortening the rifle further for storage and transport.
• Capacity is 30 rounds, a full-size magazine.
• It ships with one 30-round magazine, ready to load.
• The action is semi-automatic, one round per trigger pull.
• The operating system is a gas piston, which keeps combustion gas out of the receiver.
• The finish is flat dark earth, a tan color suited to field use.

Frequently Asked Questions

Can it run suppressed? Yes. .300 Blackout and a gas piston system are a natural suppressor pairing, and the 1:5 twist stabilizes heavy subsonic bullets.

Do I need ATF approval to buy this? No. As of October 9, 2026, ATF no longer requires Form 4 approval, registration or a tax stamp for short-barreled rifles. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply. Taking an SBR across state lines still requires an approved ATF Form 5320.20.

Does the stock fold? Yes. The folding stock shortens the rifle below its 27.8-inch overall length for storage and transport.

Buy the SIG Sauer MCX-SPEAR LT IR .300 Blackout SBR, 9-Inch

As of October 9, 2026, this short-barreled rifle transfers on a Form 4473 with a background check at your Class 3 (SOT) dealer, with no Form 4 or tax stamp; state and local laws still apply. Order through SIG Sauer‘s short-barreled rifles lineup and our Lubbock, Texas team will handle the transfer, and it ships fast to your Class 3 dealer. Short, quiet with the right can and finished in FDE, it is a rifle built to go everywhere.