The SIG Sauer MCX-SPEAR LT IR 5.56 NATO is an 11.5-inch short-barreled rifle finished in flat dark earth (SIG Sauer part no. RMCX-556N-11B-IR-SBR). Its barrel uses a 1:7 twist, and the rifle runs on a gas piston system. It is semi-automatic, holds 30+1 rounds and ships with one 30-round magazine. It feeds from AR-15 pattern magazines, so spares are easy to find. It is a compact, practical 5.56 rifle for home defense, training and suppressed range work.

Key Specifications

• Chambering is 5.56 NATO, a widely available cartridge for training and defense.
• Barrel length is 11.5 inches, a compact length that still gives 5.56 useful velocity.
• Rifling twist is 1:7, suited to a wide range of 5.56 bullet weights.
• Capacity is 30+1 rounds, a full magazine plus one chambered.
• 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.
• It feeds from AR-15 pattern magazines, so spare magazines are easy to source.
• The finish is flat dark earth, a tan color suited to field use.

Frequently Asked Questions

What magazines does it take? AR-15 pattern magazines, and one 30-round magazine ships with the rifle.

What twist rate does it use? 1:7, which stabilizes a wide range of 5.56 bullet weights, including heavier projectiles.

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.

Buy the SIG Sauer MCX-SPEAR LT IR 5.56 NATO SBR, 11.5-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. An 11.5-inch piston rifle in FDE is a sensible all-rounder for anyone who wants a compact 5.56.