The Sig Sauer PM400 features a Direct Impingement Gas Operating System with Rotating Locking Bolt, Flip-Up Sights, Integral Ambi QD Sling Mounts, Aluminum KeyMod Rail, and SBX Pistol Stabilizing Brace. SIG's SBX Stabilizing Brace will give improved accuracy and reduced recoil when shooting an AR-pistol with buffer tube. The unique design uses the forearm to provide a natural and comfortable rest for shooters of all sizes and physical ability.