Sig Sauer- SIG 516 Gen II Barrel: Chrome-lined, phosphated (or QPQ coated), military-grade barrel with a 1:7-inch twist rate; standard patrol models feature a 16-inch barrel. Caliber: 5.56/.223 Capacity: 30+1 Operating System: Short-stroke pushrod gas system that runs cleaner and cooler than standard AR-15 gas-impingement setups. Adjustable Gas Valve: 4-position gas regulator (1 = Normal, 2 = Adverse, 3 = Silenced, 4 = Off) to tune performance with different ammunition or suppressors. Receivers: Forged 7075-T6 aircraft-grade aluminum upper and lower receivers with a hard-coat anodized finish. Handguard: Free-floating M1913 Picatinny quad-rail forend for mounting optics, lights, and grips. Furniture & Controls: Features an M16A2-style birdcage flash hider, a telescoping multi-position stock (such as Magpul MOE or SOPMOD variants depending on the specific sub-model), and standard AR-15 ergonomics.