Upper Receiver Assembly 223 Gen 4, Black, 11" M.R.R. Barrel: - 16.5" - Weight: 5.3 lbs - Overall Length: 23.75" - Match grade barrels fluted to reduce weight and dissipate heat. - 4150 Mil-B-11595E chromoly alloy. - Corrosion resistant nitride heat-treated 1:8. - POF-USA triple-port muzzle devices. - POF-USA oversized heat-sink barrel nut. - 5.56x45 mm NATO (.223 Remington) chamber. - E dual-extraction chamber technology (GEN 4 ONLY). Method of Operation: - Semi-auto (P415) or full-auto select-fire (P416) rotating bolt, short-stroke gas piston system. - Corrosion resistant nitride heat-treated gas piston system consisting of a single piece gas block, gas plug, gas piston, and operating rod. - Multi-position regulating gas system with normal, suppressed, and bolt-action (off) operating modes. Bolt & Carrier: - Nickel plated bolt carrier with integrated bolt carrier key. - POF-USA roller cam pin with chrome plated stem and NP3 roller. - Chrome plated bolt. Upper Receiver: - POF-USA patented Modular Railed Receiver (M.R.R.); free-floating monolithic rail system. - Billet machined 7075-T6 aircraft aluminum alloy. - 2-piece upper receiver. - Black anodized billet charging handle. Handguard: - POF-USA free-floating modular, aluminum handguard. - Integrated picatinny rail-estate for 10" and 7.25" barrels. - Black Anodized Manufacturing: - All raw materials, heat-treats, platings/coatings, accessories, and component parts on our weapon systems are made 100% through U.S. owned and operated steel mills and manufacturers. Upper Receiver Assembly 223 Gen 4, Black, 11" M.R.R.