This Dirty Bird Industries Complete Upper features a Black Nitride 16"" Sub-MOA Government Profile barrel chambered in 5.56 with a 1:7 twist. Built on a top-tier t-marked Forged Upper Receiver and finished with Dirty Bird's 15"" SMRS M-LOK Handguard available in several color options. No corners are cut when manufacturing these complete uppers. All barrels are dimpled and cold blued, use a black nitride 4140 steel gas block and a stainless steel gas tube. The gas block set screws feature knurled cone tops and are installed using blue locktite ensuring that no amount of firing will cause the set screws to come loose but they will still able to be removed for servicing if needed.NEW: The Dirty Bird SMRS Handguard featured our new Rock Solid Patent Pending Anti-Slip / Anti-Lift attachment system. The clamp-on style of handguard attachment, utilized by many manufacturers is both secure and convenient but one problem has always been that clamping the handguard it tends to lift the front end of the handguard. The longer the handguard, the more drastic the effect. If you've ever had to bottom-out the front-sight post of a rail mounted BUIS in order to get the correct elevation, the issue is probably due to this ""lift"" phenomena.Made in the USA - Backed by Dirty Bird Industries' Limited Lifetime WarrantyBarrel Chambered in 5.56 (will also function with .223) 16"" Government Profile w/ 1:7 Twist Mid-Length Gas System Black Nitride Finish High Pressure Tested and Magnetic Particle Inspected Sub-MOA GuaranteeBolt Carrier Group Designed for use with both 5.56 and .223 Strategically relocated load bearing surfaces reduce carrier tilt/can't during recoil, thus increasing reliability and longevity Additional wall thickness in the gas exhaust port area for added strength and rigidity High Pressure Tested and Magnetic Particle InspectedHandguard Tough Machined from aircraft grade 6061-T6 aluminum extrusions. Anti-rotation tabs. Type 3 hard anodizing or Cerakote sprayed at 1 mil thickness per spec. Versatile M-LOK attachment slots on all sides (except top) 1913 Picatinny top rail with shaved and beveled center section. Raised QD attachment points at the 3 and 9 o'clock positions. Snag free design with smooth, uniform octagonal surface ideal for accessory attachment or application of specialty coatings or patterns. Practical Aircraft Grade aluminum barrel nut. In our tests, the aluminum barrel nuts are just as effective when torqued to spec. Additionally, the weight savings enable us to utilize a longer barrel nut design which means more surface area at the attachment point without adding unnecessary weight.Upper Receiver Precision Machined from Top Tier 7075-T6 Aluminum Forgings (forge marks may vary) Not all foged uppers are created equal and we only use the best for our uppers meaning they will be free from excessive pitting, machined to spec and finished with quality (not purple or chalky) hard coat anodizing M4 FeedrampsCharging Handle Mil-Spec Style 6061-T6 Billet Aluminum Smooth Operation and Positive Grip under Extreme Conditions Type 3 Class 2 Hard Coat AnodizingAvailable Handguard Colors: Black, Magpul FDE, Magpul OD Green, Midnight Bronze