This complete upper includes the best features including; the fluted accuracy potential enhancing 223 Wylde chambered and QPQ treated stainless steel barrel, the acclaimed ATLAS R-ONE Handguard, and the every popular and stylish M4E1-Threaded upper receiver.Fire match accurate 223 Remington specification ammunition while maintaining the safety and reliability capability of 5.56 NATO specification ammunition, a winning combo at whatever contest you enter.FeaturesM4E1 Threaded Upper Features: New enhanced forging that gives the upper receiver a "billet look" New picatinny profile that blends seamlessly with our Enhanced Series Handguards M4 Feedramps .250" takedown pin holes Laser engraved T-marks Includes port door and forward assist installedATLAS R-ONE Handguard Features: Full top picatinny rail for optional attachments Quick disconnect sling socket at the 3, 6 and 9 o'clock positions Compatible with low profile gas blocks 1.3" Inside diameter 1.5" Outside diameter Compatible with mil-spec AR15 upper receivers and barrels Learn More about our NEW ATLAS Handguards18" .223 WYLDE STAINLESS STEEL QPQ BARREL, RIFLE LENGTH FEATURES: .223 Wylde 18" Rifle Length Barrel, 1/8 Twist QPQ Corrosion Resistant Finish .750 gas block journal Rifle length gas system M4 Feed Ramp Extension HP and MPI tested Standard A2 flash hider