ADAMS ARMS BASE UPPER RECEIVER - MID-LENGTH - GOV'T. CONTOUR BARREL •Features M4 modified handguard •Self-cleaning short-stroke free-floating gas piston system features adj. gas settings resists corrosion expels carbon/gases forward & away from operator & eliminates harmonic barrel transfer flash signature & super sonic crack •1-pc. bolt carrier w/integral piston strike face •Mil-Spec forged 7075-T6 aluminum A4 flat-top upper receiver w/Type III Class 2 hardcoat anodized finish •1913 Picatinny top rail •M4 feed ramps •Laser-engraved T-markings •.750" diameter gas block •Chrome Moly Vanadium steel threaded barrel w/black Nitride anti-corrosive LifeCoat Melonite finish •No sights •Limited Lifetime Warranty Cal.: 5.56 NATO - Brl.: 16" - Muzzle Device: A2 Birdcage