AR15 / M16 A3 Complete Parts kit LESS lower receiver, with 16" inch M4 contour barrel and A3 Upper receiver. Item # AR-RKM4A368. This 6.8 SPC caliber barrel is 16" long, threaded the standard 1/2 x 28 tpi, and has an A2 flash hider with the correct crush washer. The barrel has a forged A2 front sight base with bayonet lug, not the cheaper cast front sight base which can break. It sports M4 contour and length handguards with full heat shields, and a correctly sized gas port for reliable function. The barrel is machined from chrome-moly, high vanadium steel and hardened to a U.S. government Mil-spec of Rc 26-32. The barrel, and all external steel parts, are manganese phosphate finished IAW 5.3.1.2 of Mil-STD-171, the U. S. government's recommended protective finish for steel. This finish not only looks great, it affords complete corrosion protection. These barrels are of Mil-spec M4 contour (.750 under the front sight base) complete with the M203 groove in the front. This contour is the perfect balance between light weight, heat dissipation, and accuracy. The barrel is button rifled with 6 grooves, right hand, 1 / 10" twist. The 1/10" twist is best for this caliber because it handles the widest variety of ammunition and bullet weights. The barrel is mounted on a FORGED A3 upper receiver with built in Mil-spec M1913 Picatinny accessory rail, with the correct rail numbers engraved, made from certified 7075T6.511 alloy forgings, hardcoat anodized IAW Mil Spec A8625, Type III, Class II, black per No. 37038, Table IX with nickel acetate seal, as per the Mil-spec. The upper features a forward assist and hinged ejection port cover. The buttstock is the current US Mil-Spec M4 buttstock. This buttstock features 6 positions for maximum shooter comfort, reinforced "honeycomb" design for heavy duty use, the correct M4 lock nut, and standard lock plate. All semi auto lower receiver parts are INCLUDED as well as semi auto bolt, carrier, and charging handle. The upper is COMPLETELY ASSEMBLED, and HEADSPACED. Everything you need EXCEPT the stripped lower receiver! (A complete firearm is pictured, the lower receiver and magazine, even though shown in the picture, are NOT included) Add $50 for CHROME LINED barrel and chamber, BlackthorneProducts.com uses FIRST quality parts ONLY , NO "seconds", EVER. Since this parts kit does not include the receiver, no FFL is required. $20 shipping to continental US, +3% for non-certified funds. Manufactured by BlackthorneProducts.com