BudsGunShop.com - 4140 or 4150 ?

4140 Chrome Moly Steel specs Cartridge 5.56x45mm NATO Material Aluminum Barrel Length 16 Inches Twist 1:9 Inches Threads 1/2"-28 Barrel Contour Heavy Sights Yes Barrel Finish Black Parkerized Chrome Lined No Gas Block Diameter 0.75 Inches Gas System Length Mid-Length M4 Feed Ramps Yes Upper Receiver Type A3 Flat-Top Barrel Material 4140 Chrome Moly Steel Handguard 2-Piece Polymer w/Heatshield Bolt Carrier Assembly Included Yes Muzzle Device A2 Flash Hider Mil-Spec or Commercial Commercial

Gabe - The barrel is 4140 Chrome Moly Vanadiuml, with a 16" 1x9 twist, M4 Profile, Chambered in 5.56 Nato. The upper is a Flat Top Upper with White T-Marks & M4 Feed Ramps, and comes with a HPT/MPI tested Bolt and Chrome lined Carrier assembly, and Charging Handle. Includes CAR Handguards, and post front sight with bayonet mount. Considering it comes with the complete Bolt carrier group and charging handle, this is quite a deal, really. Just mount it on your complete lower, for an economical and quality built AR-15. Rated five stars by 10 different purchasers. See complete information at: del-ton.com/AR_15_Barrel_Assembly_p/dt1009.htm

Gabriel, This Del-Ton complete upper offers a 1 in 9" twist, 16" 4140 Heavy Chrome Moly 1/2"-28 threaded Barrel. (midwayusa.com/product/1003444487/del-ton-ar-15-mid-length-carbine-kit-556x45mm-nato-1-in-9-twist-16-heavy-contour-barrel)