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Aero Precision M4E1 Threaded PRO 13.7in 5.56 w/ATLAS R-ONE Handguard Complete Upper Receiver with Flash Hider has been discontinued by Aero Precision and is no longer available. Our product experts have helped us select these available replacements below.You can also explore other items in the Gun Parts, AR 15 Parts, Rifle Parts, AR15 Upper Receivers yourself to try and find the perfect replacement for you!
ATTENTION! We currently do not ship this product to AK, CA, HI, IL, NY, WA, P.O. Boxes, and U.S. Territories. Please see our policies for more information.
The PRO Upper Receiver Group built around our PRO 5.56 Cold Hammer Forged Barrel that is paired with our PRO 5.56 BCG. Included ATLAS R-ONE Handguard, BREACH Charging Handle, and VG6 Delta muzzle device round this assembly out into a premium turnkey solution for your next build.![]()
Cold hammer forging differs from other common barrel manufacturing processes. Rather than drilling a blank and using cutters, buttons, and reamers to machine the chamber and rifling into the barrel, a cold hammer forged barrel is made by forming the barrel around a mandrel that has the rifling inclusions precision ground into it. This process is referred to as cold hammer forging because the process is done at room temperature and the metal is not heated.



