Factory New - comes with a 16" lightweight barrel with M-LOK rails. This AR57 AR57 Upper Receiver Assembly converts any AR-15 lower to a rifle capable of shooting 5.7x28 ammunition. The unique upper design of these AR15 Upper Receivers loads from the top and ejects downward through the AR-15 mag well. The new generation upper has a stronger, lighter, and more streamlined rail; finished with a beautiful ultra-smooth melonite black coating. Convert your AR-15 type rifle to shoot the same 5.7x28 ammo as the legendary FN P-90 PDW! This AR57 Upper is constructed with a steel barrel, muzzle brake, bolt carrier group, buffer, and screws, all built into an alloy monobloc receiver. In other words, it is ready to drop in and push pin. It is also built as solid as a tank. A single block of Aircraft Grade 7075 T6 aluminum, referred to as Kryptonite Monobloc and rated at 83000 PSI strength, is used for the receiver and its component rails. Precision milled to within .002 tolerance, this upper is chambered in 5.7 x 28 mm. The barrel is 16 inches with a perforated muzzle brake attached on 1/2 x 28 threads making the overall length 18 inches; the bore is six groove right hand 1:8.5 FN twist. The sight system is a 13 slot Picatinny over the operating handle, with 3-slot upper and lower forward rails. The metal parts, including receiver, rail, barrel, and bolt, are melanite treated for a hard, durable finish. Bolt is made from 8620 alloy. The receiver and rail block measures just over 17 inches overall length; from the receiver back to the muzzle end, the total length is 24 9/16 inches. In contrast to many other receivers, there is no gas system to become clogged with carbon or fouling; the chamber stays clean well beyond extended shooting. Extremely reliable, simplicity is key, with the free sliding bolt being the only moving element and its easy removal makes maintenance literally a snap. The AR-57 system ejects spent rounds through the lower's magazine well. *Does not include the magazine. Specifications for AR57 ULT 16in Barrel 5.7x28mm Upper Receiver Assembly: Manufacturer: AR57 Cartridge: 5.7x28mm Overall Length: 18 in Barrel Length: 16 in Threads per Inch: 1/2x28 Fabric/Material: 8620 Alloy Gun Rail: M-LOK Gun Type: Shotgun Condition: New Package Contents: AR57 ULT 16in Barrel 5.7x28mm Upper Receiver Assembly