Primary Weapon Systems MK116 223 Wylde 16 Inch 4140 Steel Chrome-Lined Black Hard Coat Anodized Barrel Finish. 56mm NATO and .223 Remington with the Primary Weapons Systems MK114 MOD 1-M UPPER .223 WYLDE Upper Receiver These AR15 Upper Receivers will give you the AR15 build you've been dreaming of. This complete upper includes all kinds of proprietary extras like the PWS Long Stroke Piston System and PWS Piston Upper. The PWS M-Lok handguard allows you to add any lights or attachments your heart desires. Now's the time go Wylde Available with or without a compensator. Specifications for Primary Weapons Systems MK1 MOD 1-P Upper Receiver: Product Color: Black Features of Primary Weapons Systems MK1 MOD 1 Upper Receiver: ADJUSTABLE GAS BLOCK SMOOTH RECOIL IMPULSE THE PWS LONG STROKE PISTON Package Contents: Primary Weapons Systems MK1 MOD 1-P Upper Receiver