HK MR556 AR-15 Flat-Top Gas Piston Upper Assembly 5.56x45mm NATO 1 in 7" Twist 16.5" Barrel Chrome Moly Matte with Quad Rail Free Float Handguard, Flash Hider
- Upper Receiver: MR556 Flat-Top
- Barrel Length: 16.5"
- Barrel Contour: Heavy
- Barrel Material: Hammer Forged Chrome Moly Steel
- Muzzle Thread Pattern: 1/2"-28
- Chrome Lined: No
- Barrel Finish: Parkerized
- Twist Rate: 1 in 7"
- Chamber: 5.56x45mm NATO
- M4 Feed Ramps: Yes
- Muzzle Device: A2 flash hider
- Gas System Length: Carbine, short stroke gas piston
- Gas Block Diameter: 0.750"
- Handguard: 9" Free Float Quad Rail
- Sights: None
- Extras: Carbine buffer spring and tungsten filled heavy buffer
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