The AR-15 20-inch Flat Top Bull Barrel Upper Assembly includes the complete barrel assembly, a forged and hard coat anodized flattop upper receiver, ejection port cover, forward assist, M4 feed ramps, A-2 Standard Free Float AR-15 Handguard (12.5" Length) and a 1 in 9 twist. The barrel has an 11-degree target crown.

The M4 cut extends down beyond the edge of the barrel extension (has a scalloped appearance), and a correspondingly deeper cut in an M4-spec upper receiver effectively extends the ramps downward (they're lowered).

The primary purpose of a firearm muzzle crown is to provide propellant gases a resistance free path away from all parts of the projectile as it exits the bore of the barrel. The secondary purpose is to protect the bore from damage caused by misuse. The third purpose is for good looks which is always achieved when the primary purpose is satisfied.

The muzzle of the 11-degree crown is sunk at an angle of 11 degrees from square (79 degrees of barrel). The 11-degree angle extends either the full muzzle radius or the greater part of muzzle radius. The exact angle sometimes varies a degree or two from eleven and is still referred to as being a target crown but through experimentation and time eleven degrees is normally accepted as the optimum universal angle for this type of target crown.

1-in-9 Inches Twist Rate

The 1-in-9 is a great compromise twist rate-not too fast to cause problems with the 55-grain bullets, but fast enough to stabilize all but the heaviest bullets under most circumstances. The 1:9 barrel is best for stabilizing lighter and mid-weight bullets between 45 and 77 grains.

No FFL required and easy installation - remove 2 pins, insert upper, and replace pins.

This upper assembly does not include threads for a flash hider and no bayonet lug.

Bolt Carrier and Charging Handles are Sold Separately.