This AR-Stoner M4-Contour AR-15 Barrel is fully chambered and ready for installation onto a host upper receiver. The barrel features a true 5.56x45mm NATO Chamber for use with both commercial and military surplus ammunition, while the 1 in 7" Twist Rifling is capable of stabilizing light to medium weight projectiles of up to about 77 grains. This barrel is an excellent choice for a low budget, general purpose AR rifle build that's perfectly suited for use at the range, in a 3-Gun match, or in the field pursuing game. Barrel extension and locator pin are both included and factory installed.