The Anderson Manufacturing B2-K004-AN08 is 16" M4 contour barrel that is designed for an AR-15 upper and has a carbine length gas system and a 1 in 8 twist. This barrel is constructed with 4150 Chrome Moly Vanadium.
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16 M4 Carbine Length Contour Barrel Chambered 5.56/.223 With A 1-8 Twist