Rosco Manufacturing 16" M4 5.56 NATO (Mid-Length) Barrel Rosco Manufacturing 16" M4 5.56 NATO (Mid-Length) Barrel This 16″ M4 5.56 NATO Mid-Length barrel was designed around the USASOC specs for an Improved Upper Receiver Group with a little bit of the OceanStateArmory touch as well. The longer gas... MSRP: Was: Now: $169.99 Add to Cart