Due to the quick barrel, the vehicle-15 SMGs experienced from a loud and bright muzzle blast, and a variety of muzzle devices were developed to reduce this. The SMGs were at first equipped with the regular M16 rifle's "duckbill" or a few-prong flash hiders, which did not reduce the problem. In September 1966, Colt made a 3.5-inch (89 mm) extended