I'm new at the XM15 stuff But when I bought my Shorty I picked the Heavy 16 inch Barrel over the others cause I wanted the most FPS and Accuracy! I have a Post Ban and I hated all the Muzzel Brakes that were on the SHORTY's!! MAN the AK47 is one UGLY Mo! Fo! and the other Post ban are just as Bad! Also I think the 16 incher would last longer than the M4 type (IMHO)!!