The top of your bolt provider teams. The very best could be the standard five.56mm bolt provider group. Recognize the bolt, cam pin and also the provider vital. On the bottom will be the 9mm SMG bolt group. Anything shorter than a 16-inch barrel is considered a brief barrel rifle, https://andyetdmi.verybigblog.com/26486640/detailed-notes-on-colt-9mm-upper