Machinegun Forum. ATF: National Firearms Act (NFA) forum. Talk about machine guns, short barreled shotguns (SBS), short barreled rifles (SBR), or destructive devices (DD). All State, Local, and Federal Laws apply. Only discussion regarding legally registered and transfered NFA items allowed. No discussions regarding how to build an unregistered NFA item, blueprints, or parts will be tolerated. Violation of these rules will be reported.