So a rifle must have a 16" or greater barrel length, measured from bolt face to muzzle, to remain NFA compliant. A <16" barrel can be used if a flash suppressor is permanently attached that brings the length up to 16". My question: is this "added length" limited to flash suppressors only, or can anything be permanently attached to the barrel that would bring it's length to 16" and still be compliant? For example, a bayonet fitted over the muzzle and welded in place.

Thanks for any help on this. For anyone curious, it's to settle an argument, not a planned project.