Re: air rifle supressor
"Numerous paintball silencers tested by the Firearms Technology Branch have been determined to be, by nature of their design and function, firearm silencers as defined in 18 U.S.C., Section 921(a)(24). "
This statement is not very clear. It says "numerous" but not all. I am guessing that any silencer that is detachable could be placed on a firearm and if the there is a one decibel reduction in sound it becomes a silencer.
But I am still not sure how a paintball silencer would differ from the muffler placed on a lawnmower. You might be able to find one that could go on a rifle barrel and look out your lawnmower has an illegal silencer.
Marine engine mufflers I believe are also called silencers. If I am wrong I would like to be corrected. If the BATFE could classify a shoestring as a machine, than anything is possible.