Like that ever made any difference to the ATF. A suppressor is considered a firearm. Yes, it doesn't shoot, but it still counts.
The ATF considers suppressors to be firearms, because the law says plain as day that suppressors are firearms, not just because of some ATF interpretation.
§ 921. Definitions
(a) As used in this chapter
...
(3) The term “firearm” means
(A) any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive;
(B) the frame or receiver of any such weapon;
(C) any firearm muffler or firearm silencer; or
(D) any destructive device. Such term does not include an antique firearm.
I'm not a lawyer, but that seems pretty obvious to me.
As for the question of whether briefcases and holsters can be AOWs, or whether an AOW only exists when those objects are used in conjunction with a firearm;
again the law is pretty clear:
§ 5845. Definitions
For the purpose of this chapter
..
(e) Any other weapon
The term “any other weapon” means any weapon or device capable of being concealed on the person from which a shot can be discharged through the energy of an explosive, a pistol or revolver having a barrel with a smooth bore designed or redesigned to fire a fixed shotgun shell, weapons with combination shotgun and rifle barrels 12 inches or more, less than 18 inches in length, from which only a single discharge can be made from either barrel without manual reloading, and shall include any such weapon which may be readily restored to fire. Such term shall not include a pistol or a revolver having a rifled bore, or rifled bores, or weapons designed, made, or intended to be fired from the shoulder and not capable of firing fixed ammunition.
When someone has a piece of leather or a briefcase that can discharge a shot, then they'd have an AOW. Until then, it's the combination of a holster with a trigger cutout and a pistol, or the combination of firearm and a operational briefcase that are AOWs.
