Falcon5NZ:...Anyway, I have two questions about the US Legal implications of this.
Firstly, Could possession of tape and an empty plastic bottle be called constructive intent if they really wanted to throw the book at you?
Secondly, Would the bottle cap or the actual bottle be considered the suppressor? E.g I know a threaded barrel could be used for a muzzlebrake or flash suppressor and in itself not illegal but the suppressor that attaches to it requires a Class 3 Permit.
This is not constructive intent, but constructive possession.
The plastic bottle is considered the supressor if used as such.
There used to be an ad in Shotgun News for an adaptor that allowed you to screw a 2liter plastic bottle to the end of your barrel for a cheap supressor. The adaptor was and is completely legal to own. Just as empty (or full) plastic bottles are legal).
Constructive possession might apply if you possess the adaptor, a plastic bottle and a firearm.
The fact is there are many everyday items that could be used to make a homemade supressor. It would be much more difficult to prove in court that a common household item such as duct tape was intended for use illegally than if the defendent possessed that little adaptor from Shotgun News.