So would they accept a zip gun? How about one of those cheap .44 caliber black powder derringers made from a kit? Or a gas pipe shotgun?Where’s the logic in the line they have drawn?
A good question. No one will know for certain until they try. The police at these events are usually pretty good at letting anything which is plausible in. It is not their money, and why cause a problem? Everything is supposed to be destroyed anyway.
They sometimes raise an eyebrow to someone bringing in dozens of guns at one time, or lots of homemade guns.
I have not heard of anyone being arrested at one of these events.
Most private buyers know the rules, know the law, know their rights, and are careful, polite, and persuasive.
Logic? The logic is purchasing lots of cheap "ghost guns" for many times what it costs to make them shows the event to be logically indefensible. The primary purpose of these events is for street theater, to send the message: guns are bad, turn them in!
Private buyers neutralize that message with their own: Guns are valuable, I pay cash!