I cannot work out where they could practically draw the line? How can you possible ban all metalwork?
Anything that nerds in a nerd-rage might use as weapons on each other seems to be the rule. They have bouncers at the large events checking the stuff as you enter. So small stuff is ok, tools like dividers would probably not be allowed. Long sticks definitely not allowed. Functioning bows not allowed (strings have to be made of elastic so they won't actually work) or the limbs weak foam.
Makes it pretty difficult to make realistic-looking movie props that are solid enough for someone to carry around that also pass the rules. The cos-play manufacturer often stays at our house and our living room gets covered in bits of foam, paper, card, plastic, fabric while she is making stuff. She ships all over, it is amazing, gets orders from the USA, Canada, NZ. Guess it is because it is quite difficult to make it look 'real' when it has to made of foam, plastic and rubber.
The events are pretty amazing, and seeing what people make is impressive. I've seen someone in a full-size, absolutely realistic 'groot' suit (from guardians of the galaxy), an Iron Man suit they'd made themselves from fibreglass that looked identical to the movie; just about anything you can think of, it will be there.