I have a wonderful piece of Brass about 10 foot long and 13&1/2 inches wide with ( I'm guessing ) .125 thick.
I want to make a pair of megaphone exhausts out of it. The forming it will be no problem except is there any guidance as far as size I should be aware of? The inlet will be 2. 5 inches. The open end can be 4&1/2 inches across ( unless I roll the end slightly bigger) 
