Well, as long as I have been collecting firearms I had never made a class III purchase until recently when I acquired my first "destructive device" - a 12 gauge Streetsweeper. It was an unusual set of circumstances that led to acquiring that particular firearm and it will likely end up being mainly an exhibit for speaking engagements.
I received a lecture from the ATF agent when I picked it up about how peculiar these particular weapons are. I don't doubt it from initial inspections.