DB shotguns require special fitting to make the two barrels thus their shot to converge at some predetermined range. The process is called "registration" and that's what adds so much cost to DB's. Sometimes they are "fitted" to an individual shooter, because shotguns don't normally have rear sights (the shooters eye functions as the rear sight and the gun is pointed rather than aimed) which of course adds expense.
Good info.
What then is the point of firing them off in the air from your 2nd story porch?
Asking for a FRiend....