With my .450 Jeffery, shooting either barrel first works the same for regulation and groups.

There was a problem with the triggers when a reputable gunsmith looked at them. They were set extremely heavy and whatever else he felt needed changing to adjust them for better use.

I try to use the left barrel, rear trigger first. Even if that is not ideal. Yep the front trigger, right barrel should be first but ...

I noticed a video not long ago where the shooter was shooting the rear trigger first.

The thing is, if the rifle regulates OK with either barrel, only test shooting it will provide this information, if shooting say an elephant, and using the front trigger and you double, your rifle is empty and it is more dangerous than shooting the rear trigger, and having a back up round.

YES I know, it is supposed to be front trigger/right barrel first, but ..... I also know that a LOT of clients DOUBLE their rifles, but FEW admit it.

Also there are examples of some double rifles where the left barrel was designed to be shot with precision at longer ranges. Correct or crap? Don't know, just armchair reading from the net. Maybe someone can say Yay or Nay?