Ray B
AH legend
I read where John Olin had a M21 built with chokes designed for the left barrel to be fired first. The idea was that since he was right handed the recoil would push the gun slightly into the shooter and make for faster recovery than if the right barrel was fired first which would have pushed the gun slightly away from the shooter. With this in mind it seems to me that pressing the rear trigger and firing the left barrel first would make sense.