As I understand it, the standard arrangement for double triggers on a side by side is for the front trigger to fire the right barrel and the rear trigger to fire the left barrel. Or if a single trigger, it selected the right barrel first, then the left barrel (based on the process that it is more natural for the shooter to press the front trigger, then continue the motion of his finger to the rear trigger). When John Olin was having his company build Model 21s for him, he had them reverse...
Trigger Sequence
Trigger Sequence
