Typically, if the front trigger is fired 1st, which barrel was fired?
usually the right barrel, if the barrels are fixed chokes the right one is the more open choke
For nearly all doubles, the front trigger fires the right barrel and the rear trigger fires the left barrel. For over/under shotguns with two triggers (Merkel 200s for example), the front trigger generally fires the lower barrel and the rear trigger the upper barrel.