There are two types of barrel selectors, inertial and mechanical, both automaticly select the other barrel after the first is fired. The differance is the inertial selector needs the recoil from the first shot to switch to the other barrel. If, after you check to make sure the gun is unloaded, point it in a safe direction any way, then check again to be really sure its unloaded, you squeeze the trigger twice and hear both hammers fall it has a machanical barrel selector, if you hear the first hammer fall but not the second give a good thump to the recoil pad then try the trigger again, you should hear the second hammer fall and you would have an inertial barrel selector. Most shotgunners try to shot the bottom barrel first because the recoil is more straight back which most shooters have an easier time controlling for a faster fallow up shot.