As far as which barrel to shoot first, have the barrels checked for choke size, unless that info came with the gun. Most people would opt to shoot the more open of the two chokes first.. i.e. Modified before full, etc.., using the theory what you are shooting at is usually closest to you for the first shot, leaving the fuller choked barrel for the further shot should you miss and the object is now further away. Should they both be choked the same (which I doubt, unless it is barreled as a trap gun), shoot whichever barrel you are more comfortable with.