They make ammo for most ctg's. Buffalo Bore ammo is supposed to be quite good, however I've never used it, nor has anyone I know personally.
Seems to me Elmer Keith was a proponent of rear trigger first. Elmer wasn't a very big guy and had fairly small hands. He used to say you needed to shoot the gun to see if it regulated properly, firing the rear trigger first.
With multi-barreled guns, SxS and O/U I've always fired the right or upper bl.(front trigger) first.