Maybe they changed the trigger assembly in a gun that already had a choked left barrel. Not my experience, but J. Nickerson in "A Shooting Mans Creed" gives a good description on how this type of shotgun is used. They are meant for incoming driven grouse in Britain or red partridge in Spain, where you start early with the choked barrel and the open barrel comes next, then you change guns, so the open barrel goes first and the choked second on the departing flock. Four birds in your bag.