RE: vent. ribs
the purpose of a rib on a barrel is to make you eye run down the barrel faster than w/o one. your eyes can distinguish flat surfaces easier than round ones.( at least as far as aiming shotguns go) its just an amming aid but not really a rear sight. with only a frount bead your eye itself becomes the rear sight thats how it was explaind to me, i had the same question once myself. ribs are more importaint for ducks and upland birds than turks. when your hunting turkeys your aimming your shotgun more like a rifle than a shotgun so a rear sight on your turkey gun helps a great deal.