29 thousands is a full choke
four inches of taper in a choke is not unheard of
as for charts - pick one
https://www.bing.com/images/search?q...tion&FORM=IGRE
but I am confused - a modern nominal 12 gauge is .729 - older Parkers were often a little over bored
are you saying that 4 inches from the muzzle - the bore diameter is .051?