ZEVON, One gun i have started out a 30 inch full choke Remington 870 . IT was a pain to hunt with in tight cover . I met a gunsmith while shooting IMHSA that said he could fix me up . he cut the bbl to 23 3/4 inches ( worked out with the rib support ) . he miked the bbl and installed a long choke tube , the tubes are long but flush . he has notes as to what tube works best with each inside bbl dimension . to get a pattern that a ball cap will cover at 40 yards it takes a XX full in my gun . It also requires Federal 000 copper plated buck . He would take a tube and alter it to match the bbl. this gunsmith now makes his own tubes . It is not a buy a tube and get a tight pattern , sometimes the tube is altered , sometimes the forcing cone is lengthen and a few other goodies he keeps to himself . I live in Va. and turkey shoots are big time so barrel work is big time . There are several smiths that can do this work some tube a bbl some sleeve it .
on the other end there are guns around here that will put 100 plus #9 shot in a 5 X5 card at 28 yards , and some that will do better ! Keep in mind the barrels cost more than a gun sometimes .
I backed off to a full and sometimes x-full choke for my gun so i could have a useful pattern !
That gunsmith has most likely saved more deer lives than PETA could dream of doing ! Try hitting a running deer at 40 yards with a ball cap !