Dfariswheel,
Nailed it.
One has to pattern their own gun. Makes no difference what a bbl or choke is marked , only the pattern board will define what YOUR Gun throws WHAT loading for a given TASK.
Even two guns identical using identical loadings can and will shoot different.
Dfarris - gave a best general rule - that being ~ 15 POC [ Imp. Cyl] "tends" to work well. IME - across the board in a variety of guns/ bbls/ POCs from 25 - 15 [ Mod to IC] the 9 pellet 00 Win or Fed loading works "best across the board'. Not saying there are not some better- only as a reference, kinda like the markings on chokes and bbls.
Win/ Fed 1oz Forster slugs from a IC, smoothbore.... Win/ Fed for #4 buck .
Time for buying a 5 pk of a bunch of slugs and buckshot.
I also recommend Bob Bristers' book "Shotgunning: The Art And The Science.
www.abebooks.com
matter of bore , not choke- Brister