12 ga Choke size

[Kroy]

Question, what should be the muzzle opening size for a 12ga using 0,00,000 and or slug ?
My camp gun has a 20" barrel with a removable choke that has been machined out and before I try slugging it, I would like a little discussion on the matter.
Thanks

 

[Winchested]

Start with improved cylinder for slugs and go up or down from there and start at full for buckshot.