I have 3 slug guns, one being a rifled 12 gauge 500. I get the best groups with the Lightfield Hybrids 2 3/4inch. I wouldn't think the rate of twist is any different in the barrel from a 20 to a 12?? Is this a rifled barrel your asking for or a smooth bore? A buddy of mine had a smooth bore and his shot Remington Sluggers the best.