you said use nothing tighter than Improved...then you said so either a IC or Modified...im 99% sure that choke goes cylinder-Improved-Mod-Full..open to tightest. id use a cylinder...but heard improved works too but i dont know..i dont shoot slugs..to me i dont think choking a solid mass of lead is a brilliant idea..if it doesnt damage the barrel i dont think it would shoot well...so either IC or cylinder