More important to match the slug to your bore or rifling grooves, depending on what you are actually building. The loaded cartridge then has to be a drop-in fit to the chamber.

Most people say its best to get a mold to cast slightly oversize and push through a sizing die for uniform dia and concentricity.
Plastic shot-shell hulls are flexible and should take a .730 slug no worries, without sticking in a normal 12-bore chamber. I load .735 slugs routinely for a nitro paradox. I even made a hand-tool to flare the case-mouth slightly to make them easier to seat in the hull. Still roll-crimps onto the Fosbery shoulder just fine.