A lot of people on this forum a whole lot more knowledgeable on this than me, but I'd say you generally have two rules of thumb: one being constriction related to shot size and one being constriction related to barrel takedown (i.e. an invector plus barrel at .742 likely won't be able to handle as aggressive a takedown as say a rem choke barrel at .727; to get both to .665, for instance, you'd have to take the invector plus down .077 whereas you'd only be taking the rem choke barrel down .062). With regard to shot size, typically less constriction for larger shot with regard to lead in particular (say a #5/#6 choke recommendation from a manufacturer might be .650 and for #4/#5 be .660), but with the newer shot like TSS a lot of folks prefer less constriction because of overall pattern density of shooting a 2oz load of #9s. No sense choking a load with 720+ pellets down crazy tight.
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