I do need to try some other slugs. I just did a web search, and the tables at this site
provide enough detail to "guesstimate" the choke simply by measuring the diameter of the bore just inside the muzzle. My 24's barrel gauges at 0.587, indicating full choke. I guess to be precise, one would need to measure the length of the constriction (choke) and the diameter of the bore in front of the constriction, but I'm not sure what I'd gain by that ... unless the choke proved to be too short, in which case I'd have a different problem to solve.