Many good points made here. That being said, what's stamped on the barrel can be misleading. For example, I have an Ithaca NID 20ga marked 2 and 4 (M/F) . . . except my bore and choke gauge tells me that it has no choke in the R barrel, mid-teens in the L. So C/M, which is fine with me--but clearly tampered with somewhere along the line.
Then there's also the issue that different manufacturers use different criteria for chokes. I have a 20ga Bernardelli that's stamped 4 stars and 2 stars, which by Italian choke markings should mean IC/IM. Bore constrictions are .011/.029, which is more like skeet 2/extra full. The old Belgian Brownings are notorious for having more constriction for the choke marked on the barrel than did most contemporary shotguns. Which is why it's always good to measure.
And older guns, in general, tended to have more constriction for whatever was marked on the barrels than new ones. That's because improved shotshell technology (plastic wads etc) produces tighter patterns in general than the old card/fiber overshot wads. So you shouldn't need as much constriction to produce that standard full choke pattern of 70% at 40 yards than your granddad did. Assuming high quality modern shells vs the best available 60 years ago.
