L C Smith Buttplate and How do you determine Choke - 16 ga

Bought a 1921 Field Grade 'Fulton'in 16 gauge. Pretty slick with about 40% CC and otherwise all original except I'm thinking that the buttplate should have "L C Smith" molded in. Age wise, the present plain serrated plate matches very well and is matched to the gun.

Now the chokes. I can't see any markings under the barrel. If they didn't do so, can anyone tell me the nominal inside diameters for IC, Mod, and Full on a 16 gauge? :?:

Well, now I confused. The serial # is 43XXX and I just consulted my blue book and It lists 1921 and 1949 as possible manufacturers dates... :?:

From someone who has always wanted a Smith and now that moment has arrived!!!