There are many 12 ga guns with wallowed out chambers and bores that people think are 11 ga guns. There is a Serialization Book and a research letter service that can be used to find original factory configuration.
TPS lists 11 ga guns.
A cylinder and improved cylinder choke set commonly results from a 2 inch bob at the muzzles, as full and fuller were the most normal chokes. The chokes also could have been reamed out. It is least uncommon that they came from the factory that way.
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