Shouldn't be any trick to tell gauge. But looking at the photos, I have to say this: It can't possibly be a case of Remington having made 20ga barrels and fitted them to 40 year old Model 1889 12 or 16ga receivers someone found sitting around the plant. Were that the case, the chambers would look much smaller and the chamber walls much thicker, in order to get 20ga barrels to fit on a larger gauge receiver.

Ted, you may be thinking of Nilo Farms in Illinois. That was a Winchester operation. I don't recall reading about anything in Ohio run by Remington. Seems I have vague memories of something out in Delaware, which would've made more sense given Dupont's location.