You would really need to compare a 10 guage rifled slug barrel to a 12 gauge rifled heavy barrel not a shot barrel. I am sure they have different demensions. And you would have to take the measurement in the middle of the barrle some where, not at the end incase there was some sort of taper to it. I am sure the shot barrels have a different wall thickness regargless of guage.

You could be correct though. The 12 gauge may not simply be a 10 guage barrel with a 12 guage diameter bore in it. It really depends on how they make the barrels. It could be that the 12 and the 10 use the same bar stock to begin with, then again maybe not. Or they might use some sort of tube rather than bar stock. It would be as simple as telling the machine to mill the outside dimension of the barrel the same as a 10 guage instead of a 12 guage. If they used the same bar stock it would be quite the waste of metal though.

If I could get a hold of a parts catalog I could tell you for sure. If the hand gaurds are the same for a 10 guage rifled barrel, and a 12 guage ultra barrel you could pretty much bet they were the same barrel with a different bore. I showed my ultra to a buddy and he immediately thought it was a 10 gauge before he looked at the hole in the barrel and I told him it was a heavy 12. I have really not seen that many 10 gauges to know by looking at one to be honest. I would have to go to the local gun store and see if they had any 10 gauges in stock. I don't think they do.

What I can tell by looking at H&Rs website is that the the 12, 20, 410 and so on regular barrels both shot and slug use a SB1 receiver and the 10 guage uses a SB2 reciever. When you look at the Ultra Slug guns the 12 guage uses the SB2 reciever and the 20 uses the smaller the SB1. Except oddly enough when you move to the Ultra Deluxe both the 20 and the 12 use the SB2 reciever. However I can't see them using a different barrel than the regular ultra does.

Bottom line is they are BIG and heavy. If I had it to over again I would get the 20 gauge in the non deluxe model just for more interchangability. From what I can tell none of the shot gun recievers will accept a rifle barrel, so that is out from the get go.

Paul