Yes, the bore diameter is nominally a 10 gauge, but it is an overbored 12 gauge barrel, not a 10 gauge barrel, was my point. Back when I was experimenting I found I couldn't get good wad sealing over about .742". "Wasted" 2 barrels in the process. I was not dealing with 3-1/2". I have not heard any bad reports on the Mossbergs, so I wonder if the manufacturers have modified the wads, or if some wads do better than others.
The early 3-1/2" 12 gauge BPSs were built on the 10 gauge receiver, and a guy who had a 12 borrowed my 10 and said the barrels would swap. I don't know if the gun would have functioned or not. I do know that was a heavy 12 gauge if it did.