DM, The gunsmith said that shotguns, and my combo gun, were not designed for the high pressures of larger rifle cartridges. He mentioned that rifle pressures of a 30-30 would be at least double that of a 20 gauge shotgun. He added that the extractors would also have to be changed. He was an older guy, and seemed knowledgeable, but what do I know--I'm a newbie.
My 22 mag/20 gauge IZH-94 Sever has the shotgun barrel on the bottom, which would seem stronger placement for a 30-30 insert. My gun appears very tight and up to the task, but lacking knowledge I don't want to take chances. I was looking forward to getting that insert.