I believe Savage almost if not all their own barrels.

What specific model 12? There are a lot of 12s.

If its a standard 12 then they make it for that gun. I suspect all. They are button rifled by the way which is one main reason they shoot well even if they do not lap them.

They may lap some of the high end stuff.

I had a chance to see a 5R off one of the McMillon stock guns (forget what model that is)

Same rough interior finish that the other ones are, so nothing special in that regard.