Stan,
I've never had any bore pit from rust and I don't run a bore swab sometimes for several seasons. But I also don't hunt the salt marshes.

I beleive those really badly pitted bores in vintage guns I've seen were a result of corrosive primers and/or black powder. I also beleive a gun with hardchrome bores, subjected to those conditions that badly pitted guns of the past, would also suffer similarly.