Lot of ifs here.

The bores are larger than 12 gauge, and may have been honed, any pitting?
.027 minimum wall thickness isn't bad, but you're talking nitro shells.
.016 is bad, although the location could be a lot worse.

Sounds like a nice gun, I wouldn't risk it. Might shoot black powder loads in it though.

Once you get used to cleaning it not such bad stuff.