Busy under those tubes.

Has the mark for reproof, and, as noted, was standard bore for 12 gauge at that time, prior, it was 13 bore.

If it were mine, I’d spend a good amount of time measuring wall thickness. Maybe it passed proof with .019 wall thickness, but, I’m a klutz, and would want a bit more than that.

I wouldn’t buy a gun at less than .025 wall. Anyone else can do whatever they want.

Best,
Ted