Thank you sandlapper.

SGJ: I don't understand.
"Winchester Proof Steel" was the name given by Winchester when introduced in 1931 for the Model 21 and in 1932 for the Model 12.
Ned Schwing states it was 4140.
Winchester catalogs in the 70s state Proof Steel was “cold forged Chrome Molybdenum”.
Certainly within a pour there can be slight variation in composition, but 4140...is 4140.
Have you read that Winchester at some point changed to a different steel?

Craig: there is a ring bulge. The defects I'm calling dents look like 2 annular furrows and are OUTWARD from the bore into the wall, but don't show on the external surface of the barrel; which does show what looks like brass hammer marks as if someone tried to pound down the bulge. I can't be sure that the pin of the wall thickness gauge is in the bottom of the furrow in order to accurately measure the wall thickness, but it is obviously less that the barrel just proximal and distal to the defects. The crack is perpendicular to the furrows however.
I'm only guessing that maybe what started all this was an inward dent that someone tried to raise, which caused the inside annular "dents" and bulge. Work hardening is a good thought.