Do I have a Brass or Chamber problem?

[PJgunner]

Hmmmm! Is that .377" dimension on just one side of the casing? Maybe your chamber is a bit on the large side for the round. A case laying at the bottom of such a chamber would expand more on the unsupported side than the side that was at the bottom of the chamber.
What does bother me is, if that was a custom barrel with custom chamber, I find it unsettling that it would be oversized in it's dimensions.
The fact that you've had that barrel for such a long time probably means you can't get the factory to fix it for free. In fact, it would most likely take a whole new barrel with chamber at the proper dimensions to square that problem away.
Probably the only real problem might be a bit shorter brass life, but with .223 being so plentiful, that wouldn't be much of a problem.
Paul B.