UPDATE:
My apologies for the "false alarm". For the knowledgeable, this was most likely a routine issue. If I didn't provide enough or clearer information at the outset, I apologize.
RCBS small base dies arrived today. Re-tested on of the problem fired cases. Tried to re-chamber, no go. Pressed through the small base dies, chambers just fine. Since I had installed barrels previously from different manufacturer's, including this one, I'd never experienced a "tight" chamber like this one. I guess I can understand the concept of a manufacturer chambering a factory barrel a little loose compared to one chambered by a company with tighter tolerances. Until recently, I don't even know that I knew such variances existed.
One parting question. Once all the offending brass had been run through the small base die, must I continue to use that same small die moving forward with this barrel? Since I realize that the newly small sized brass will fireform to the tighter chamber of the new barrel, would I be wrong in assuming that a non small based die would allow the base to (or size it so) grow to a larger diameter because of the looser tolerance? Would the smaller based brass retain that smaller base diameter if used in a non small based die?
Again, sorry for the false alarm and appreciate all the assistance.