There is a "tolerance" in chambers. If that particular chamber was cut with a well worn chamber reamer, just before they replaced it, it could be just barely in tolerance.
If it were mine, I would contact RRA and ask if they would be willing to re-cut the chamber. (But don't tell them you reload)
The other alternative is a small base resizing die. That's the less expensive short term fix, but it may shorten brass life in your other rifles.