Re: Baffled ??? - UPDATE
For those of you who are interested, I have finally identified the problem. Apparently the problem was caused by the priming arm/post in my press. Although nothing was broken it did show some wear. A call to RCBS is all it took to get a new assembly shipped out (priming arm - sm & lg post - cups - spring)
I installed the new priming assembly and primed up 20 338 RUM cases. Priming was easier, smoother and every single primer was sitting a few thousandths below the case head.
What an odd problem to develop after so many years of trouble free service from my RockChucker press.
Considering that the press has been in service for nearly 35 years I would have been happy to pay for the parts but they wouldn't take a nickle and shipped everything for free. SPECIAL THANKS to RCBS for the fast, courteous service.