I just loaded 40 rounds for my 300 WSM. I didn't lube the inside of any of them for whatever reason, and didn't have the same results. I had about 12 of them that were nickel and the rest were brass cases. They have all been shot from the same gun and each and every nickel one was hard to chamber while the brass ones went in like butter. Does nickel "stretch" more than brass? Maybe if I had lubed the nickel ones they wouldn't have been hard to chamber?
Hmmmmm, maybe I should try that next time. Very interesting.