RE: could there possibly be a problem with a winchester?
I had the same problem with my M. 70 synthetic stainless in 300 WSM. After firing the bolt was very tight and hard to open. With more shots fired it got worse as it heated up. It turned out the lugs were not seating evenly and needed to be lapped. Once this was done the problem disappeared and it now shoots excellent. I'd suggest having it looked at by a Winchester authorized warranty location. Lapping the lugs could increase headspace and this must remain within 3 & 6 thou. (I think). gg.