You`re bumping the shoulder back, but doing nothing to the case body..resizing it..You stated the fired cases were becoming progressively harder to chamber after each firing, resize the entire case. Pee on the shoulder bump only...I tried that with my 7 Wby mag...after a few firing, had the same problem as you. FL sizing did not change the accuracy of my load..but it sure fed smoother. You can still set up the FL sizing die to head space off the shoulder, if you want.
If your running that case to full bore, remember the pressure your dealing with.
