You are experiencing the same thing I have with Retumbo. It is accurate but spikes on some shots if you run it close to max resulting in the hard bolt lift and pressure sign. That said I think you are high on the pressure charge with the low volume case of RWS brass. I usually have to drop 3 full grains when going from WW , RP or Lapua brass in to RWS. So here is what I would do. Either change your load over to brass with a larger case volume and see what ya get. Or try H-1000 for powder and work a load back up. I would start that load at 72 gr with a 210 gr bullet. Also the ammount you dropped your charge from 77.5 down to 77.1 is not enough. If you see pressure signs you need to back off 3 gr and slowly work back up in 1/2 gr steps.
I shoot heavy bullets in all my rifles because I shoot long range in wind and hunt elk with most of them. We take many trophy elk
each year. Below are a couple pics from last season. The larger one is from a 210Berger in my 300 win taken at 643 yards. We like elk DRT and don't want them running to the bottom of a gulch to expire. This is why we use expanding bullets, the heavier the better.