My only experience with Norma MRP was a long time ago. I used it in 300 Weatherby. I used it because that is what Weatherby ammunition used from the Norma manufacture of their ammo. They actually had loading data using it. I was shooting my "normal" load that I shot all the time. It was in the summer. I had just shot 4 shots of an intended 5 shot string when a friend of mine came up to talk to me. I put the gun on safe and talked to him about 10 minutes. After he left I shot the fifth one. The recoil was significantly more. The cartridge had been sitting in the hot chamber. I had to hammer the bolt open because the brass had extruded in to the ejector hole. The Mark V action was fine. But that taught me a lesson on temperature effects. The barrel was not that hot. The load was about 98% of the listed max.
