Re: 300 RUM Issues...
As someone else stated, I don't think you are seeing pressure signs. The markings on the brass seem to be from a poorly machined bolt face, (easily repaired) on all my ultra mags, high pressure is evidenced by a round circle from the ejector imprinted into the case head and notably loose primer pockets when reloading. In my opinion you have a ways to go. If your gun has a long throat, you could need some more powder to over come it. With a factory remington 700 you should be able to load you oal close to 3.670 as a max. This will get you closer to the lands and reduce pressure further allowing for more powder. Have you checked the accuracy of your powder scale?
Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3070/180 NAB @3300/Leupold 6.5-20x50
Remington model 700 338 RUM LH 26" Bartlein 5C #4 Muscle Brake, blueprinted action, sako extractor, jewell trigger, bell and carlson Alaskan stock/Black cera coat/Sightron SIII 8-32x56 moa reticle, external elevation turret
Savage LH 22-250/Sightron 4-16