Re: 300 RUM Issues...
I ran your numbers and your calculations seem correct. I came up with 12.75 moa @ 700 and 20moa @ 900 using 2860 and a 231 yard Zero which exbal says is 2 inches high at 100. Can you seat your bullets a little longer and still fit the magazine? By extending the bullet, you create more case capacity and thus reduce pressure, so you would have to add more powder. It could be possible that you have a tight barrel. How are your velocities with other bullets?
Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3070/180 NAB @3300
Remington model 700 338 RUM LH 26" Bartlein 5C #4 Muscle Brake, blueprinted action, sako extractor, jewell trigger, bell and carlson Alaskan stock
Savage LH 22-250