Re: 300 rum
For what you spent on that rifle, give it a try first. If it will shoot consistently 1/2 to 3/4 MOA at 200yds, you have a winner!!!
I would suggest Retumbo/H1000 for lighter bullets, H50BMG for the heavies. Fed 215M primers. Had success with the Amax but a bit light. The MK are a no brainer and the 240gr does work well. You may however, find better success around the 210gr range of match bullets.
Have it bedded properly, tuned the trigger as light as you can use, mount a good scope with strong bases and have at it.
At LR, wind doping and trigger time is more important then shaving another 1/10 off a 100yd group. Spend the money on shooting.