210 Berger, 208 Amax, 200 AB, 240 SMK, or, with the best BC, 230g Berger. I think the weight of the 230 Berger is best suited to that chambering. As soon as I use up my 210 Berger's, the 230 Berger is the bullet I'll be shooting from the 300RUM. Retumbo is probably the best Hodgdon Extreme powder for the 210-240g bullets in that chambering. Even with the 240g, I couldn't get enough H50BMG in the case for decent velocity. H869 will likely give you the best velocity, but it is fairly temp sensitive, much more than the Extreme powders.
Have seen some good hunting results with the 230g Berger on this site. Does anyone have any on-game experieicne/evidence for the 215g Target Berger?