I tried loading 181 HH for a couple friends 300 RUMs and they did not shoot great in a 1:10. I didn't play with them a whole lot since they're supposed to be insensitive to seating depth, just ran a OCW test with retumbo and had them seated to fit in the mag box. So I would go with one of the lighter ones, maybe the 152.
I did find a load for one of those RUMS with a 185 Berger Classic Hunter and about 100 gr of N570, and it's around 3500 fps
I did find a load for one of those RUMS with a 185 Berger Classic Hunter and about 100 gr of N570, and it's around 3500 fps