300 rum
I shoot a 300 RUM, there are alot of reasons not to suggest a 300 RUM, the biggest seems to be not being able to get good brass. Nosler custom brass is available again here and there, it's not too bad but it's expensive. The throat in this gun isn't wearing much since I dropped velocities to 2900, but anything above that and every 50 rounds you can measure it moving out. Unless I'm really missing something I can't get the case capacity where I think it should be. I did just add a muzzle brake to help manage recoil, it's in a light gun(I was the guy with the duct tape on his finger at Pella).
I'm planning to test bringing the velocities and pressure up to the max to see if there's an accuracy improvement and shoot up this barrel. After that test I'll likely recamber but that will take some time to sort out.
I'm a rookie at this 1000 yard stuff, and there's a big learning curve so keep that in mind but I wouldn't suggest going with a 300 RUM. This barrel has over 750 rounds thru it and unless I'm going to use it as a hunting gun I'll switch to something else when it's gone. I'll have 2 new 30 WSM's for next year regardless.
(H1000, 210 Bergers, 208 Amax's, provide the best results I've been able to acheive with a 10 twist. If I were going to keep this around I'd setup for a heavier bullet and change twists.)
Good Luck!