I'd pick a standard length (long?) action for any 30 caliber cartridge burning more powder than a .30-06. They hold epoxy bedding better and won't twist as much from barrel torque than shorter actions. It doesn't matter if they're 10% less stiff than short ones; they bend the same amount for every round fired anyway; repeatability is the foundation of best accuracy.
And one of the modern rimless bottleneck cartridges is a lot easier to load for best accuracy than any belted case. Back when belted cases were winning long range matches setting records along the way, folks got best accuracy with new cases or full length resized fired ones body sized a second time with a special body die swaging down the tiny ridge about .005" in front of the belt left there from the chamber edge causing it at peak pressure. Ordinary full length sizing of fired cases never quite shot as consistantly accurate as these.
And use a Win. 70 action to build it on. They're near 3 times stiffer than Rem 700's.
And one of the modern rimless bottleneck cartridges is a lot easier to load for best accuracy than any belted case. Back when belted cases were winning long range matches setting records along the way, folks got best accuracy with new cases or full length resized fired ones body sized a second time with a special body die swaging down the tiny ridge about .005" in front of the belt left there from the chamber edge causing it at peak pressure. Ordinary full length sizing of fired cases never quite shot as consistantly accurate as these.
And use a Win. 70 action to build it on. They're near 3 times stiffer than Rem 700's.