Caliber selection 6.5 vs 7mm Rem Mag

7mm Rem mag has downsides but is really nice in its way. The belted case ends up making for shorter than necessary case life and other minor hassles. It's also got a huge appetite for powder. I shoot a couple of them. < 100 rounds per pound of powder starts stacking up pretty quick. Something like a .284win would give you the 7mm bullet, plenty of case capacity and decent barrel life. A 6.5x284 takes from barrel life quite a bit but pumps velocities way up and long 6.5's have pretty huge BC's. I'd also factor in recoil. Heavier bullets is more kick and there's no attenuating recoil from bullet mass. Only from powder mass. You can get a 6.5CM to 1500 supersonic but that's going to be pretty close to the limit especially in dense air. Since you're building, I'd think more .284win. You can take a 7mag to 2k with the right bullet and load but that might be just a little more snot than you need and 7mag will have no better barrel life than a 6.5x.284.