I have a .270 and would use that, but if you think that's too light weight, have you considered a .270WSM? Some like the .30 cal stuff, but the higher BC and retained energy of the .270WSM makes it a fine round out to 700-800yards. Otherwise if you want easily available off the shelf ammo I'd...
I shot 3 position with an Anschutz 1913 when I was younger. 28" long x 15/16" diameter barrel made it around 15lbs or so. Benchrest at 200yards put 10 rds inside a golf ball. The first time we went out west Prairie Dog hunting we took it along. When the barrels on the high power got too hot...