Look at cz's 550 magnum, it's basically a large mauser action by design (obviously modified some). It can handle up to .505 gibbs easily. Large magnum mauser actions have been available to hunters since the early 20th century, at a much lower price than many double rifles, not to say that many big bore mausers aren't being made for over 10,000$ nowadays...... But that's not the point, the winchester 70 is a good gun, but it's not designed to handle power like the mauser magnum actions. Building a big bore, go with mauser. The bolt action reliability is there, and has been there since bolt actions started being made for africa.
