I imagine that your going to do alot of shooting with this gun, and those big mags kick alot, and after a few rounds your shoulder feels like jello and groups go to hell and you will never be able to shoot really good with a gun that beats you up, you also dont need that much power to get out to 800 yards, get your self a good cheap action, a target style stock from richards microfit, order a 30-32" pac-nor barrel chambered in 260rem or 6.5/284, have your gun smith friend true action and fit barrel, and you'll have a gun that you'll be able to shoot very accuratly at what ever range you want to shoot, and it will have more than enough energy for deer at 800, and the best thing is that it will cost under $800
Brian