You will need a large action bigger than a Rem action you may be able to build it on a Magnum Ruger action that was a 416 Rigby but i believe a Wetherby would be the best commercial action. Otherwise a custom or even an AR30 would work. Another option if you want to use a rem action get a 375RUM and neck it to 458 and shoot a 458 ultra mag it will fit through the Rem action and be alot cheeper to get cases for and also build. I would probably go for a 416 version though but you must get costing of all the components you want to use includidn dies and cases if you loose a 375 ultra case it is nowhere the cost of a dakota case.
I have a CZ 550 Safari magnum in 416 Rigby and I think it's a pretty strong action for a case like your talking about.
It might be for sale if your looking of one, haven't decided if I want to part with it yet though.
If interested email me and we can discuss it.
Click on my name at the side of the post to see my email address.
Wayne aka WAMBO
If you want 460Wby performance, here is one all done. It even has a good brake on it. http://www.gunbroker.com/Auction/Vie...?Item=51570202
If you don't like shiney it would be easy to put a different stock on it.
If it were my decision I would just but a 460Wby DGR right from my jobber all done.
__________________ Build a man a fire and you heat him for a day. Set him on fire and you heat him for life.
Are you planning to use this gun as a "game stopper" in case of a charge? or are you just wanting a cannon?
if its gonna be a defemse weapon then you to look at reliability also , just incase that first round doesen't do the trick.