I had a 416 pieced together and finally got to shoot it the other day!!!!
I bought a take off barrel and stock and had my gun smith put it on a Winchester model 70 classic action that used to be a 7 STW. I feeds fine and once I get it all blued it will look good. I need to do some more bedding to it as there is a gap between the action and the stock on the loading port side I guess the express actions have a slightly different design as the stander ones do?
I used RL-15 and the 400 gr TSX first two load where very slow 2280 and 2330, I will start working up to try and get 2400-2500 out of it.

I do not have a scope on it yet and I thought it was a pussy cat to shoot of the bench till the last round and I did not get it tight against my shoulder and BAM that one hurt a little!
I v shot my buddies 458 lott and it did not seam as bad as this was.

If all goes well in a few years it will get to do its stuff on a cape buffalo or two!

Congrats, welcome to the big bore club. I think you'll find a 400gr anythign a great killer of game even at 2300fps. I run my .404jeffery @ 2250fps w/ a 380grNF & adding 100fps only increases recoil. Be sure to give the NorthFork a try, great bullets.