I had tim help me a bit on loading 500gr hornady into my handi (it has a short throat, can't seat the real long bullets to the correct length). I ended up putting the bullets just a half turn of the seating die deeper than what I needed to- to get the rifle/action to snap shut without difficulty. what that is from rifle to rifle I do NOT know. I'd go measure some but I shot them all up. I used 40grs varget and the brass was good, the primers looked slightly flattened though. Recoil isn't too bad. I used starline brass and only use starline on my "creative" endeavors like that. Ask tim/quick for his varget loads on the heavy bullets.
The other one I use is the sierra 300gr hp (the only sierra .458) w/ 60-61grs of varget. that load is disgustingly painful without modifying the gun. Unlike the one above, this one is published widely (59-63grs varget), though different sources debate whether it's a level two or three load. I've never seen any signs of abuse in brass used five times in my gun.
I packed a sock into my stock, then used a big spoon to cram birdshot into it, let it sit and settle overnight, tried it again and then twisted the excess sock length, zip-tied it, coiled it up, and put the buttpad back on (it ended up being 3 1/2 pounds of lead). I use a limbsaver over that when I'm shooting off a bench but it doesn't work standing/hunting when taking hasty shots, so you're probably better off just using the sock/zip-tie/birdshot. also I screwed a cheek-riser into the stock and glued it down and sanded a nice index spot into it for my cheekbone. if I'm not right on (my index or "hold") then I can't see the sight, works for me. It totally throws off the feel of the rifle but once you get used to it you'll be alright. It's way better than getting that feeling in your face like you got punched in the jaw!