Any rifle chambered by the maker for the 458 Winchester should take the SAAMI pressure from now to doom's day with no problems. If it won't, then it wsn't a good rifle to begin with.

I refuse to use the term "magnum" in the same breath with the 458 Winchester since the term implies a larger than standard case for the type and the 458 has a smaller than standard case for the type. It is really a bolt action cartridge in more ways than just being rimless. I launch my 458's from a bolt action rifle. If I HAD to have a double using this sort of cartridge, I'd go for the 458 Lott and have it regulated for something a tad less than the maximum load, down to around the 458 Winchester's level.