Have you actually shot a .458 Win Mag rifle ?
If you haven't, I would respectfully suggest you do so - a bareback one (w/o scope, etc) - to get a "feel" for it.

You may find your dream turning into a nightmare.
One of the lighter factory magnum rifle experiments was the laminated-stock, Remington 600 in .350 Rem Mag (which has no where near the recoil of a .458) that was first upgraded to the heavier Model 660, then discontinued until re-introduced as the Model 673.
It kicked the snot out of just about everyone who tried one - leaving only the determined and guides who needed bear protection to actually keep theirs.
Inexpensive/light/synthetic does not work with hard recoiling cartridges, so be prepared to spend major $$$ on a top-quality synthetic stock, for starters.
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