The 458 does not have a inherent accuracy like the 308 Win.All I am saying is that its accuracy for consistent 2-3 inch groups, has a curve with a sudden steep drop at ranges beyond 50yds.I base this conclusion from the experience of owning and shooting various 8 458's some of which I rebarreled.
There is a very excellent article by Warren Page in (I believe) the 1970 Gun Digest summarizing all of Remington's data for their 40X, fired for group before selling the rifles. The data proves that smaller calibers are more accurate than larger ones due to less leaping, torquing, and blasting.
So...I would be surprosed that a bunch of .308s were not more accurate than a bunch of .458s. .308s are a bit more accurate than 30-06s and .223s are more accurate than .308s.
So what?
If your .458 experiences a sudden opening of group size in terms of MOA at 50 yards, you may have discovered a new and proprietary law of physics.
