Just to muddy your waters....Why a .458 when the .450 Bushmaster is legal...? The .458 is soooooo expensive to shoot. Factory ammo for the BM can be had for less than $30.00 a box...if you are wanting to shoot 600 grain bullets the .458 is for you. 20" .450 uppers can be had for $550.00 and are incredibly accurate with the 250 grain FTX bullets. PS my brother sold his .458 RR and bought a .450 BM..nothing but problems.
point me to the uppers for that price. The ones I found were at the same price as .458 uppers.