Well the .458 uses a 500 gr. bullet and yours is a 300. REALLY big difference unless you are shooting at little things that don't turn around and try to eat/stomp you.
Build a proper .458 like .458 Win did to do it right.
Do you actualy think that a 300 grainload producing 4700 FPE is equal to a 500 grain bullet producing the same 4700 FPE? Another great example of the uselessness FPE as an indicator of terminal performance
When I got home I ran the numbers to see what kind of power I could expect from 400 grain and 500 grain bullets in the 2.85 COL .45-90. It came up with up to 4600 ft-lbs is possible for the 400 and up to 3800 ft-lbs for the 500. Clearly the comparatively short COL of the .45-90 causes the energy to actually decrease with the longer bullets due to the lower powder capacity.
A possibility if more power is desired, is to hand chamber each round essentially making a single shot rifle. The limiting factor then would be the the length at which the bullet contact the throat. Also, a flat head screw driver would likely be needed to eject an unfired round.
-JR
