G'Day Fella's,

I have had some experience with this Most Frustrating of problems!
Magazine feeding problems, is one of the most time consuming and difficult problems to solve.

As Con and 4seventy have stated, the problem is not always the firearm but can be the ammo.
With the firearm, it can be the follower and the feed lips of the magazine box or the profile of the bottom of the action and or feed ramp. Carefully compare these parts/areas if you can against another, same brand firearm that operates without fault.
If everything appears to be OK with these, then look at your ammo for a solution.
The non-bottle necked .458 Win Mag cartridge itself, may actually be the problem?

Sorry, I can't be of much more assistance to you than that.

HooRoo
From
Homer