Hello Sarg,

Due to the almost parallel shape of the 458, you’ll probably need to fit a different magazine box and alter the feed rails just a little for that conversion.

I re-chambered a Ruger 77 from 7x57 to 7mm Ackley Improved a few years back and the damn thing gave all sorts of feeding woes, no matter how well I polished the feed ramp and rails. Eventually I worked out when the more parallel 7mm Ackley Improved shells (parallel like the 458) were in the magazine, they were quite cocked over toward the centre of the mag box at the front. Subsequently, when pushing the bolt forward in feeding, the cartridge nose was sliding too far across and missing the chamber before the rear of the shell released from the mag. I simply exchanged the original mag box for a one meant for a 300 Win Mag (a parallel cartridge a-la the 458) and that rifle fed like a champion.

Ruger did make the original M77 in 458 so you should have no real dramas with the feed ramp. Just go slow. Colour the feed ramp in with a dark whiteboard marker before you test it each time and you will see exactly where it is binding, polish a little out and try it till it's right.

Cross bolts and an extra recoil lug under the barrel in the fore-end would be highly recommended too

Alex

alexbeer.com