I am contemplating having a Win. 70 in .375 H&H Mag. rebarreled to .458 Win. Mag. I will primarially be using it for heavy cast bullet loads, mostly on hogs and paper.
Kinda like a magnum .45-70 with a built in safety margin.

Any suggestions as to the type of barrel I should have installed. Is there any major advantage to cut rifling with cast? If I go with cut rifling, should I ask for deeper than normal rifling? And, if rifling is cut deeper for cast, would it still be usable occasionally for full bore .458 Win. Mag. jacketed bullets?

Any recommendations as to barrel maker?

Thanks,
Olevern

Wonder if anyone could take a stab at the original questions?

Most factory 458's use 1/12"-1/16" twists and work well with haevy jacketed bullets, but seem to scatter even the hardest cast bullets. Seems to be stripping the lead from the torque of the fast twist. My own tests somewhat comfirm this. With the chance at a new barrel, I would seriously think about either 1/18" or 1/20". Even if you ran hardball though it, I believe that the performance would be more than adequate. Maybe not 1" bench groups, maybe 2.5-3" groups at a 100yds. Still certainly "minute of elephant". I believe that the ease of getting good cast bullet groups would be worth it. BOL

Thanks, Blackhawk, for your addressing the issue at hand.
Let me add:
From the Lyman Cast Bullet Handbook, pg 120, 121:

45-70's
1-20 - Ruger, Marlin

.458WM
1-14 - Ruger, Remmington 700, Winchester 70
1-15 - Mannlicher-Schoenaur
1-16.5 - Browning

.460Weatherby
1-20 - Weatherby

My Ruger #1 does well with the 485 gr. Lymans. I don't shoot paper, not enough fun compared to what unleashing all that power on cans/jugs full of water!

And let me add:

Ruger #1 bore diameter .450 groove diameter .458 or .4585 .

(Therefore .004 groove depth - which works very well for heavy cast boolets!)

Note also the throat of the #1 in .458 is ideally suited for cast, more so than in .45-70.

So, if I got a 1 in 20 barrel with .004" rifling that would stabilize the 400 gn to 535 gn cast bullets?

Any suggestions as to bbl. maker?

I would think it would do the 300 to maybe 400's but from what I've HEARD the .45-70's (#1's/#3's) don't do the REALLY HEAVY boolets well, where the .458 (#1's) do so. (Can't speak for others, just mine.)