Olevern...I have a Springfield high number being rebarrelled for the .458 American right now. I'm getting a 1-20 twist on it.

Before I took this step, I tested all of the available Lyman and RCBS bullets in my 1-20 twist Marlin 45/70 from the 300 grain up to the #462560 and got good accuracy and stability out of them. I'd go either 1-20 or 1-18 and you'll be all right.

The cut rifling is the way to go and I'm using a Douglas on mine.

Be wary of the throating for a cast gun in .458 Win Mag.

The SAAMI spec throats are too long for good cast shooting. I have a .458 Number 1 Ruger right now and it won't shoot cast worth beans unless I seat the bullets way out which is all right for range work but a little unhandy in the woods. The Lyman 462560 bullet is the exception to this and they're hard to find.

So on a rebarrel, send a couple of loaded dummies with the bullet you intend to use and ask your smith to throat it where they'll just engage the lands and you'll be fine./beagle

This is a little more technical, so interpolate this with the previous answers. You're a former benchie, right? Me too, but shooting cast is a different game by far (far more fun if you are NOT a competitor anymore, but have turned your attention more to "research"). BR bullets have THICK jackets and they are terribly light in weight when compared to the weight of the internals, making programs which calculate twists a little tricky to read. These programs calculate twists assuming a very constant specific gravity of material all the way through to the outside diameter of a bullet. They cannot even compute properly with hollow pointed, based bullets! In general using these commercial programs on the net, a cast boolit stability factor of 1.3 is sufficient, and anything approaching 2.0 is going to destroy accuracy. There is an exception to this little rule in practice, and that is when a boolit cannot begin it's spin properly at the throat (freebore + lead-in). If the boolit is not entirely stripped up front, then a little extra spin could possibly help get a realized factor of 1.3 or thereabouts before the boolit leaves the barrel. Here is where long barrels shooting cast are an asset. My personal experience is almost non-existant when it comes to the big boomers shooting cast, but the 45 colt rifle shoots better than I with lead 185 grainers through 100 easy yards. Twist is equal to 26. A great long range shooter on this board shoots circa 800-1000 yards constantly with a 500 grainer (or better). He has repeatedly stated that the 18 twist is required to hit consistently because of the wind currents are so wild on the open plains where he shoots. So, to sum up, 18 twist is your maximum and 26 your minimum. Emphasizing a custom fitted boolit at 405 grains (chose by me for recoil purposes) I would go no more than 20 twist, and limit my ranges to no more than 300 yards in a windy situation with that boolit. The 45 shooters might not agree, but they are not previous bench shooters either. I am assuming a BR hunter class 308W shooting 168's musters the maximum tolerable recoil for you. To me it is about 3 times too much!!!! ... felix

Thanks, Felix,
That makes sense.
My intended usage is for probably a max of 200 yd. for paper and no more than that for shots at live game (mostly wild hogs). I will be using the Lyman 535 gn. cast (Hammerhead type) bullet mostly, but if the twist & throat allows, might occsionally shoot 405 grainers for extended shooting sessions. I am not particularly recoil sensitive, within reason, so that is not an issue. The gun I am replacing with this project was an exception, an incredibly bad custom stock job with far too much drop and a weight (in .458 Win. Mag) of less than ten pounds (actually 9 lbs, 6 ozs) complete with Leupold 1.5X5 Scope and mounts. It was made to look pretty, not to be shot. This time around, I want a heavier barrel and a correctly purportioned stock, express sites (and a qd scope mount) and a finished weight of between eleven and twelve pounds with scope and mounts. Weight is not a real issue as much of my hunting for hogs is in Texas on a friends 8,000 acre ranch and is either from a blind near his deer feeders or stalking short distances after spotting groups of hogs from four wheelers. I am leaning towards a cut rifled barrel and will seek the advice of the barrel maker on twist, but one in twenty sounds right. I believe I will supply the barrel maker with a dummy round with my bullet installed (the 535 gn.) and have him throat it specifically for that. If it shoots the 405's well, so much the better.
Any recommendations for the barrel maker?

Mr Olevern your project sounds interastin'. Couple caveats. Short of a custom reamer I doubt your going to find much in the way of a cast friendly throating going 458. As mentioned their long and chamber clearances go largish too. Cast shooten favors tighter per less rudder room to promote pre-shot alignment. Something utilizing a bullet 2 thou over groove loaded with 2-3 thou of clearance sounds about right.

My idea is to build the gun around the available molds. Your throating length needn't be long but matching that dia with your as cast dia of your molds would be a big plus. You don't really need the 'boiler room' capacity as your going for a heavy 45/70. Less means better ignition for the most part too.

18 twist is as slow as I'd go if your shooten the large target bullets any. They'll stabilize in the 20 but are near the edge. An 18 hurts you in no way too.

Keieger and Mike Rock make nice cut rifled barrels. I do not think any depth over .004 helps as the 45's are normally 8 groove. A 6 groove holds 30 cal find even at top speeds shooten cast... just have the bullet big enough dia. I used to think the cut rifled barrels had an advantage but I think all of the top barrel makers do a good job. If anything the button rifled barrels are smoother as made and require less lapping to a nice shooten finish.

Aladin,
I am planning on purchasing a custom reamer, so that the barrel maker can get the throat right for the sample I give him. When he gets through cutting the chamber, as I will pay for the reamer I will have him ship it to me with the rebarreled action. Almost have to go this way if you have ever seen the bullet in question, pretty much nothing else like it out there except the "hammerhead" brand bullets.
Very wide meplat and long bullet.
Thaks all who replied for the opinions and information.

Sounds like a sound plan Olevern. It's going to be interesting to read your firing reports when you get it going.

Vern, check out Skip Talbot and his friends out there in AZ for a possible takeoff barrel. He just might have a few laying around in 45 caliber, or know of others who might have. There is nothing better than a BR barrel already broken in (for lead shooting), that won't hold a 4-6 inch group anymore at 1000 when shooting match condoms. Might be able to get it for postage plus a little beer. There won't be much demand, I don't think. Anyway, Aladin is correct; a good barrel can be had by any maker. The quality of the steel on the microlevel does not have to be as good to shoot lead as for condoms. ... felix