welcome to TFL
Welcome to TFL!!
First question, do you have a set of dies for your .458 Win Mag?
IF not, get some. I have RCBS and recommend them, though I'm sure Lyman or some others would be fine as well. I don't like Lee dies, personal thing, they work, but I won't recommend them.
As to all those who gave well intentioned advice about neck sizing and crimp, do any of you own /load for the .458 Win or Ruger single shot rifles???
I ask because what is often sound advice for bottle neck cases and repeating rifles may not apply or apply the same way with a shoulderless case in a single shot rifle.
The .458 (and the .45-70) and some other "straight" rifle cases look straight but are actually not straight cylinders, there is a taper from the case mouth to the base, which is several thousandths larger than the mouth. They are "straight" in that there is no case shoulder, not that they are one constant diameter from mouth to case head.
Even if you neck size, periodic full length sizing is needed as the rounds stop wanting to feed into the chamber. You need a little bit of play to ensure proper feeding.
I don't think this applies to the OP's rifle. It's a single shot Ruger No.1, feeding is by hand, there is no magazine to feed from. Also, since there is no magazine holding rounds subject to recoil, a crimp to keep the bullets in place is not needed.
Also based on my hornady manual both use the same bullets diameter, however the outside mouth diameter is .480 for the 45-70 but the 458 is .481. Leading me to believe the brass could be thicker on the 458 at the mouth. Based on variances in brass and dies you might be able to make it work. But again, dependant on your dies.
It is true, there is .001" difference in the case mouth spec. But, in practical terms, its not going to matter. Because the .458 is loaded just like a straight pistol case. Sizing the mouth down an extra .001" is no big deal, because the expander stem will ensure correct inside neck diameter, and add a case mouth flare. And the flare will be removed by proper adjustment of the seating die.
However crimping can help build pressure by delaying the bulets release.
Barring the OP seating lighter bullets out so far as to barely engage the case mouth...
I suggest moderate-to heavy crimp/fast powders to get decent/reliable ignition
Again, reasonable advice, but more applicable to pistol cartridges with slow burning rate powders (2400, H110, W296, etc.) than the .458 Win Mag.
The .458 Win Mag runs on rifle powders. Powders in the medium burn rate range work best. IMR 3031, 4064, 4320, and 4895 are suitable, as are w748 and some others. Slower powders, while ideal for the other big magnum cases, don't perform well in the .458, and anything faster than IMR 4198 should be relegated to reduced loads.
Proper neck tension alone is enough to ensure reliable ignition and full pressure performance. Factory rounds are crimped so that the bullet doesn't get moved back into the case from being battered by recoil in the magazine. With a single shot, this is not a consideration.
Now, with all that being said, I do FL size my .458 brass. There's simply no reason for me not to. There is no shoulder to be "blown forward" on firing or to be "bumped back" during resizing. So the brass is not being "worked" the same way a bottle necked case is. SO sizing is simple, FL all the way in works just fine and has not given me any problems. (do use lube!!!
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I have made some of the 500gr elephant loads, but mostly I use 400gr cast slugs pushed to the speed of 45-90 /.45-120s and while I have pushed the 400gr jacketed to over 2100fps I find the recoil a bit more than fun for casual shooting and more than needed for hunting anything in North America.
And, while I'm on that subject, pay attention to WHAT bullet you are using and what speeds your pushing it to. The Speer 400gr flat nose is built for the .45-70, and the .458 can push it much faster than design intent. Max loads in the .458 can push that bullet to 2400fps which is too fast. I've driven it to 2100fps, and that is too fast. At that speed the bullet expands...violently, almost explosively, acting just like a varmint bullet, literally blowing up on the first solid thing it hits. Not a good choice for game at that speed. The Hornady 350gr RN is constructed differently and will give proper controlled expansion at speeds up to 2200fps, I don't have personal experience with what it will do when driven faster, sorry.
Get a set of dies for your .458 Win. You can do a neck size "work around" using .45-70 dies, adjusted to the .458 length, but I wouldn't bother. Last time I checked, .458 Win dies were "standard" rifle dies and cost the same as all the others, not a custom order thing. Get a set, and you'll have FL size capability or neck size, which ever you choose.
Good luck, and if there's anything else, feel free to ask.
Its a good round, and versatile with proper loads.
Standard primers will light off IMR powder loads just fine, if you're using ball powder magnums will probably be better, and don't hurt anything if you're using IMR powders, either. At least, that is my experience.