What other people have said about the .458 not quite delivering what it was supposed to (ballistics on a par with the .470/.465/.450 Nitro cartridges) is true. Winchester, for some reason, decided to introduce it as a "short" magnum, counting on ammo sales for rifles in this caliber built on other "standard" length actions. So they had to compress a lot of powder into the small case, which occasionally caused ignition problems. Downloading it solved ignition, but then, it no longer matched the .470-class cartridges it was supposed to. Jack Lott designed the longer 458 Lott to address the .458 Win Mag's shortcomings, and still, thanks to the taper and throating, allow use of standard .458 Win ammo in an emergency. (Not recommend for steady use - chance of chamber erosion and lower velocity.)
The .458 Lott is what the .458 Win
should have been, as the M70 action easily accomodates it. (BTW, I've heard that Winchester M70's in .458 Lott are now available from the factory on special order.)
Some efforts to get the .458 Win up off its knees have involved handloading lighter 465 grain bullets from A-Square to higher velocity. (Of course, the last I heard was that the owner of A-Square was suspended from Safari Club International for ripping off customers, but that's another story.) Speer has introduced a 500 grain tungsten core solid that is shorter than other solids, leaving room for more powder in the case. Handloads with THESE rather expensive premium bullets CAN allow the .458 Win to deliver on its original promise of .470 class ballistics.
As far as the current downloaded .458 not being "enough" . . . I've seen a lot of articles lately about hotrodded .45/70 lever guns being used successfully on everything short of elephant and rhino. It's hard to believe a .45/70 is fine but a downloaded .458 is COMPLETELY worthless . . . but if I were going after big stuff with a .458, I'd still be sure to handload it to its full potential.
The .416 Rigby was designed to out a 400 grain bullet at about 2400. Pressures were deliberately kept low, as the cordite it was originally loaded with was temperature sensitive - pressures went up sharply as the temperature of the ammo increased. With modern powders, the Rigby can approach .416 Weatherby ballistics. (Weatherby based his .460 and .378 on a Rigby case, to which he added a belt.) But as already mentioned, recoil becomes fierce, and you need a BIG action to properly take a .416 Rigby.
The .416 Remington will safely deliver a 400 grain bullet at the Rigby's original 2400, with sane pressures in a Remington M700 or Winchester M70 action.
How much power is enough for the biggest game? First, ignore Karamojo Bell - today, you will NOT have the chance to practice your technique on thousands of head of African game over a period of years. These days, if you place a proper bullet carefully, anything from the .375 H&H on up will do.
I've spoken to a lot of people with lots of experience, and that's the consensus. I've also taken African plains game, lion, and a couple of Cape buffalo with a .375, and it worked just fine. (Of course, since it's only a realatively short list of big stuff, it may just mean I have enough experience to be dangerous!
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