Well, in a nutshell - - -
- - It's just a heckuva lot of
FUN.
If you must have practicality, then, no, not a lot of that.
But a great many shooters enjoy the idea of having a rifle/pistol/shotgun of a certain type - - The sort that the cowboys carried on the trail drive, the buffalo hunters used, the professional hunters used, the soldiers of various nations used - - -
Most of us could get along with, what, two or three rifles? Four or five? A .22 and a deer rifle. Maybe a varmint rifle and a dedicated match rifle. Many of us have a few others just because we like to have 'em to shoot. I think of a big bore rifle as its own justification. You have something that not every guy at the range has. You can make loud noises and punch big holes in the target. Explode milk jugs fulla colored water for the camera and the delight of your firends. Heck,
just because you CAN!
You might be hard-put to find lighter FACTORY loads for the .458, but there's probably at least one person at every good-sized gun club who loads for this rifle. You might well work something out with him/her.
There are a lot more .458s out there than .416s - - Perhaps more than .375 H&Hs. Used dies can be found at a lot of gun shows. New ones can be bought for a decent price - -Less than the cost of those for some of the big black powder cartridges used in BPCR matches.
For that matter, used .45-70 dies are frequently available, and you CAN use them to neck size .458 brass, expand slightly, and seat bullets. Oh, yeah - -Bullets. The .458" bullets are plentiful, both cast and jacketed, and in an assortment of weights: 300, 350, 400, 405, 500, and 510, I think of right off hand You can load the .458 for pretty much whatever level you wish.
Unless you get into casting, .416 bullets and especially, loaded ammo, are quite expensive. I revently passed on a GREAT bargain in a Remington Safari .416, just because I'd end up spending nearly the price of the rifle for dies, cases, and 300 bullets.
Asto the .416 - -The Remington round is by far the most populer in the USA - -Standard belted case and all - -Far easier to find brass than for the Rigby round. Bullets avilable are 350 and 400 gr. jacketed, and RCBS sells a mould for a 350 gr. FP gas check bullet. Full power loads at (I think) 2400 fps develop more recoil than the 500 and 510 .458 loads.
Clearly, I have no stake in talking anyone out of a .416, or into a .458. Either one is adequate for anything that walks. I just think there is more FUN to be had with the .458, for a more reasonable price, especially since that CZ550 (NEAT rifle, BTW) is available.
And, just think - - - if a local circus elephant ever goes rogue in your area . . . .
Best,
Johnny