My husband would like to build a 458 that betters the ballistics of the 458 Win Mag but keeps approx the same case length. He's been interested in something on the order of the 450 Howell or the 460 G&A MAG. However, the 404 Jeffery case that both these rounds are based on doesn't leave much shoulder when necked up to 458. He likes the cases without a belt but he'd just as soon not have something that may be a little marginal on head spacing because of a skinny shoulder.

He says there are a few non-belted cases that are fatter than the 404 Jeffery: the 450 Dakota and the 338 Lapua to name a couple. Both of these are of the approx diameter of the old 416 Rigby at the base and would have more than adequate shoulder when necked up to 458. The only problem with them is that head size is too large to fit the Rem 700 that he intends to use. (This is the rifle I bought for him several years ago and he hasn't shot anything through it yet because he's been planning on wildcatting it! ) So his question is this; does anyone have any experience at turning down the head on any of these larger cases to 532 dia and cutting the extractor grove deeper to match? Do either of these cases or any other case of the size mentioned have enough brass in the head area to support doing this?

I've heard of feeding troubles with rebated case rims and the 700. And much less rebate. I guess the RUM's are working fine (.546" - .532") but to go from around .590" all the way down to .532" is a long stretch.
The bolt has to be able to catch the rim to push it forward, so the round has to come up out of the box enough to catch the boltface, but getting it to do that without the round just popping up out of the action would be a trick.
I'd completely and utterly abondon the idea.
Either get a different action or go with the 404J.
Don't worry about the shoulder, since the G&A has shown no signs of headspacing trouble.
I think it's a fine looking round myself.
Does your husband type?
Bring him over some time.

The usual manner of adapting a Rem 700 to accept .416 Rigby/338 Lapua cases is to open the bolt up and install a Sako type extractor. I know of several rifles that have shot a lot of rounds of .338-416 Imp. and .338 Lap Imp. and are working fine. All are setup as single shots, period.
However, a number of known, bright people have cautioned against going to the big case on Remington actions. Folks like Lilja, Tooley, Borden and others say not to do it. I don't know of any actions that have failed in service but many have stated that you will see lug abutment set-back, eventually. I have not observed that in my friend's Remingtons. And I would also not build one of these. BATs and Nesikas are great, new actions to start with. Hunters may choose the big VZ actions or 1917 Enfield for an action. Opinions by Jay

sell the remington
buy a cz in 416 rigby
rebarrel to 450 rigby

jeffe