Is the .358 STA a straight clean-up on a .300 Weatherby chamber ??

Thinking of re-boring and re-purposing a 70 Classic.

I’d bet a quick search of chamber drawings would tell you, but I believe so. If not, lopping a thread would do it to I’d bet.

I think the barrel would need to be set back at thread or 2 to clean up the Weatherby radius shoulder

I’d be a bit more concerned with your magazine length. The 8mm Rem Mag converted to 358 STA has a COAL of 3.65”, the 300 Wby is shorter at 3.56”. For a long distance powerhouse, I’d be more interested in a 338 RUM, which already has a shorter cartridge length by 0.05” at 3.6”. .33 caliber bullet technology is far more abundant than .35 caliber and the .33 has more variable weights for use, which makes it far more adaptable to any game situation.

It will be next to impossible to find 8mm Rem Mag Brass, therefore you’ll need to find 416 Rem Mag Brass to neck down or screw around with deriving from a long 375 H&H variant.

The 338 Rum is easily formed by necking up available 300 RUM brass and trimmed to its shortened length at 2.76” in lieu of the 300 RUM at 2.845”.

Just a thought.

I'd do 338 Laupa long before a 338 ultra mag.

In my experience .358 caliber is a bigger Hammer than a .338

Lapua is a great one, but he’d need a whole new setup to accommodate that chamber. I’m not talking about just the “hammer” side of it when comparing to the .35. With the 338 RUM you can cover two sides extremely well. .33 bullets hit a sweet spot not unlike the .26 and .28 cals. That means the .33 will achieve better ballistics all the way down the line with excellent BC and SD, especially operating at 338 RUM velocities.

It’s all about what you hunt and how versatile your needs have to be with a particular rifle.

Just a suggestion to the OP.

Or just run the neck up to 340 Weatherby. The 358 STA should clean up the Wby chamber. GD

Thanks for all the info and insights, fellers.

This whole thought of mine is more of an "I always just wanted one" whim rather than a "I really need a big, long-distance hammer" thing. Just always been intrigued and I've got enough other .300 Mags that this Model 70 could be done without as a .300 Wby. I've got a 26" barreled .375 Roy........it's all the long-range hammer I'll ever need. I guess, maybe I need to put the horse first instead of the cart and see if JES would even do an STA. they don't list it as a chambering. AND measure the mag box.

I bet he will do it, you just might have to pay to rent the reamer. He did my 35 Newton for me. Turned out nice.

I totally understand just wanting something and for 250 bucks it's hard to go wrong.

This is what I was thinking. Can rent the reamer for $50.

Yeah, he is pretty reasonable. I like to send him a few dummies as well, just so he can check the chamber and maybe a couple he can load and shoot, just to verify everything is good. Worth it these days with the cost of shipping.

IME the 358 STA is a lighter 375H&H or 375 Ruger analogue useful for similar game. The 338 RUM and Lapua seem better suited to long range shooting and hunting.

I may be in the minority but I don’t see the 338s and the heavy 358s (Norma and STA) as comparable cartridges in practical use. Loonies can make a theoretical case based on paper stats but the application of the cartridges and the type of rifles built for them, in the field, are very different IMO.

Not sure where you’re at with your .358 STA idea, but I have some new Remington 8mm Mag brass I’d sell ya if you need some.

Doc_Holidude