Home Forums Hunting & Shooting Express Rifles and Big Bores Only Winchester 70 458 build

I've got a New Haven late 90's standard long action and a Brown stock "sitting around." Was gonna build another Whelen but I dunno. Haven't been supporting the economy enough.

So: apologies for the dumb question.

Aside from getting the bolt face opened up (by whomever does the barrel install), swapping out the extractor for a magnum extractor (which I have), and putting a 458 follower and mag box in, can I build a 458 on this thing? Are the factory 458 actions machined any differently from the standard long actions?

Might be the berries to have a stainless 458 for my occasional Alaska jaunts. Even if I killed my last caribou with a 7-08...

And for a final maybe dumb question, I sort of prefer 24" barrels to shorter ones. But is a 24" 458 gaining much over a 22"

Thanks in advance.

Edit: Just realized I have a 375 HH mag box/ejector/bolt stop off another project. Maybe a 458 with a longer box?

Should be fine. I used a Wiebe floorplate on my conversion of a New Haven Classic from 270 to 375H&H Belted Mag. Williams magnum extractor. Works great, modified Legend stock.

The 458 would be perfect, wish I hadn't sold mine.

The longer box would be a good thing, allowing the seating of long bullets longer. As to a 22" vs a 24": some velocity is lost, obviously, but how much would depend on how it would be loaded, if handloaded. I've owned a 77 Ruger in .458 with a 22", but the action was also shorter making it kinda compact for a .458. The CZ 550 in .458 I owned for a few years was taken on a moose hunt which meant some trekking through alder patches, but I didn't really notice the extra 3-inches of barrel. I doubt that the extra 2-inches of a 24" tube would ruin your day. My current Ruger #1 has a 24" but without a magazine as a single shot it is quite compact, though as heavy as the CZ 550. That extra weight is in the barrel that helps tame recoil jump.

Bob
www.bigbores.ca

This is excellent. I prefer the 24" anyway. What are you guys running for barrel contours?

24 on my whitworth and guessing number 4 sporter is about what those factory barrels are. It’s a perfect hunting gun size and weight for a 458 wm. Light for bench work but I’m a hunter.

Bucking for Kighthood in the .458 Winchester Magnum Brotherhood, eh ?

You will probably gain 40-50 fps with the 24" over the 22" barrel length,
with most loads, whatever the bullet and powder used.



The original Pre-'64 .458 WinMag was done on a .30-06-length action with no-opening-up fore or aft,
just bolt face and magazine-rails-ramp feed job, the M70 African:



They had to open up the Pre-'64 forward and aft for the H&H-length .300 and .375 cartridges,
mostly rearward but receiver cuts for ejection and loading clearance were done on front ring too.
By comparing the MRC-X2-M1999 in 26 Nosler to a factory Pre-'64 H&H action you will see how Winchester opened the .30-06-length action.
Photos below I did previously, thinking of turning the MRC into a .458 WM+ 3.6",
decided the SAAMI .458 WM 3.34" would be plenty for that MRC:







Your M70 Classic .30-06-length action is same length as .375 H&H-length, but has magazine blocked at back, rear bridge is longer (forward),
and so is the ejector-bolt-stop so ejection occurs sooner as bolt is drawn rearward, and bolt stops sooner at .30-06 instead of .375 H&H ejection position.
The Classics and current FN/SC/Portuguese-assembled M70s in .458 WinMag have the rear bridge opened rearward,
Same rear scope base hole spacing as on the .375 H&H: 0.330" rear, 0.850" front
(Pre'-64 .458 WM had 0.850" fore and aft, Pre-'64 H&H had 0.425" or 0.437" rear and 0.850" front hole spacing).
The latest M70 .458 WM has magazine block at rear and longer ejector-bolt-stop.
Scope base hole spacing is 0.330" rear and 0.850" front.
This would be an easy conversion to .458 WM+ for 3.6" COL:



This is unlike the latest .338 WinMag M70, same action except with rear bridge extending farther forward,
thus shorter ejection port, greater length between rear scope base holes, same front receiver ring configuration, etc.
0.850" center-to-center on both front and rear scope base holes.
Latest M70 .338 WinMag below:



Now for the 1990's Classic with same basic receiver configuration as the latest .338 WinMag M70 Extreme Weather:



Immediately above is a Classic M70 .270 WCF that I put a 3.6" mag box in and shortened the ejector-bolt -stop.
It ejects 3.6" COL just fine, currently as a .400 Whelen-B with skinny No. 4 sporter, 25" barrel.
No cutting or milling on receiver bridge or ring was required.

No. 5 sporter contour , 24" length and 1:14" twist is happiest for a .458 WinMag.
Do a No. 4 for a featherweight but then you need to shorten it to get muzzle diameter thick enough.

You gain less for each inch above 24" than you will lose for each inch under 24".
24" is some sort of inflection point.
Light bullets and slow powders lose more per inch than heavy bullets and fast powders.
But it is a wash, since we usually use faster powders with lighter bullets
and slower powders with heavier bullets.
About 20 fps loss for an inch of shortening below 24", and about 15 fps gain for an inch above 24" length.

And as always, Sir Ron has the whole story complete with pictures. A living book on the 458 WM. Thank you Sir!!

Sir Dennis,
Buy a donkey for those flowers.

I will take some new pictures showing the Connecticut Winchester M70 Classics side by side.
1) the .270 WCF converted to 3.6" COL .400 Whelen-B with just a longer box and shortening of the ejector-bolt-stop, and re-barreling.
2) the .416 RemMag converted to 3.6" COL .458 WinMag with just a re-barrel.
Both work, will eject unfired 3.6" COL cartridges.
No cutting or milling on the receiver required.

Same has been done in past with converting a Ruger M77 Mk II to .375 H&H by putting RSM sheetmetal box into it,
and shortening the ejector-bolt-stop. The Ruger gunsmith did that for Dave Scovill,
who sold the rifle to Phil Shoemaker.

Old picture of the .416 RemMag M70 Classic converted to .458 WM+:
It has a 23"-long No.4 sporter McGowen barrel and weighs ~ 8 pounds bare/empty.
If using a 24"-long No. 5 sporter McGowen barrel, ~ 8.5 pounds bare/empty is in the ball park.





Side-by-side photo comparison of the .270 WCF and .416 RemMag M70 Classic actions
after I get back from a weekend of muzzleloader deer hunting.
Bleep Joe Biden.

Guess I'm joining the Brotherhood. Thank you, Sir Ron. This is unbelievably helpful.

I will think on the barrel contour. My 375 was 10 lbs scoped and it was a bit too heavy. But maybe that's a good weight for a 458.

I'd always heard that you couldn't get a loaded 375 round to eject from an M70 1990's + long action action with a standard rear bridge, but had no personal experience with it, so it's interesting to hear that 3.60 COAL cartridges will work.

This thread really makes me appreciate what we had in Winchester 'back in the day'.

The .270 WCF M70 Classic converted to .458 WM+ sure would be an aesthetic pleaser.
The greater hole spacing on the rear scope base, and the longer length of bridge looks stronger,
whether significant or not.

I have a fallow stainless M70 .30-06 that needs the treatment of conversion to .458 WM+.
That would be a good use for my one remaining Duane Wiebe XRM mag box (4+1 instead of 3+1 with factory box)
and my one remaining Jim Wisner copy of the African rear sight.
I'll be needing an NECG front sight,
and a McGowen No. 5 sporter of 1:14" twist for that.
I'd make it 24" for barrel length.
Expect that to total about 8.5 pounds in a synthetic stock.

Some thoughts on the lightest barrel to be considered, No. 4 Sporter.
If I did another one on an M70 30-06 action, I would use a No. 5.

This is great. All very useful to see. The thinness of the #4 barrel wall is surprising--I can see the need for the no 5.

I switched the bolt from the .458 WM+ M70 Classic into the .270 WCF M70 Classic that has 3.6" box, shortened ejector, and .400 WB chamber.
The XRM box allowed 4 down and closing of the bolt.
I used four .458 WM+ dummies at 3.57" COL.
The .400 WB chamber is big enough for the .458 bulleted dummies to start into it.
The rails retained and the dummies fed.
The rifle ejected them with room to spare as the bullet tips swing by the right side of receiver ring.
This is with the action having the long rear bridge.
There is no impediment to thumbing cartridges into the magazine either.
Start either the rear or forward end of the cartridge into the action and it just falls into the magazine.

Having known for years that all my unaltered .458 WinMags on the .30-06-length actions will eject unfired cartridges up to 3.54"
I never even thought about using a .30-06-length action with shortened ejector-bolt-stop and lengthened box
for a .458 WM+ and 3.6" COL.
DOH !

This concept is going to get some use.
Why weaken an M70 Classic Connecticut or FN-made .30-06 rear bridge to .375 H&H rear bridge ?

I'd say that's about the most informative writeup I've seen here or anyplace else.

that is super cool!!!!!!!!!!!!!!!!! long live 458!!!!!!!!!!!!!!!!!!

Ron - thanks for the detailed explanation of the XRM box and M70 mods.

Do you need a different follower and stronger spring in the XRM box ?

Could you possibly take measurements of the XRM box and follower and compare with the stock M70 parts?

I might have to resort to making one locally as these sorts of parts seem impossible to source.

Sir Joe,

Stay tuned. I will dig out the one remaining XRM box that I have for use in my .30-06/.458 WM+.
Will apply mensuration instruments and make a little drawing with dimensions labeled.
Last I heard Duane Wiebe was not selling those things anymore.
I did get a follower to go with it from him too.
It was massive like the one he supplied with his .500 Jeffery bottom metal on the other thread.
Might have been a mixup.
I ended up using a regular M70 Classic follower in mine, same spring too.

I’d love to get one of those Wiebe boxes for my .416 Taylor.