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.

Originally Posted by TX35W
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?


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:

[Linked Image]

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:

[Linked Image]

[Linked Image]

[Linked Image]

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:

[Linked Image]

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:

[Linked Image]

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

[Linked Image]

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.

Ron aka "Rip" for Riflecrank Internationale Permanente
NRA Life Benefactor and Beneficiary
.458 Winchester Magnum, Magnanimous in Victory
THE WALKING DEAD does so remind me of Democrap voters. Donkeypox.