Talley (and other) scope mounts for Winchester Model 70s are divided into a few categories. In Talley’s language, one is “magnum-length” (.300 and .375 H&H) and one is for “standard caliber” (.30-’06 family plus .264/.300/.338 Win Mag… no mention of .458).

The action on my .338 Win Mag seems to be long enough to accommodate the .300/.375 H&H cartridges… but there must be some kind of difference I can’t see.

What’s the deal, please?

-Chris

Rear screw holes spacing, Pre-64 standard .860" and magnum .435″, Post 64 standard .860" and magnum 330″

Found this

Making sense of the pre-64 model 70 receiver

Thanks, Darryle, for that link.

I meant to say originally that I saw the three different screw-hole spacings for the rear sight mount... but couldn't see anything obvious on mine to explain why. Hard to see difference with only the one to look tat.

-Chris

I don't think Winchester has ever made a true magnum action. The really long cartridges like 375 and 300 H&H are on modified long actions. There is more metal machined away from the front action ring to get the extra room in the loading/ejection port. The magazine has to be modified as well. They will take different scope mounts since the spacing on the scope mounting holes are closer together on the front ring.

But I won't swear this is right. It's been a long time since I actually held one in of the H&H magnums and only a couple at that and I could be mis-remembering.

I don't believe the above photo is accurate. The Short Magnums are exactly the same as a short action. The stock and scope mounts from my 308 and 300 WSM were interchangeable. I know I'm not mis-remembering that. The magazine follower and feed lips were different on the WSM. But the action screw spacing is the same as a short action. That is not what the above photo is showing.

For the current post 64 Classic M70 actions, my understanding is that the "long action" and magnum actions" are the same length / foot print. The differences that I am aware of are:

1) Shorter bolt stop and ejector. Allows the bolt to cycle H&H length cartridges further to the rear to clear the front receiver bridge when ejecting loaded cartridges.
2) Magazine box does NOT have the 0.200" spacer welded to the rear of the box to limit COAL to 3.400". Likewise a 0.200" longer magazine follower.
3) The one outward visible difference is that the front of the rear receiver bridge is milled further to the rear. Hence the shorter scope base mounting screw spacing. referenced in the OP.

It is possible to convert a standard long action (eg: 7mm Rem mag) to an H&H length cartridge. All that needs to change are the bolt stop, ejector, mag box and follower. While cartridges may occasionally contact the front of the rear receiver bridge during ejection, I did not have any issues as a result for the one rifle that I had converted.

Having said all of that, for the novice, it is a lot simpler to just start off with a rifle that left the factory as an H&H length cartridge. eg: 7 STW or 300 Wby. I had to play with 2 or 3 aftermarket long magnum magazine followers to ensure 100% consistent feeding from the magazine.

Not exactly right, but you already knew that. The picture above is of the pre 64 model 70 receivers. Also, there is more cut out of the receiver than just the front. They also cut out a section of the rear receiver to allow for better loading of the long H&H cartridges. Here's a better picture. You'll also notice the front screw spacing is .860", while the rear screw spacing is closer (.435"):



I also wanted to add that the OP didn't specify whether he's asking about the pre 64 or post 64....

The OP needs to explain exactly which action he has - either PF or CRF... The PF actions in the full-length magnums had different rear bridge hole spacing than the full-length CRF actions... I have examples of both rifles..

Thanks, bsa, those pics really help. Here are pics of mine, for comparison:






Mine's a post-'64 (circa '71) .338 Win Mag, and comparing the two in the photos clarifies that both the forward and rear bridges in yours have been hogged out (?) to accommodate the extra-length H&H rounds... compared to mine, where the top metal runs straight across (athwartships, so to speak, or due east and west maybe) both fore and aft. Well, maybe not as obvious as it would be if I didn't have the mount bases installed, especially the forward base that extends over the back of the forward bridge a bit.

Sorry, all, that I didn't post more info at first. My questions came about as I was progressing through a "swap all the scopes" project on a few rifles at the same time. Mostly just passing time, but it got me gloss scopes on gloss rifles, matte scopes on matte rifles, size/weight/magnification slightly more appropriate to platform, cartridge, expected use, etc...

So here I am, reviewing various rings and mount bases... and I'm reminded there's a difference in hole spacing for the rear bridge mounts. Hmmm... Whyzat? Just as a matter of interest, mostly...

I've "known" sorta-kinda all along that the "long" Model 70s could handle both .30-'06 length and H&H length cartridges... but without having one of each to compare... and without seeing really good pics... and with measurements indicating an H&H cartridge could actually fit in mine (although without knowing whether it would "work" or not)... it just wasn't obvious to me how Winchester solved all that. Very clear, now, and I appreciate the education.

-Chris