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To the group I'm in the process of trying to put together a Winchester model 70 in 340 Weatherby Magnum. Old crip and I are looking At using his 338 WM donor rifle. I am very confused about receiver sizes at this point in time. I currently own two Winchester Classics one and 300 Remington ultra mag and one and 300 H&H. I previously owned one and 375 H&H. These all are newer post 64 CRF actions. All of these appear to have rather lengthy openings where the cartridges are inserted. In fact Leupold stocks a specific scope mount for this rifle action size that is different than the ones listed for the regular magnums like the 338 wm. Since I have never looked at 338 Winchester Magnum up close I'm confused about whether there is a difference in the magazine well opening on the top of the receiver or not. I been told in a previous post that it is easy to convert at 338 Winchester Magnum over two 340 Weatherby I would just like a comment from somebody who's actually measured the magazine well opening on the top of the rifle to confirm for me that there that no difference between the two. Any help would be great thanks. A picture of the two side by side would be Wonderful. Thanks and Merry Christmas  Brad  | ||
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Brad I thought pretty much we all agreed that the factory M70 375 length port opening was slightly larger than the 338mag length. I don't have one here but either the opening is longer or there is a notch cut on the front of the 375 to help clear a loaded round or maybe both. While I have not use a 338mag to convert to 340 I have used a number of 7mag and converted them to 7 STW. That conversion works fine. You do need to slip the bullet end in first to load the mag. I never had trouble ejecting a loaded rd and an empty would be no issue. Yes a 375 length donor would be easier. A 338mag donor will also work. You can open the port if you want or use it just as it is. Empties would never be an issue. If you have a clearance issue with a loaded round open the mag floor and drop them out. As usual just my $.02 Paul K | |||
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Ramrod I did some checking and I think it is as you point out action length is the same. Rear bridge is shorter on the 375 H&H to accommodate the longer rounds. I think everyone is right on this one. It will work but might need a little adjustment in some circumstances. Hence can be done just easier with the longer one.  | |||
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There is not much to see unless the bolt is pulled back so you can see into the receiver bridge from the front. You can find photos of both on the net very easily. The .375 H&H has rear scope mount holes .335 apart. I think the standard M70s are .760 between holes.
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Well that would explain why my swiss cheese memory can't remember how the port was different. Been too many years since I had them side by side.  Brad for sure the ACTION length is the same. As usual just my $.02 Paul K | |||
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 338 Win Mag  300 RUM pictures worth a thousand words. Thanks Brad  | |||
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Ok, I have done this; post 64 long action M70 receivers are the same overall length. I took a 7 mag and made it into a 338 RUM with no alterations to the receiver. Push feed. True, they cut the bridge back on crfs maybe to get better ejection with the fixed ejector blade. I recommend the RUM instead of the Wby as it has no belt and gives slightly better speed. And fits into a mag bolt face as is. | |||
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Brad Notice the exposure of the tail of the extractor on the two differnt actions. The .375 receiver leaves just enough capture to ensure the extractor does not hang up when the bolt is pulled rearward. I think there is also a small chamfer of the material above the extractor to clear a case when ejected. If I was going to monkey with one at all you can just match the .375 as you see it. Otherwise use it a while and see if you want to mess with it. Just for grins check out the net for the older pre 64 .375 H&H with the big scoop or U notch in the bridge. If it works as is, other changes would be done only to improve reliability, ease of loading or aesthetics. One last comment about looking around the net and looking at the .375 receiver. Many .375 type rear mounts use a large rear base or even the same base as the standard action. As a result you can wind up with a mount base that overhangs the ejection port a lot. This cuts into your freespace needed for rapid reloading. If your rifle is iron sight only it is of no concern. If you scope your rifle you may want to redrill and/or shorten the rear base to clear the loading/ejection port.
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What do you plan on hunting? If this is a bear gun, the last thing you want is to have to gingerly pussyfoot your cartridges when recharging your magazine. For the Wby cartridges, you really should use the H&H action which is made for the longer magnums, not the std length magnums. I have a 340 Wby built on a '49 H&H length action. Great gun, great cartridge. Good luck. There are two types of people in the world: those that get things done and those who make excuses. There are no others. | |||
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FMC: Thanks for the input I was looking for a different Elk hunting rifle to match my 300 H&H rifle. For Bear if needed I have a 375 H&H, 416 Rigby, 460 WBY or lastly my 500 Jeffery just incase. Take Care and Merry Christmas Brad | |||
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