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I was wondering about necking a 300 H&H up to 338. Would a guy be able to re-chamber a 338 Win Mag?

Nope... Too much taper on the case to "re-chamber" a 338 win mag. No benefit to doing what you are wanting either.. . Some downfalls to going with a case with that much taper as well..

Yup,BSA is right.

This, was done in the 1920s in Britain and by O,Neil, Keith and Hopkins about the same time.....largely what inspired the superb .338WM.

They did their homework too. No need to try and re-invent the wheel huh buddy..

simplyme;
Good evening to you sir, hopefully the Saturday treated you well.

So unless I'm missing something here, what you are talking about is a .340 Weatherby is it not?

The case length for both is pretty close - 3.563" for the .340 and 3.6 on the nose for the H&H case.

Anyway, if memory serves I think that I've yet to fire a .340 Weatherby, but did have a .338 Win Mag for a half dozen years before I had it rebarreled into a .308 Norma.

There's no flies on the .338" bullets and if you're heading north to chase the big critters then they'd be a perfect match for each other.

Hopefully that was useful information to you sir and all the best to you this weekend.

Dwayne

Dwayne, there's a big difference between the 340 WBY and what the OP asked. He may decide that is what he's ultimately looking for, but it was my impression that he's wanting to re-chamber a 338 win mag and neck up a 300 H&H. Necking up a 300 H&H is not a 340 wby. and one can not simply re chamber a 338 win mag to make this happen. Too much taper on the H&H case. Dimensions and taper of the H&H makes for a not so likely endeavor....Like Kute has already mentioned, OKH developed a cartridge in the 40's. It used the .333 bullets instead of the .338 bullets of today. It was a 300 H&H necked up to a .333 cal and was made obsolete after the introduction of the 338 win mag in 1958. If you look at the dimensions of the H&H cartridge and compare it to the 338 win mag, you'll notice that the case diameter is too small near the shoulder on the H&H round. Thus, you can not simply re-chamber a 338 win mag while using a necked up H&H cartridge. The chamber would be too sloppy to allow for this and would split the case at a minimum or even blow the gun up. Hope this makes sense..

bsa1917hunter;
Thanks kindly for the additional explanation/correction.

I do believe you're correct on all counts - and what you'd end up with would be a .340 Weatherbyish sort of case by the time the taper is taken out.

Thanks again sir and all the best to you this weekend.

Dwayne

No problem my friend. My first thought was "340 WBY" as well, but had to think about what the OP was really asking. I may be taking his question too literally. Your response may be what he is looking for. However, he'd have to then re-chamber his 338 win mag to 340 wby and that is do-able. I believe..

I gave it some serious thought at one time but in the end I didn't do it. It's a cool looking cartridge that I'm sure would feed with the best of them. The problem is the actions need so much work and it offers no ballistic advantage over the .338WM.



Terry

Yup the cartridge was part of the OKH line of cartridges developed by Charlie O'Neil, Elmer Keith, and Don Hopkins in the 30's. The 334 OKH was based on the 300 or 375H&H case necked to .333(British caliber) and drove a 250 gr bullet about 2800 fps.

It had a shoulder and long neck.

The cartridge also had a little brother in the form of the 333 OKH based on the 30/06 case;and later another called the 333OKH belted which was shorter than the 334 and much like the 338 WinMag.

The 340 Weatherby is nothing more than a necked down and blown out 375H&H case; it is also just a 300 Weatherby case necked up,Both derive their origins from the 375 and 300 H&H cases.

So a 300 H&H necked up today is not going to do anything a 340 Weatherby won't do. It's a very old concept and OKH did it all years ago.

Bob, great post but I don't think the necked up 300 H&H is going to do anymore than a 338 win mag will do (let alone the 340 wby). The taper on the 300 H&H will reduce case capacity and equal that (86 grains of water for each case) of the shorter 338 win mag: Thus no gain. Except for the fact that it will be a little slicker feeding...

Something else to consider, most .338 bullets have a longer Ogive with the cannelure's set back further on the bullets shank.

This would mean if you seated say a 225gn Hornady to the cannelure in the .300 H&H case, the OAL would be extended beyond the original .300 OAL dimension and perhaps not work through a 3.6" magazine.

Moving to a .340 Weatherby is likely easier and more practical for most people.

John

OKH changed their cartridge to .338 when .333 bullets became difficult to obtain, as EK wrote several times.

I think that a .338 on the H&H case, sans "blow out" as Powell, et. al., did and Weatherby popularized is a rather poor idea and the Winchester folks got it right in the late '50s, except they should have followed Newton's original concept a la .375 Ruger.

bsa: The velocity figures were not mine. They were from an article by Bob Hagel on the OKH cartridges:

".....Ralph Avery,who did a lot of experimenting with the 334 OKH cartridge,had several chronograph checks made by Joyce Hornady. I (Hagel) have copies of these reports which show velocity to be very good using H-4831 powder....A charge of of 80 grains of this powder behind the Barnes 250 gr bullet,with an over all cartridge length of 3.75 inches,gave an average muzzle velocity of 2895....." Bob Hagel; "OKH Cartridges"; Guns, Loads,& Hunting Tips.


I understated in lifting the info.

TC1 - so that's a .338H&H of your making on the right in the photo?

Did you just neck the case up? Are people here saying that there would be so much headspace that if fired in an actual chamber the case would split?

And if that is the case, couldn't a chamber be made that would exactly mirror the case you made so that the headspace wouldn't be excessive?

Thanks for the info Bob. That's some good stuff. It just seems weird because the case capacity is identical to the 338 win mag. We both know what displacement is and like you've said before and I quote: "There's no replacement for displacement".. . I'm sure Hagel and OKH probably pushed the envelope and pressures of the cartridge to really make it sing..

Good point John..

Yes, I made it and no, case splits or headspacing wouldn't be any more of a problem than a .300 H&H. Being an old magnum case you simply headspace off the belt. That's what it's there for. It would work every bit as well as a .300 H&H. A chamber reamer is a simple matter too. The bullet cannelure can just be ignored if even necessary like on so many other wildcats and you can get dies for it too.

The problem's I found with it were A. The rifle action would require a little extra work for the H&H cases. Not really a big deal but it's a consideration and B. Like most other wildcats out there, it didn't offer any real advantage to whats already on the market.

I toyed with idea for a while but decided I didn't want one bad enough to pursue it. I can't think of any reason why it wouldn't work if that's what you want.

Terry

I had a similar idea, wanted to build a full length H&H MAgnum 338 and so simply necked up the 8mm RemMag case to 338 for my 340 Tyrannosaur. I get 3100fps from 225gr Barnes TTSX bullets (Exact same speed the 338 Lapua round gets with those according to the Barnes Manual), and can use 340WBY or 338 Winchester Magnum ammo in my rifle if I need to or want to. Case making is a snap, just run an 8mm RemMag case through a 340WBY or 338 Win Mag re sizing die, but only enough of it to push the neck out to take the new .338 bullets.

I have been shooting this round for about 20 years now, and really like it on larger game.