Necking up weatherby case you .378WM specs

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Fairly newish to reloading. Most to date has been your normal cartridges.... 308, 6.5cm 223, and a little 338LM.

A friend and hunting buddy on mine owns a beautiful Wby Mk5 in 378 Weatherby Magnum. Not a .30-378 or .338-378 but the .375 caliber projectile based round.

Dies and brass appear tremendously difficult to find for that specific caliber. So far, Wolverine GT is the one place I’ve found that actually has some supplies, and at $95 for 20pc new brass... yikes that’s expensive.

In the interest of cost savings and availability of brass I had an idea. I think everyone has heard of manufacturers necking cartridges down to fit a smaller diameter projectile on a case, but can the same apply in reverse? Ie is it possibly to purchase .30-378 or .338-378 1F brass and “neck it up” to accept .375 cal projectiles? If so would this be done with the mandrels in a specific die? Would any FL 378wby die work? Would I need to fireform brass using COW or other method? Is it just a pipe dream?

Your help is greatly appreciated!!
 
I have used COW method to blow out 7mm Rem Mag into 458 Win Mag; others have done same from 300 Win Mag cases. Your challenge is that 378 Weatherby has virtually unique rim and belt size - I don't know of any other case with that size to form from, except those derived from that case - you do mention two - the .30-378 and the .338-378. It is larger diameter rim/belt than 375 H&H and all the other "standard" belted magnums. My first thought was that to use toys like that one, need a wallet or checking account sized appropriately... You probably want to download the ANSI/SAAMI cartridge and chamber standards and confirm some dimensions.
 
The 378 cases cant really be made by anything other then the 378 case family. They are fricking huge.

The 375 cases can easily be made by any case that is long enough and based off the 375 h&h case

If you want to make 378 cases out of 30-378 or 338-378 you can just fire them in the 378 rilfe to form them.. or you can use fired cases ans just load them with some pistol powder and COW and fire them. Or just use an expander and open them up to 375

Or you can buy the 416 or 460 weatherby cases and neck them down.

Half my 460 cases say 460 on them and the other half say 416 on them as there was a smoking deal on the EE and i paid 2$ a case for new unfired 416

But yes its super comon to neck up or down cases to makes others.

If you had a 30-378 case and didnt want to shoot it to size, id run a 338-35 cal expander in it then id just send the big ole case into the 378 die.
 
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Evanguy said:
The 378 cases cant really be made by anything other then the 378 case family. They are fricking huge.

The 375 cases can easily be made by any case that is long enough and based off the 375 h&h case

If you want to make 378 cases out of 30-378 or 338-378 you can just fire them in the 378 rilfe to form them.. or you can use fired cases ans just load them with some pistol powder and COW and fire them. Or just use an expander and open them up to 375

Or you can buy the 416 or 460 weatherby cases and neck them down.

Half my 460 cases say 460 on them and the other half say 416 on them as there was a smoking deal on the EE and i paid 2$ a case for new unfired 416

But yes its super comon to neck up or down cases to makes others.

If you had a 30-378 case and didnt want to shoot it to size, id run a 338-35 cal expander in it then id just send the big ole case into the 378 die.
Click to expand...


All correct, with one caveat! If you are necking up once fired brass, you should anneal the neck first, or else it might split.
 
Thank you to everyone who has responded. While .30 and .338-378 use the same parent case, it seems they’re much more readily available and so in a pinch we’re something I was looking at for cost savings. I wasn’t considering using any but them for try to make some .378wby brass.

I don’t have an annealer though, so perhaps just best to go with the 378 case from the get go. For those of you who load for wby magnum, how many reloads do you find you’re getting with your brass without annealing?

257wby: I’ll be reaching out to you directly
 
Cartridge brass is usually a copper (70%) and zinc (30%) alloy, or thereabouts. Very few people have access to a proper hardness tester, so usually see a neck "split" or crack and attribute it to "hardness" or becoming brittle. The alloy becomes brittle by "working" it - every time it is expanded by firing or constricted by re-sizing, it gets a bit more "brittle". I don't load for that kind of Weatherby, but in my 300 Winchester and 338 Winchester, the primer pockets get loose, before I experience neck splitting. And, my thinking is that I will run those magnums "hot", or may as well use smaller cartridges, so I think my pressures are right up there, which strains the primer pocket end.
You actually probably have an "annealer". Since virtually no one has a hardness tester, what "works" to anneal has many variations. A common old school version is to simply twirl the case with the neck in a candle flame until the case body is too hot to hang on to - those that do it this way as as adamant that their cases are "properly annealed" as the people with $1,000 "annealing machines" - but neither usually have the hardness tester to confirm - both are going with lack of case neck splits, and some claim to be able to tell the difference in "seating pressure".
 
pacobillie said:
All correct, with one caveat! If you are necking up once fired brass, you should anneal the neck first, or else it might split.
Click to expand...

Youre correct most times that is the best idea, but i found with necking up weatherby brass i was better off not to anneal them as much as other shaped cases as the radius shoulder would allow it to collapse when they got soft. After every 0.050 jump i annealed the top of the neck staying away from the shoulder area. So depending how how far you were going you may not have too
 
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