fireforming 300 Weatherby cases to 375 Weatherby?

[rp85]

good evening:

is fireforming new unfired .300 Weatherby cases to .375 Weatherby possible? If possible suggested method? what issues I might face, i.e. case neck to thick? just asking to making sure. thanks for any input.

regards.

rp

[Mk42gunner]

It should be okay, after all when Roy Weatherby first came out with his cartridges the only brass available was the .300 and .375 H&H.

Given prices of components these days, you might be money ahead to invest in a tapered expander to take the case necks from .30 to .375.

Robert

[PositiveCaster]

I agree that a tapered expander is likely a better idea. I’ve fireformed .223 cases to 7TCU by simply firing factory .223s in the 7TCU chamber, but not sure how that method would work with the larger, thicker brass. The shoulders are far different in those two cases too and will probably require FL sizing anyway. The neck will get thinner when expanded, not thicker.



.

[blackthorn]

Not exactly on topic but years ago I fire-formed 300 H&H to 300 Weatherby. I just used them for hunting, and I found them more than adequate for hunting Deer etc. When done, I had a 300 Weatherby case with just a slightly less interior capacity than factory Weatherby brass.

[Kosh75287]

You can try it and see, but I think straight fire-forming to expand a case neck by .070" (that's a 23% jump in diameter) will get you a lot of split necks and ruined brass. There's virtue in gradually expanding the case neck by running it over a .311" (or slightly larger) expander, then .323", then .338", then .348", then .358", then .366", to .375". I'D consider annealing before you start (at .308"), then after .338" or .348", then after you have your desired neck diameter. I know that this requires "cornering the market" on expander balls, but these are typically more available than usable brass for which such conversions are contemplated.
At some point, you will figure out which stages in these expansions are unnecessary, and you can omit them from the progression. Until you do, I recommend a gradual if laborious sequence, and annealing at the beginning, middle and end of the process.
If you own or know someone who reloads for 8x56R Mannlicher, the .329" would ALSO be a good intermediate step.

[Onty]

good evening:

is fireforming new unfired .300 Weatherby cases to .375 Weatherby possible? If possible suggested method? what issues I might face, i.e. case neck to thick? just asking to making sure. thanks for any input.

regards.

rp
If I am in your situation, I would sell .300 Weatherby brass, purchase .375 H&H and use it.

Just for your info, there is another excellent cartridge, .375 JRS, created by Jon Sundra. Apparently, ballistically identical to .375 Weatherby. Advantage of .375 JRS is that to make a brass all is needed to neck up 8 Remington Magnum. As a matter of fact brass 8 Remington Magnum is available https://www.grafs.com/catalog/category/categoryId/788 .

Here is post from another forum:

#3 · Mar 7, 2015

It's too bad that this post is so old and there was never any appreciable activity on it. I have a custom built 375JRS in a M-98 (Vz-24) action and love it. I built the rifle with a McGowen barrel and had the barrel Nitrated. It is very accurate and can drop virtually anything in it's tracks. I would not hesitate to use it on anything in Africa. In the Americas or Eurasia it WILL drop ANYTHING in its tracks. I is about the most powerful rifle anyone would ever need for ANYTHING. There is a lot of overkill out there but this is a nice balance. I never regretted it for building the rifle. The cartridge is actually better than the older 375 Weatherby because the brass lasts longer. I have loaded some as many as seven or eight times. But also I only neck size to make the brass last longer.

https://www.go2gbo.com/threads/375-jrs-any-opinions.82543/

[15meter]

Semi-related, my go around with forming 458 Win Mag from a plethora of other similar belted cases.

You may find a hint or two buried in this thread to help you on the way:

https://castboolits.gunloads.com/showthread.php?431146-Fire-forming-458-Win-Mag


And neck thickness is usually only a problem either when going down in diameter as in .243 Winchester from .308 or dramatically shorter as in .223 Remington to .221 Fireball.

Hope it helps.

[rp85]

good morning;

first, thanks for all the input.

yesterday actually compared side by side a 300 wby case with 375 wby case. surprised at the difference of the shoulder on each case, way to much for my liking. cases were nearly free but not worth the trouble to me.

know a 300h&h case will work if you anneal the cases first. have @ 175 375 wby cases but can always use more. thanks again for input.

regards

rp

[414gates]

good evening:

is fireforming new unfired .300 Weatherby cases to .375 Weatherby possible? If possible suggested method? what issues I might face, i.e. case neck to thick? just asking to making sure. thanks for any input.

regards.

rp

Fireforming is certainly possible if the original case can chamber.

I neck 7mm RUM to 375 RUM in two passes with mandrels, with anneal after each mandrel sizing.

I use a .308 mandrel to get from 7mm to .308, then use a .375 mandrel.

Case neck thickness should not be an issue for you.