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30-378 neck forming and belt removal questions

Hello all, I am looking for some advice/help. I have been reloading for about 12 years now but I have run into an issue and need help. I just bought a used 30-378 with a 338 neck. It came with fifty new 378 belted cases that have not been necked down. It also came with some loaded cases and fired brass. All of the loaded cases and fired brass have no belt. I can see the trim marks so this 378 brass has had the belt removed. The Full Length sizing die has “No Belt” stamped on the side as well. So, my issue is two fold. How do I trim off the belt and size the neck on the new brass? I ran 3 pieces up the Die but ruined all three by “mushrooming” the bottom of the neck. I did some internet searching and came across a thread mentioning that I need to neck turn some of the brass off the 378 brass first so that there was not so much brass to be sized and this would keep the bottom from “mushrooming”. Is this the correct method? Lastly, I am confused on the 338 neck. Does this mean that I cant buy 30-378 brass since the neck is .337 or do I go ahead and load 30-378 rounds, shoot them and the neck will then form to the .338? I have rifles where I neck turn down but none that “turn up”. My dies are “No Belt 30-378 with .338 neck”. Looking for the best way to handle all of the above. The used and loaded brass will only last so long so I would like to be able to make my own. Thank you in advance for any and all help. David
 
Caveat: I have no experience with that cartridge, but:

30-378 implies that you have a .30 caliber rifle; the 378 refers to the original cartridge it was based on prior to being modified to hold a .308 bullet. Interestingly, a bit of research shows the standard .30-378 to be a belted cartridge. (link below)

The 338 is the interior diameter of the neck portion of your rifle's chamber. That becomes important when you get to a loaded round, as the neck portion of the cartridge will have a diameter of (bullet diameter + twice brass neck thickness.) If the brass is too thick, it can't open to release the bullet, causing pressure problems. Sizing brass down from a larger neck diameter to smaller will increase the thickness, which may necessitate turning the thickness of the neck down.

As I said at the outset, I am going by experience with other cartridges here; I don't know the 30-378 specifically, so take all this with a grain or two of salt.

Link to info:
https://en.wikipedia.org/wiki/.30-378_Weatherby_Magnum
 
I have lots of experience with the 300 win mag...

Do NOT remove the belt. Once you fire the brass with a full power load, you may proceedin to headspace the resizing from the shoulder just like any other non-belted cartreidge.

All you need is the Hornady Headspace comparator kit and calipers.

After firing the first batch of brass, use the headspace comparator to bump the shoulders 0.002".... this will negate all the negative aspects of the belt and make it into a belt-less cartridge sizing procedure.

Hence why you need the Hornady comparator kit and calipers.
 
Just an example....

Before sizing...

IMG_20190823_234241.jpg


After sizing....


IMG_20190823_234144.jpg


Than's a 0.002" shoulder bump we're after.

Thus the belt becomes irrelevant !!!
 
The first thing you must know is if the chamber was done with a reamer that had no provision for a belt. If there was no room cut in the chamber for a belt chambering a case with a belt still on it is going to be impossible to accomplish. Load a dummy round (no primer and no powder) measure the neck of the dummy round with a bullet seated in the neck. If the neck measures less than the .337 number you posted then no neck turning will be required (it will need a little clearance). If it measures bigger than .335 you will need to neck turn the cases.
 
Here is a piece of the same brass after being fired FULL THROTTLE at least several times...

I used a dremel to chop it in half to check for any brass thinning near the base. You be the judge.

Sectioned_300winmag.JPG
 
Hello all, Ebb is correct. I have @ 50 pieces of used and loaded brass, with no belt, that chamber. I was sent 50 pieces of new 378 brass, with a belt, that will not chamber. The chamber will not take a belt at all. I ruined the 3 pieces of brass trying to reform the neck by barely running the brass up the resizing die. I mean barely any pressure at all. The die has "no belt" written on it so this rifle is a 30-378 Weatherby with a .338 neck designed for beltless brass. Trying to figure out how the belt was removed and then how to resize the neck without "mushrooming" the neck at the shoulder. As mentioned before, I did read something that mentioned I need to "turn the necks" on the 378 brass to get rid of some of the brass so that it is not so "thick".....(not sure that this is the correct way to say it). Does this sound right? Otherwise, how do I resize the neck of the 378 brass that I have? All of the used brass that came with the rifle is 378. None is 30-378 brass. Then lastly, I am confused on the 338 neck. Does this mean that I cant buy 30-378 brass since the neck is .337 or do I go ahead and load 30-378 rounds, shoot them and the neck will then form to the .338? Thanks again!!
 
Yes, after the first or second firing the belt is no longer in play.
That 30-378, is that with the usual Weatherby radius shoulder?
Also l wonder the purpose behind the belt removal.
Holland & Holland started it with their 300 H&H because there really was no shoulder.
Maybe Ed Weatherby liked the way it looked. Radius shoulders, huge freebore, unreal performance, 9 locking lugs…. he surely thought outside the box.
Like Gerald Bull, a free thinker!
 
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I believe your first course of action would be to try and contact the original owner of the rifle and get the specs on the chamber. He should be able to give you all the pertinent info that you need. Giving advice without knowing the specs could be dangerous. JMO

Add: My 30/378 Weatherby mag loaded round with Weatherby brass measures .333 and fired unsized brass measure .337. It would be safe to assume with .001 spring back that the chamber would be .338. JFYI
 
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Thanks Murray, I agree but have not had any luck getting any info. The best info I have is @ 50 pieces of brass that is ready to go, the bullet, the load data and the die that has "no belt" stamped on it. The rest is a mystery.
M-61, from what I can tell, other than the belt being removed, the shoulder is the same.
 
If that is the case then I would take some measurements and compare to factory 30/378 cases. Length, neck # before bullet seating, neck # after bullet seating as well as the neck # on fired unsized brass. I would also measure the 200 line ( just in front of where the belt would be) and compare to a factory load. Maybe all your specs are the same as the Weatherby ones minus the belt.
 
Hello all, I am looking for some advice/help. I have been reloading for about 12 years now but I have run into an issue and need help. I just bought a used 30-378 with a 338 neck. It came with fifty new 378 belted cases that have not been necked down. It also came with some loaded cases and fired brass. All of the loaded cases and fired brass have no belt. I can see the trim marks so this 378 brass has had the belt removed. The Full Length sizing die has “No Belt” stamped on the side as well. So, my issue is two fold. How do I trim off the belt and size the neck on the new brass? I ran 3 pieces up the Die but ruined all three by “mushrooming” the bottom of the neck. I did some internet searching and came across a thread mentioning that I need to neck turn some of the brass off the 378 brass first so that there was not so much brass to be sized and this would keep the bottom from “mushrooming”. Is this the correct method? Lastly, I am confused on the 338 neck. Does this mean that I cant buy 30-378 brass since the neck is .337 or do I go ahead and load 30-378 rounds, shoot them and the neck will then form to the .338? I have rifles where I neck turn down but none that “turn up”. My dies are “No Belt 30-378 with .338 neck”. Looking for the best way to handle all of the above. The used and loaded brass will only last so long so I would like to be able to make my own. Thank you in advance for any and all help. David
Gator
Hello all, I am looking for some advice/help. I have been reloading for about 12 years now but I have run into an issue and need help. I just bought a used 30-378 with a 338 neck. It came with fifty new 378 belted cases that have not been necked down. It also came with some loaded cases and fired brass. All of the loaded cases and fired brass have no belt. I can see the trim marks so this 378 brass has had the belt removed. The Full Length sizing die has “No Belt” stamped on the side as well. So, my issue is two fold. How do I trim off the belt and size the neck on the new brass? I ran 3 pieces up the Die but ruined all three by “mushrooming” the bottom of the neck. I did some internet searching and came across a thread mentioning that I need to neck turn some of the brass off the 378 brass first so that there was not so much brass to be sized and this would keep the bottom from “mushrooming”. Is this the correct method? Lastly, I am confused on the 338 neck. Does this mean that I cant buy 30-378 brass since the neck is .337 or do I go ahead and load 30-378 rounds, shoot them and the neck will then form to the .338? I have rifles where I neck turn down but none that “turn up”. My dies are “No Belt 30-378 with .338 neck”. Looking for the best way to handle all of the above. The used and loaded brass will only last so long so I would like to be able to make my own. Thank you in advance for any and all help. David
Gator
30 years ago I made a 30-338 with no belt.
Got me in the Wimbledon final twice.
I can walk you thru it but not typing on my phone.
Call me Monday at the shop. Ill dig out the 200 pics I have and the reamer drawing.
All I remember now is it was removing the belt, sizing to a false shoulder. Shot on call in the x ring right away.
Alan Warner
 
You should be able to save big bucks reloading for that cartridge. I was in Sportsman's Thursday browsing the ammo reloading section. They had Weatherby brand ammo at a mere $105 a box of 20.
 
I stopped reading comments after zero333. I have a 338-378 weatherby there’s a huge column of powder you’re dealing with!… the first thing I would do based off your first post would be to cast your chamber!… you have no idea what they have done here. Like zero333 said once fired you headspace off the shoulder anyways. I shoot 104 grains of rl22 and 125 grains of 870 I realize yours is some different being .308 but still that’s a lot of powder, cast your chamber so you know what your dealing with
Wayne
 
Big problem is if it's not virgin brass and it's already been fired in another chamber you might have chambering issues.

There is a company out there that can help solving this issue with a small base type of collett that will squeeze a little bit more right above the belt.

I was lucky I was able to overcam the press enough without any issues.
 

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