Visiting Belted Magnum Brass Again

The PPU case separation thread inspired me to ask this question again. Resizing belted magnum brass? It seems the general consensus is to headspace from the shoulder when handloading. I am particularly interested in 375 H&H brass. OK, here's my question: The belt on magnum cases is there for the cartridge to headspace on, is this correct? So, after fireforming, first or second firing, it is recommended to just bump the shoulder back
.002 or .003 thousandths. And then the handloaded cartridge supposedly headspaces from the shoulder. Is this correct?

So, in the meantime nothing was done to change the cartridge belt dimension from the original dimensions. Cartridge base to belt that was established so that the cartridge would headspace off the belt. I question if FL Resizing or just bumping the shoulder .002-.003 actually
prevents the cartridge from continuing to headspace from the belt?

So, what's the consensus of this very knowledgeable group?+

1) Yes, the belt on a magnum case is there for the cartridge to headspace on. The original engineering concept was based on the shoulder angle being so slight in order to facilitate cordite insertion and feeding that the belt was required.
2) After the first firing just neck size and anneal. No need to bump shoulder back until bolt closure has resistance.
3) Yes, after first firing cartridge will headspace off shoulder.
4) Keep brass with the rifle chamber it was fired in only. Do not mix with other rifles of the same chambering.
5) The cartridge will now fit that specific chamber perfectly and by neck sizing only will center the bullet in the bore for improved accuracy. The cartridge chamber snug fit continues to allow headspace support from the belt. The important improvement is eliminating case stretch immediately in front of the belt.

Schüler Jumbo said:

1) Yes, the belt on a magnum case is there for the cartridge to headspace on. The original engineering concept was based on the shoulder angle being so slight in order to facilitate cordite insertion and feeding that the belt was required.
2) After the first firing just neck size and anneal. No need to bump shoulder back until bolt closure has resistance.
3) Yes, after first firing cartridge will headspace off shoulder.
4) Keep brass with the rifle chamber it was fired in only. Do not mix with other rifles of the same chambering.
5) The cartridge will now fit that specific chamber perfectly and by neck sizing only will center the bullet in the bore for improved accuracy. The cartridge chamber snug fit continues to allow headspace support from the belt. The important improvement is eliminating case stretch immediately in front of the belt.

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3) what is preventing the cartridge from continuing to headspace from the belt?

Thanks for your reply.

Nothing is preventing the belt from being a contributing part to the fired case headspacing. See note #5. In fact, because of the tight shoulder and belt tolerance working in tandem to support proper headspace is the reason to keep brass assigned to the rifle it was fired in.

Ok, since i only have one 375 H&H, keeping it separate is not an issue.

So depending on the tolerance stackup between the chamber and belted brass the cartridge could be more or less headspaced off the belt or shoulder?

I’ve mentioned somewhere in another thread that the cartridge belt to chamber belt recess can vary by up to 0.010” , 0.006” over the recommended limit of 0.004” and that was just on one rifle
Gumpy

When the unfired round is chambered the belt determines headspace. When the round is fired the case head is held in place between the bolt face and belt and the brass body in front of the belt is stretched until the brass shoulder contacts the chamber shoulder stopping brass elongation and under pressure “jammed” into the chamber walls and chamber shoulder cut. Now, as pressure subsides the brass has “spring back” of .001” - .002” which is what allows the bolt to open. At the same time there is “back thrust” exerting a force on the bolt face which the bolt lugs hold the face in place. This spring back is why the shoulder does not require immediate set-back but after a few firings the spring back is diminished making it difficult to close the bolt then the shoulder is bumped back and case annealed. At the same time the case neck is lengthening and will require case trimming or else the case neck will jam into the throat making bolt closure difficult and increasing internal pressure because the neck will have no tolerance to expand. So, while we are dealing in thousands of an inch in brass expansion and brass spring back the belt and case head remain fixed thus the belt continues as prime headspace until brass is in inelastic state and remains in even constant full contact with chamber shoulder.

Schüler Jumbo said:

When the unfired round is chambered the belt determines headspace. When the round is fired the case head is held in place between the bolt face and belt and the brass body in front of the belt is stretched until the brass shoulder contacts the chamber shoulder stopping brass elongation and under pressure “jammed” into the chamber walls and chamber shoulder cut. Now, as pressure subsides the brass has “spring back” of .001” - .002” which is what allows the bolt to open. At the same time there is “back thrust” exerting a force on the bolt face which the bolt lugs hold the face in place. This spring back is why the shoulder does not require immediate set-back but after a few firings the spring back is diminished making it difficult to close the bolt then the shoulder is bumped back and case annealed. At the same time the case neck is lengthening and will require case trimming or else the case neck will jam into the throat making bolt closure difficult and increasing internal pressure because the neck will have no tolerance to expand. So, while we are dealing in thousands of an inch in brass expansion and brass spring back the belt and case head remain fixed thus the belt continues as prime headspace until brass is in inelastic state and remains in even constant full contact with chamber shoulder.

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Great explanation, thank you very much.

Grumpy gumpy said:

I’ve mentioned somewhere in another thread that the cartridge belt to chamber belt recess can vary by up to 0.010” , 0.006” over the recommended limit of 0.004” and that was just on one rifle
Gumpy

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Thanks, how would i go about measuring that clearance on my rifle?

I can probably find some tutorials on YouTube, but does anyone have their preferred method of setting a Full Length resizing die to just bump the shoulder back by .001" or so? In my case, I'm using 308 Norma Magnum RCBS full length dies. I also have a neck sizing die set as well.

So as a beginning hand loader (haven't done it yet despite having all the tools) am i reading this right, that is better to neck size 375H&H brass instead of full length sizing?

RSL said:

Thanks, how would i go about measuring that clearance on my rifle?

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In the 338 I was referring to, the tools used were a surface plate, an accurate micrometer height gauge and a depth gauge as well as a chamber cast, not the sort of tools everyone has unfortunately
Gumpy

Axle2010 said:

So as a beginning hand loader (haven't done it yet despite having all the tools) am i reading this right, that is better to neck size 375H&H brass instead of full length sizing?

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Maybe… As others have said, if you can find someone who knows what they are doing to watch them, it is a good start. If using brass fired in your rifle , neck size to start, then make sure the case will chamber in your rifle, no bullet, just the case. If it’s tight, then give the die a quarter turn down lock it tight again and give the case another resize and try it again in your rifle, but it should chamber easily the first time with just the neck size. If new brass , full length size it to make sure it’s uniform, then neck size. You will need to FLS brass after several neck sizing,, or if the case is at all tight to chamber.
Gumpy

Grumpy gumpy said:

In the 338 I was referring to, the tools used were a surface plate, an accurate micrometer height gauge and a depth gauge as well as a chamber cast, not the sort of tools everyone has unfortunately
Gumpy

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Thanks, as it happens i actually have those tools, except the stuff to make a chamber cast. I built Porsche racing engines for many years. Unfortunately, it's all in storage, I hope, at my nephews shop in Missouri. I am in AZ and probably not gonna move that stuff before I am out of here for good. I did order a Forester Field
Headspace gage for belted magnums. Just to check things out. I don’t suspect a problem with my 375 H&H M70 but I am a gear and tool freak, so....

Anyone reloading belted magnums would be well advised to get a Larry Willis die….

Didn’t know about it until last year and it’s been a game changer!

It is also important to know how your rifle is chambered. My current love is the Browning BLR. The three factory barrels I own, all came chambered sloppy from the factory. That is not a bad thing on a lever action rifle, since it lacks the strong camming action of a bolt action. They will close on a belted magnum go, no go, but not on a field gauge. Currently I have a factory 300 win mag, and from 7mm Rem mags, I have built a 338 win mag and a 375 Taylor (aka 375/338). Technically they are safe, but they will never be target quality. I get about 2 moa. OK for hunting the way I do.

My opinion is that with these beasties, we never headspace on the belt. The first firing moves the shoulder forward, and I then just bump it back, usually after 3 firings. I also trim at this point. I also try chambering the brass after resizing, when it works, I am done. Wash, rinse, repeat for each round (in groups of three) as I load the cases. If you think about it, the brass has to come from somewhere, and you can just feel the depression ahead of the belt with a paper clip. So I expect a short case life. For some reason I normally get some neck splits on the 5th firing in the 300 and 338. I just toss the brass on the 5th firing. I do not want to junk the rifle from a case head failure.

So I am in the camp that in this rifle, the belt is just decoration. I might (if you can get the barrel out of the barrel extension) set the barrel back and headspace off the belt. However, giving up the slop, will probably give up function. I'll take function and 2 moa accuracy.

RSL said:

Thanks, as it happens i actually have those tools, except the stuff to make a chamber cast. I built Porsche racing engines for many years. Unfortunately, it's all in storage, I hope, at my nephews shop in Missouri. I am in AZ and probably not gonna move that stuff before I am out of here for good. I did order a Forester Field
Headspace gage for belted magnums. Just to check things out. I don’t suspect a problem with my 375 H&H M70 but I am a gear and tool freak, so....

Click to expand...

I’m weirdly excited and jealous( re the engines), not many have the gear , let alone know how to use it.
Gumpy

arniet said:

For some reason I normally get some neck splits on the 5th firing in the 300 and 338. I just toss the brass on the 5th firing. I do not want to junk the rifle from a case head failure.

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A few comments:
1) Anneal the brass after every two firings and I suspect that will eliminate the neck splits.
2) Measure case length before trimming to ensure trimming is required and if so, then only trim minimum amount.
3) Only neck size until shoulder bump back is required.

My Forester Belted Magnum Headspace Gauge arrived today. My 375 H&H passed the gauge test. The bolt would not close on the Field
Length Gauge. So alls good. I can post some photos tomorrow if anyone is interested.

Yes, post the photos.