Neck Sizing Vs. Full Length Sizing and Neck Tension

Mikecr

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I was thinking what Tiny Tim was saying is if the die is over sizing and bumping the neck down a whole lot more than it should be, then a lot of brass gets pushed down in the case body flowing until it can't go past the belt.
Sizing moves brass thick toward thin. That's up cases(forward), not down them(back).
 

Mikecr

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What happens if you oversize or over bump the shoulder down? Where does the brass go?
Brass thickness moves up toward the mouths. The donut area will grow in thickness, and eventually you'll be trimming at mouths.
The case with high headspace will stretch back to the bolt face on firing. This will cause thinning at a point low on the body where the case finally did not have enough grip with chamber walls to prevent the stretching. Then when you squish that stretched case back into proper head spacing, you will move brass thickness up the case (not into the thinned area), so that thinning cannot be restored to normal.

Cases taper in thickness from webs all the way to mouths. Notice that your sizing actually begins low on the case, moving upwards. This rolls brass thick toward thin, near webs all the way to mouths.
This changes cartridge character a little bit with each cycle, and these changes cannot be countered with the same process that creates them.
So unless it's in your plan to accept this change (through sizing and/or replacement), then it's best to minimally size.
 

nksmfamjp

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The case with high headspace will stretch back to the bolt face on firing. This will cause thinning at a point low on the body where the case finally did not have enough grip with chamber walls to prevent the stretching. Then when you squish that stretched case back into proper head spacing, you will move brass thickness up the case (not into the thinned area), so that thinning cannot be restored to normal.
Is that true considering how a magnum headspaces on the belt when new?
 

Veteran

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Brass thickness moves up toward the mouths. The donut area will grow in thickness, and eventually you'll be trimming at mouths.
The case with high headspace will stretch back to the bolt face on firing. This will cause thinning at a point low on the body where the case finally did not have enough grip with chamber walls to prevent the stretching. Then when you squish that stretched case back into proper head spacing, you will move brass thickness up the case (not into the thinned area), so that thinning cannot be restored to normal.

Cases taper in thickness from webs all the way to mouths. Notice that your sizing actually begins low on the case, moving upwards. This rolls brass thick toward thin, near webs all the way to mouths.
This changes cartridge character a little bit with each cycle, and these changes cannot be countered with the same process that creates them.
So unless it's in your plan to accept this change (through sizing and/or replacement), then it's best to minimally size.

If what you outline here is in fact the case....(no pun intended), then I ought to be able to verify it by measuring COAL before and after sizing...... So if the case length grows by all the sizing causing brass to migrate to the mouth of the case, then the length will be more after I size and bump the neck down according to your outline of how it happens......

Intuitively at least, it does not make sense to me that the case length will in fact get longer, even if I am bumping and sizing it down.
I have always heard and thought that the brass gets shoved down onto the belt where it has to stop migrating. But, I am willing to keep an open mind and conduct a few experiments to try to verify this new outline you give that the brass always moves to the case mouth and therefore the COAL must increase. I guess we can see.
 

Veteran

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Do you own headspace comparators?
I do not yet own head space comparators, only the bullet ogive comparators for getting the jump measurements to ogive correct.
But, I am headed that way I suppose. It seems like a good way to measure the shoulder movements in resizing for sure.
 

Recshooter64

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Back to the original question. I ran into the same problem with my 7mm Rem Mag. The third firing some were getting stuck in the chamber. After inspecting the brass, I noticed marks above the belt. I compared the diameter of the fired brass with new brass and found that the fired brass had grown as much as .002”. I did a little research and found a collet die made to reduce this area back to .500”. I have bought the die but haven’t tried it yet. The reviews are good so I am hopeful. I’ll report after I resize and try again.
BTW it is a Larry Willis Belted Magnum Collet Resizing Die sold by Reloading Technologies.
 

brant89

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If what you outline here is in fact the case....(no pun intended), then I ought to be able to verify it by measuring COAL before and after sizing...... So if the case length grows by all the sizing causing brass to migrate to the mouth of the case, then the length will be more after I size and bump the neck down according to your outline of how it happens......

Intuitively at least, it does not make sense to me that the case length will in fact get longer, even if I am bumping and sizing it down.
I have always heard and thought that the brass gets shoved down onto the belt where it has to stop migrating. But, I am willing to keep an open mind and conduct a few experiments to try to verify this new outline you give that the brass always moves to the case mouth and therefore the COAL must increase. I guess we can see.
It’s pretty well known that cases get longer throughout the firing/sizing cycle. That’s why you have to trim them periodically. If the cartridge is getting longer, but the base to shoulder (headspace) is constrained by the rifle chamber and sizing die (which it is), then the case MUST be getting longer in the case neck. Everything else is constrained. So if the case neck is getting longer, but we aren’t adding any material to it, then where is the extra brass coming from? The answer is the case body, usually in the web just above the case head. The body gets thinner as it stretches to fill the chamber, but doesn’t get pushed back to it’s original thickness when sizing because the die only constrains the outside of the case, not the inside.
A case won’t necessarily get longer after FL sizing vs. before (though it might), but it WILL get longer after a few firing/sizing cycles either during firing, or sizing, or both. This can be minimized be properly setting your dies for a minimal shoulder bump, maybe even to the point that you wear out primer pockets before ever needing to trim (like my .260AI after 10 firings), but the cases are still getting longer to some degree which means the case body must be getting thinner. Steeper shoulder angles help to minimize this as well which is one of the biggest benefits of AI chambers.
 
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Mike Matteson

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Here what I did in about yr 2000. I purchased a 300 WM neck die for my 308 Norma Mag rifle. The different is the 308 NM is a little shorter case to the shoulder than the 300WM, which made the neck shorter on the 300WM case. ( I use 300WM cases for my 308NM) Back them I was loosing case do to head separation in about 4 or 5 firing if I recall. I shifted to the 300WM necking die, which only sized the 308NM neck about half way. The case separation stopped. Due to I was using hot loads, my primes pocket were then become enlarged in about 10 to 12 firing. I also had problem with neck splitting in only a few firing also. I started annealing my cases after first firing, and that stop the neck splitting. (In the water in the pan annealing) That was only one time annealing. I was at the time cutting my necks for thickness. So I didn't bump my cases. My grouping did tighten up some or about 1/2" @ 100yds.
If I read correctly you can adjust your FL die to only bump the shoulder back a few thousand. You will need a comparator set up to check how much you are bumping the case. Somebody smarter than me should be able to clear this up some. You can get a Redding or others with bushing sizing die and set up your bumping setting. I have just purchase the comparator equipment here as of late. The equipment seen to be in short supply at times(which I got was Sinclair).
From what I have lesson too, and watch YouTube the Match shooter @ 1000yds are bumping there case back about .002 or so. I haven't put the bumping into practice yet, but that were I am headed for. This applies to most all belted magnum case.(To clarify) That from 264WM, 7mm Rem Mag, 300 WM, 308NM .338WM. Others belted Magnum case I haven't used or don't have any info to what you can or can't do.
If I remember correctly Peterson brass makes longer 300 WM case to the shoulder for reloading.
My has this Long Range shooting has changed my ways of thinking, and I feel to the better.
 

brant89

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I would also add that it usually takes two or three firing for a case to stretch to full chamber length. I know this because I run zero headspace on my brass and always find a little more spring-back in the brass in the first couple firings. I only point this out because if you set your FL die on the first firing and never adjust it after that, you might have more than your targeted .002" headspace.
 

Veteran

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Yes, I have seen the brass growth a lot the first 3-4 firings and fall off after that..... I hate trimming! Its the worst part of reloading for me. Its just a chore. I recently upgraded to the Lyman machine.....haven't used it yet, but its gotta be better. So, yes, this is a good point you make, that almost nothing in reloading seems to be set and forget........(like that moss cleaner wet and forget).

Looks like I have to be more disciplined to check everything 3 times after every firing. Adjust my dies as the brass the changes and measure it constantly to see where I am on headspace, trim length, and chamber fit,etc..
 

Veteran

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Just purchased the head space comparator set from Hornady at Midsouth. Lucky, I guess, it was in stock. Natchez and others were sold out......stuff sure is hard to find these days......can't believe Powder Valley says powder may get worse, and there are no primers in
sight until a year or more......Will trade Large Magnum Rifle Primers for Gold. 1 Primer, 1 ounce of gold!😜 LOL
1 mansion with built in shooting range for a whole brick!
 
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