belted mag case head to shoulder expansion

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brasscollector

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What is a safe maximum for case head-to-shoulder expansion on new or once-fired brass?

Recently acquired some free 300wm ammunition which I have pulled down, decapped and tumbled. Being curious I ran the 19 pieces through my Hornady comparator and came up with about .020" difference between other once-fired cases and these 'freebies'. Just for reference that would be approx .012" shorter than some new, unfired Hornady ammunition I had left.

Edited to (hopefully) clarify: The once-fired cases I am speaking of were not fired in my rifle. The once-fired cases were re-sized by another individual to shorter than minimum spec ammunition. The Hornady brass (ammunition) will expand .008" in my rifle.
 
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What is a safe maximum for case head-to-shoulder expansion on new or once-fired brass?
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No one measures before and again after. No one saves new unfired cases for reference.

In the big inning the belt was designed to hold the case to the rear; what ever happened in front of the belt was of no concern. The body of the case was designed to fill the chamber.

And then comes the full length sizing die, reloaders size the case with total disregard for the length of the chamber from the shoulder to the bolt face. Had they measured before and again after firing they would know how to adjust the die. A problem' reloaders do not know the if the die and shell holder has the ability to restore the case to minimum length.

If you found cases that are .020" longer from the shoulder to case head than the cases you have sized and or fired you should know how to adjust the die.

I do not bump the shoulder because bump sounds like an accident and it is not possible to bump the shoulder back. I know; that sounds complicated, so does the part abut the belt holding the case to the rear. Reloaders have no clue what happens to the shoulder when the case is held to the rear with the belt. Again, in the big inning the purposes of the case was to fill the chamber when the belt the case t the rear.

Reloaders assume the case stretches between the shoulder and case head.

F. Guffey
 
And then it gets complicated.

What is a safe maximum for case head-to-shoulder expansion on new or once-fired brass?
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Stretch is one thing and expansion is another Many reloaders are under the illusion the shoulder on the case moves when fired. If the shoulder moves when fired the rifle chamber and case have conflicts.

I know; I am told the firing pin drives the case forwarded until the shoulder of the case collides with the shoulder of the chamber and I always hope that does not happen because (of it does) there is no way to prevent stretch between the case head and case body.

F. Guffey
 
Brasscollector,

If I understand your question, the part Mr. Guffey quite correctly identified as complicating matters, one answer was worked out by P.O. Ackley long ago. His Ackley Improved cartridges take a parent cartridge and blow the outside of the shoulder forward and out. Moving them forward on the order of a tenth of an inch was no issue for him. You just fire a loaded parent cartridge in the AI chamber and it formed the case for the bigger chamber. In addition to Ackley, I've even seen .308 cases that were forced into a 30-06 chamber and fired. They have no neck left, but I haven't seen splitting or other problems. They just aren't really usable afterward, as Ackley's are.

The main thing is just not to do this too often, or it will work harden the brass until it splits. If you were to resize and push the shoulder back to the original new length, that will happen. However, if you want long case life, do as Mr. Guffey suggests: Measure from head to shoulder after firing and before resizing. Adjust the die until it just pushes the shoulder back below that as-fired number. One to two thousandths is enough for feeding, as the case will have been narrowed by the sizing effort, too. That case may not fit another chamber, but it is adequate for yours and minimizes work-hardening and brass fatigue. If you don't worry about feeding, but are loading one round at a time, you may be happy with neck sizing only.

The bottom line here is that unless it was previously resized small like that several times, you probably don't have a problem. But do take the time to use a bent paperclip and feel around inside at the forward edge of the belt to see if you feel a thinning pressure ring. If you do, unfortunately, the brass is pre-worn out for you.
 
Whew, glad someone understood my question which was clear as mud. , thank you.
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As in Unclenick does and I didn't?

The main thing is just not to do this too often, or it will work harden the brass until it splits. If you were to resize and push the shoulder back to the original new length, that will happen.
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I always ask; "how is it possible to push the shoulder back?" When I move the shoulder back the case bulges between the shoulder and case head. All of my full length sizing dies has case body support.

I am not one of those; "I experimented etc. etc.. ..Types" but I have turned cases into accordions or for the lack of a better description 'cases with bellows'. I 'actually' pushed the shoulder back and shortened the distance from the shoulder to the case head. When finished the cases had no functional value and were impossible to chamber; but! I did manage to move the shoulder back.

F. Guffey

Dufus, thank you.
 
Guffey you not only understood but answered the question. My issue is I like to keep things as simple as possible. I would prefer not to get hung up over terminology and nuances out of my control. So in light of that I am going to continue pushing the shoulders back on my cases, perhaps even bumping them occasionally. :eek:
 
Having a belt and a shoulder is a lot like having a belt and suspenders.

The brass belt is probably between 0.212 and 0.215"[ brass factories typically make belts at the low end of the 0.212 to 0.220" range].
The chamber is probably about 0.222". [Rifle factories typically headspace 0.002" over SAAMI minimum while I headspace mine 0.005" less than minimum for real world brass]
That means the OP's bras is probably between 0.007 and 0.010" of sammi slop..er..er.. belt clearance.
While we would like that to be between 0.001 and 0.002" so the case does not stretch, it does mean that the 0.020" measured [to the shoulder I assume] is irrelevant. [The belt holds up the pants in this case, not the suspenders]

If someone want to get really fussy, they can expand the neck and then partial neck size the brass down to just touch the tiny false shoulder around the brass neck to the chamber shoulder. The late gunsmith, Randy Ketchum, back in the 1990s had a 243 that was headspaced too long by one thread turn. He always expanded the neck and made a partial shoulder for it.

Alternatively fussy people can fire form brass. 10 gr pistol powder covered with cream of wheat with moly grease [50 kpsi grease] rubbed on the sides of the case. Shoot straight up, or if at the range, plug the neck with Ivory soap to keep the cream of wheat from falling out when shooting horizontally.
 
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