308 headspace question.

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nemesiss45

New member
I got a bunch of lapua .308 brass that had been sized for 7mm-08. I dont have a 7mm-08, so i sized a few back up to 308. Problem is, they are a hair short on my headspace gauge, about .004 under the low mark on the gauge and about .006 shorter than my fire formed cases. Will i have any problem fire forming these? I was thinking maybe i should anneal them before i try?

Thanks
 
Problem is, they are a hair short on my headspace gauge, about .004 under the low mark on the gauge and about .006 shorter than my fire formed cases.
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nemesiss45, if I had a "you bet, no problem and right away" answer I would give it to yo0u, but, I don't.

.006" shorter than my fire formed cases
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Shorter in length from the mouth of the case to the head of the case or .006" shorter from the datum of .400" round hole to the head of the case??

about .004 under the low mark
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At the low mark the case is full length sized/minimum length. if the case length is .004" below the low mark your cases are short and could present a problem. Firing a case that short would be the equivalent of firing a full length case in a no go-gage chamber. When fire forming the case could stretch .009" between the case head and case body, that is bad.

Then there is the assumption all receivers are alike and most reloaders want to give the short answer.

F. Guffey
 
The .006 is based on the case gauge. The lapua cases are .004 uner the minimum, the fire formed are .002 over the minimum.
 
the fire formed are .002 over the minimum.
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I am the only reloader that used a straight edge with the Wilson case gage. With the straight edge and a feeler gage I know the length of the case from the datum to the case head in thousandths. If the cases are short by .006" and the formed cases are over .002" over minimum the difference in length between the chamber and the case when measured from the shoulder to the case head is .008".

In my world there is no such thing as a short case from the shoulder to the case head. I do not find it necessary to fire a case in a chamber just to determine what will happen. I am told it is a waste of time to determine the length of a case from the shoulder to the case head. I have purchased factory ammo and measured each for length between the shoulder to the case head, I have been impressed.

.006" short? It is not likely the chamber the cases were fired in was a short chamber, had you measured the length of the case from shoulder to case head before necking up you would know if necking the case up compressed the case. I have had cases shorten .045" in length from the mouth of the case to the case head, going from .284" to .350 is a work out. Most of the .045" was in the neck.

F. Guffey

I am the fan of standards and transfers.
 
I did not measure them before, but did toss a few in the case gauge. They were short about the same amount, but i didnt know how reliable that was since the neck size was too small.

Anyway, i decided to try fire forming a few cases using a little red dot and cream of wheat. I lit one off this morning and it formed up great. Ill try a few more when i have some time
 
Cartridges do not have headspace.
If the cases are a couple thou shorter than the Trim-to of 2.005" there will be no problem. Over the max case length of 2.015" can give grief, but in between or a tick short will not.
The only real issue you might have with necking up is too thin of a neck. If the case neck measures .343" diameter you're fine.
 
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