how much expansion is too much


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lopezni
August 6, 2010, 10:54 PM
I have been getting about .003" expansion around the case head area from .472 to .475 after firing a cartridge, is this too much? the cases tend to be harder to reload as they go from first fired to last and the primers start to flatten out, not completely though and no cratering. This is with the same amount of powder in each case. Is this a problem?

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ranger335v
August 7, 2010, 08:28 AM
It would be for me.

Hondo 60
August 7, 2010, 11:00 AM
You don't say what caliber, what powder, how much powder, what bullet or the OAL.
As long as you stay within published loads I wouldn't be too concerned.

But from what you DID say, it sounds like that's not the case.

If you're loading them hotter than published data, YES it's a problem.

lopezni
August 7, 2010, 11:42 AM
it is 6.5x55 SE and 140gr SPBT 3.050" oal and 43.3 gr RE-22. Well within the limits of the cartridge. This only happens with about 50% of the cases.

Ridgerunner665
August 7, 2010, 11:49 AM
It could be that the firearm has a "generously" sized chamber...

Robert Wilson
August 7, 2010, 12:28 PM
Are you using Norma brass? It is often quite soft, in my experience.

Where you are measuring is also important. If you are measuring just ahead of the web, with a blade micrometer, .003" indicates something is seriously wrong. If that is the situation, I would discontinue all use of the rifle and take it to a gunsmith.

I suspect, though, that you are measuring some other portion of the case, probably with a standard micrometer or dial caliper, and are seeing the typical expansion one can expect of the lower portion of the case body.

For what it's worth, I don't consider case head measurements a good gauge of pressure or safety. There is too much disparity between individual rifles and individual brands of brass. Especially now that we have cheap, reliable chronographs, I have given up measuring case heads.

rcmodel
August 7, 2010, 02:44 PM
I agree .003" case head expansion is about .0028 more then you should ever see on any rifle case. That would be measured on the solid part of the case head right in front of the extractor groove.

However .003" case web expansion is perfectly normal. That would be measured about 1/4"-3/8" foreword of the extractor groove were the case wall has tapered to a much thinner section of the case.
All that much expansion of the web indicates is a loose chamber.

.003" case head expansion would indicate a very dangerous over-pressure load and would result in loose primer pockets on the first firing, if not a blow-up.

rc

lopezni
August 7, 2010, 03:19 PM
you're right, the actual "case head" expansion is negligible. where I was noticing the slight bulge was about .215" up from the extractor groove. I only noticed it in about 8 of 15 cases.

Innovative
August 7, 2010, 06:24 PM
lopenzi .......

This is a much better indication of chamber pressure from your handloads. The picture shows 4 fired cases that had increasing powder charges. Notice the flatness of the primers. (Picture came from my website.)

http://www.larrywillis.com/pressure%20signs.jpg

Robert Wilson
August 8, 2010, 12:25 AM
How much pressure was generated by each load?

918v
August 8, 2010, 12:38 AM
If your case heads expanded .003", your primers would fall out. You are measuring case body expansion, and your numbers are meaningless without a reference to factory ammo using the same brand case.

R.W.Dale
August 8, 2010, 12:49 AM
What brass are you using?

Domestically made by any chance?

What does the unfired case head measure?

Those of you with experience with 6.5x55 will see where this is going

It could be that the firearm has a "generously" sized chamber...
or undersized brass

918v
August 8, 2010, 01:35 PM
How about that brass typically expands .003" to seal a chamber?

R.W.Dale
August 8, 2010, 01:43 PM
How about that brass typically expands .003" to seal a chamber?
QUE???

918v
August 8, 2010, 01:44 PM
He's not measuring the case head.

R.W.Dale
August 8, 2010, 02:03 PM
But we need to know what size the case head IS before firing.

Here's why

Domestic 6.5x55 brass makers have gotten lazy (OMG not americans!! ) of late and started making brass with a undersized 473" or 30-06 sized case head rather than the proper .480" case head. this right there could account for the over expansion the OP is noting due to the case being unsupported just north of the case head

918v
August 8, 2010, 02:16 PM
The OP said the unfired case measures .472" at the expansion ring area, so I figure he must be using domestic brass.

.003" expansion in this area is prolly OK, but we need a basis for comparison. Being that his chamber is tapered, the more case expansion, the higher the pressure.

R.W.Dale
August 8, 2010, 02:30 PM
Change to a spec case from a european manufacturer and I'll wager the "problem" will absolutely disappear.

918v
August 8, 2010, 03:21 PM
My question is:

If his unfired case measures .472" and his fired case measures .475", will a .480" case even chamber?

R.W.Dale
August 8, 2010, 03:32 PM
My question is:

If his unfired case measures .472" and his fired case measures .475", will a .480" case even chamber?
His cases probably aren't expanding all the way out to the chamber walls just above the case head and are springing back a bit after firing as well.

If he has a SAAMI or CIP 6.5x55 or 6.5x55skan chamber then a .479/.480" case will fit in there as snug as a bug in a rug and come out after firing looking like a new piece of brass

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