# resizing pistol cartridges



## fencer (Mar 8, 2012)

Does the 357 cartridge case lengthen? Is it necessary to trim the case?


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## VAMarine (Dec 25, 2008)

.357 Magnum or .357Sig?


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## fencer (Mar 8, 2012)

357 magnum


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## Steve M1911A1 (Feb 6, 2008)

Eventually, almost all cartridge cases lengthen from repeated firing and resizing.
Straight-wall cases like .357 Magnum will be less affected than will bottleneck cases like the .357 SIG.

The best way to tell is to get either an inexpensive micrometer or a case-length gauge.
To use the micrometer, measure an unused or once-fired case, and then use that figure to assess other cases.
Case-length gauges are drop-in affairs, with little "steps" machined into them that do the measuring for you.


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## rex (Jan 27, 2012)

I'm not sure but I believe they do.I don't believe it's as fast as bottleneck rounds though.Straightwall auto rounds like the 45 or 9 actually get shorter over repeated firing and resizing.


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## Steve M1911A1 (Feb 6, 2008)

rex said:


> ...Straightwall auto rounds like the 45 or 9 actually get shorter over repeated firing and resizing.


Um, no.

Less-stressed cartridges like the .45 ACP don't lengthen much, but firing and resizing will cause brass to stretch. It's inevitable.


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## rex (Jan 27, 2012)

Myself and alot of other reloaders disagree.I don't remember the physics but I believe the general concensus is the brass flows to the head in these cases.When I shot alot over time the shoulder of SWCs were sticking out of the case more than new brass with the same OAL,I never measured it and just accepted it after learning about it 20 some years ago.You are the only person I've met that says otherwise,I know nobody that has ever trimmed 45 or 9 brass,and I shoot them until the mouth splits.


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## Steve M1911A1 (Feb 6, 2008)

rex said:


> ...I know nobody that has ever trimmed 45 or 9 brass,and I shoot them until the mouth splits.


My experience exactly.

But the cases do not become shorter. They just don't lengthen.


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## noylj (Dec 8, 2011)

Never seen a straight-wall case grow. They shrink.
Only reason to trim .38 Special or .357 Magnum is so the roll crimp is consistent.
You will find that with the fixed Lee case trimmer, almost none of your cases will even be as long as the trim-to length.


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## usmcj (Sep 23, 2011)

I've never had an issue with, or trimmed the case on a .357 mag, or any other handgun cartridge that I reload. Having said that, I'll just go find a piece of wood to "knock" on... :smt1099


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## rex (Jan 27, 2012)

Steve M1911A1 said:


> My experience exactly.
> 
> But the cases do not become shorter. They just don't lengthen.


That's basically what I got asking a few heavy reloaders.

The way it was explained to me is the upon firing the case naturally swells and shortens,we all know that.When you resize it it doesn't quite go back to original length.This happens the first few loadings,slightly getting shorter,but then it tends to stop or become much less and hover at that length from then on,work hardening being suspected for the lack of further change.That makes more sense than brass displacing since pistol brass doesn't get worked as hard as rifle brass.


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## Steve M1911A1 (Feb 6, 2008)

That seems like a very good explanation of the phenomenon.
Thanks.


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