Undersize 40 Caliber Brass


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Old 02-26-2010, 03:34 PM   #1
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Default Undersize 40 Caliber Brass

For some reason the ammunition manufacturers have become notorious for using short 40 caliber brass. I have found, over the last 6 months, once-fired brass as short as .820". Oh, it still loads and fires but, what is it doing to my extractor?

{insert BIG thank you, to those who leave their brass on the range}

The rimless straight wall cartridges are the only type of cartridge where head space is dtermined soley by case length. Do we get all caught up on checking maximum head space and forget all about minimum head space?

Too little head space (brass that is too long) does not allow the round to fully chamber. Excessive head space (brass that is too short) allows the round to chamber too deeply.

The rim of the cartridge "seats" against the end of the chamber, so when the firing pin strikes the primer the round is not moved forward. In the case of brass that is too short and does not touch the end of the chamber, the only part keeping the round from moving further into the chamber is the extractor claw (at least that is the way I see it). So, when the firing pin strikes, it slams the (short) case forward against the extractor claw. Can this lead to a broken extractor?

Food for thought ?



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Old 02-26-2010, 03:46 PM   #2
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Dave, were you measuring the brass before it was resized, or after? Brass will sometimes be shorter due to the case bulging out after firing. It should go back to spec after sizing. Also, repeated use of brass can make it shorten over time from the force of the slide slamming the case mouth into the rim inside the barrel that it headspaces on.

MotorG20



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Old 02-27-2010, 12:19 AM   #3
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I have found that my Lee resizing die causes the brass to "grow" 4 to 6 thousands.

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Old 02-27-2010, 11:23 AM   #4
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Quote:
Originally Posted by Dave_Bone View Post
I have found that my Lee resizing die causes the brass to "grow" 4 to 6 thousands.
This is consistent with what I saw when measuring fired and then re-sized 9mm and .45 ACP. BUT, I believe that the cases get "shortened" in the firing process, i.e. the cases expand in diameter when fired and the case length is thereby reduced. Re-sizing the brass then forms the brass back to the correct outside diameter and the brass is then returned to (near) it's pre-fired length.

Take a control set of cartridges fire them, measure the fired cases before sizing, then again after sizing, re-load and fire, then repeat the measurement process. I would be surprised if the cases grow in length much at all in the overall process.
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Old 03-01-2010, 02:04 PM   #5
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This phenomenon will be more pronounced in loose chambered guns (ie: Glock). There is more bulging, especially at the base and thus more length "shrinkage" from firing.

And, to answer you OP question: Yes excessive headspace (from too long a chamber or too short a cartridge) can cause extractor breakage. I seriously doubt you will finid range pick up brass that is so short as to cause extractor problems. Remember the rim is slammed against the extractor hook by the firing pin, but the rim is still brass and much softer than the extractor. You will likely see damage to the rim on a case that is excessively short.

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Old 03-02-2010, 01:06 AM   #6
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I was wondering why the 40 S&W cases that I use would buldge like that at the base. I have certainly noticed this phenomenon when I shoot my .40 S&W Sigma. I am not sure what you mean by a "loose chambered" gun? How is a glock or other glock like gun (ie: S&W Sigma) loosed chambered. I am relatively new to these pistols and have not read or heard the term loose chambered. Also Mr. Robocop10mm, IN the few short days I have been reading posts on this site, I have learned a ton from your posts, so thank you sir for helping and informing new guys like myself.

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Old 03-02-2010, 02:31 AM   #7
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Field strip your pistol. Remove the barrel. Insert a loaded round into the chamber. Note that the base of the case is nearly flush with the hood (the small squared projection that would be on top). Wiggle the case in the chamber. This wiggle is more pronounced in the Glocks than in most others. The Sigmas are a bit tighter. A "match" barrel will have much less movement (or slop). The tighter the round fits into the chamber, the more the accuracy "potential".

Now look opposite the hood at the feed ramp area. You will note that there is some brass exposed (or unsupported). This area allows the brass to swell during firing as there is nothing to hold it back. Glocks have a reputation for bulging more at this point than most other guns. Your Sigma will have some unsupported area, but it is the rear most part of the case that is thickest and the most resistant to deformation during firing.

This unsupported area allows greater expansion and then requires more work to return to original specs. Brass will "work harden" from being expanded and resized repeatedly. WHen it hardens it also gets more brittle. This is the area Glocks "blow out" when they Kb (Kaboom).

This is a simplified explanation and by no means the difinitive answer for Glock Kb's.

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Old 03-02-2010, 11:05 PM   #8
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I have been waiting for a reply from the USPSA staff. Now that I have that, and valuable input from this forum's members, I can make an educated guess. Err, I mean decision.

Typical trim length is .010" below maximum case length, before resizing. This is right in line with what I have been doing. As for short cases, I am setting my own standards, based on the information I have been given. I am going to discard brass less than .835", again, before resizing.

Knowing that the cases "grow" .004" ~ .006" in the resizing die I use, this will make my resized brass .839" to .846" long.

I reference unsized brass here because I use a progressive press. So, my trimming has to be done before resizing.

That's my plan, and I'm stick'n to it

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Old 03-03-2010, 12:36 PM   #9
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Dave:

Your interpretation of published “trim to” lengths being before resizing is a new one to me. I have always used the maximum case length and “trim to” dimensions from my re-loading manuals as being referenced to a sized case.

I once was overly paranoid about case length on my 9mm and .45 ACP (which I reload on a Dillon RL-550), and it was a pain to resize, then measure/trim a batch of cases and then start the reloading process on the progressive press. I asked the question here, and got the same advice from Robo that he has given to you. I (being and engineer and often anal about some things) had to prove it to myself that the 9mm and 45 ACP cases really do not grow significantly to warrant all of that work associated with trimming. I did the measuring process I had described in an earlier post and TA-DA, Robo was right. I no longer worry about it.

Before I realized I was wasting my time trimming the 9mm and .45 brass, I had worked out a strategy similar to yours where I would trim to the “trim to” length before resizing knowing that I would get a .003”-.005” increase in case length form the re-sizing step and that the re-sized case would be in the “acceptable” case length range. But again, once I started working on cases I had previously trimmed, and therefore knew what the original case length was, I proved to myself that I was wasting my time.

I also load .223 in a progressive press (old Dillon RL-450-B). Here I DO worry about case length and I do a separate re-sizing step on my RCBS single stage press, then trim every case with a Lee case trimming tool (cutter - lock stud type) chucked into my drill motor. Then I start the batch of brass through the RL-450. I DO trim every .223 case because most of the .223 I reload is range pick-up brass with significant variation in case lengths.

Anyway I am not trying to start an argument, and you can do whatever you feel comfortable with.

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Old 03-03-2010, 10:17 PM   #10
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Paxil?! Good gawd, just what I need, another med.



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