What would cause this?

G

ghbucky

New member
Shooting at a match today, one guy switched his glocks over for a minute and we noticed a very discolored case showed up in the brass pile. He fired a couple of others from that gun to confirm, and each case ejected from that specific gun showed very heavy carbon on only one side of the case.

He was shooting fiocchi 9mm ammo, and his other glock did not produce cases like that.

The theory was that the chamber was misshapen, but I'm not convinced that would cause it. In my mind, if there wasn't a good seal on the chamber, the entire case would have shown burn marks.

I'm just curious as to what this indicates. Any ideas?
 

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Specific to 1 gun but repeatable.
~1/2 the case is discolored, factory ammo.
Sounds like one gun is not properly / fully chambering the round or the chamber is distorted.

But hey, it's a plastic glock :D
 
I've seen similar in a much smaller and more 'wedge-shaped' way on various pistols in the past - most chambered in 9mm.
That is more significant than I've seen and does appear that the chamber may not be sealing well and there is blowback into the chamber after ignition. ?
 
I'm thinking it could be case not expanding to full expansion to seal the chamber due to low pressure loads.
 
I'm thinking it could be case not expanding to full expansion to seal the chamber due to low pressure loads.
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That could cause that kind of thing, but one would think that ammo with that problem would exhibit that behavior in any gun, not just one gun.

Also, in my experience, Fiocchi tends to be loaded pretty hot.
 
9x19 is a tapered case. It doesn't take much in the way of headspace or chamber
diameter to create a significant amount of space for some carbon/gas.
 
He was shooting fiocchi 9mm ammo, and his other glock did not produce cases like that.
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There you go.
Something is out of whack with the barrel (chamber to be more precice).

If it's bothersome, see if Glock will cover it under warranty.
I doubt it though but you can always try.
I's simply gas blowing past the case.

If it's really a bother to you - get an HK or an old (pre 1940-something) Luger.
They use George Luger's 1910 patent - "offset obturation"or 0.1mm chamber step which he thought up to ensure the chamber sealed gasses when firing the tapered case 9mm.

Tapered cases - like the 9X19 uses have had accuracy problems from inception.

To help overcome this & address some of the gas blow by - some makers use what's known as a "stepped chamber".
Just google it - there's tons of information available & like I mentioned above - it's no real mystery since it goes back 110 years or more.

Edit - actually - "accuracy problems" - isn't really fair since the 9X19 was never intended to be a target round. It's plenty accurate for the job it's called on to do. Saying "accuracy problems" about it is sort of like saying the 911 Porchse has gas milegae problems.
 
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JohnKSa said:
That could cause that kind of thing, but one would think that ammo with that problem would exhibit that behavior in any gun, not just one gun.

Also, in my experience, Fiocchi tends to be loaded pretty hot.
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Just re-read the whole thing again, I see what you mean.
 
He should do a casting of the chamber than do a concentricity check with a gauge if he has one, or just take it to a gunsmith.
 
I have seen similar marks too, but not to this extreme and consistency. I almost wonder if there is something in the chamber - a sliver of lead or something coating part of one side? - that is keeping the brass from expanding and sealing on that side. I would take a close look inside or do a thorough cleaning and see if it improves.
And forgive me if this has already been done and I am being too simple / stupid.

GB!
 
It may be an optical illusion in the pic but there appears to be belling on the discolored side. I would run a good set of calipers around the case mouth to look for out of round as well as from the mouth back clocked @ several angles to look for chamber variations. It seems that the chamber is most likely out of spec.
 
There's probably a sliver of copper or lead stuck in the chamber, causing the cases to:
A) offset, and
B) not seal properly early enough.
...If that's carbon.

To me, they look like sharpie-colored cases.
 
I've seen solvent or oil do that before. It usually burns off after a few rounds. One good reason to be sure to clean chambers with a dry patch before shooting.
 
To me, they look like sharpie-colored cases.
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It was definitely carbon. I was able to scratch a line in it with my fingernail.

Interesting idea about the solvent or oil. I don't think he fired 5 shots out of it. I don't know the guy outside of shooting with him at that match, so I have no idea on history of the gun or his maintenance.

I was just curious, because I'd never seen anything like that before.
 
I tend to think it was caused by low pressure ammo in relation the the malleability of the case material. The only way to determine if it is a chamber issue or related to the specific ammo would be to mark the case orientation and see if the discoloration is always on the same side of the chamber. Then use a different brand of ammo and see if it repeats.
 
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