We came back from the range a week or two ago and with the cases that we’ve fired we seemed to pick up a rogue case.

In sorting En properly picked the 10mm from the pile of .40 that we shot. They are basically the same case, but the 10mm is a bit longer and it uses a large primer to set it off. Looking at it I quickly found something amis with it.

Of course that’s not what a proper 10mm. The jagged edge is a dead giveaway.

Left: Proper fired 10mm case. Right: Recovered 10mm case with a lateral split.

Looking at the primer, while not an exact science, really told the story.

This was shot out of a Glock. I’m going to presume that it’s out of a Glock 20 since I’ve never seen anyone with a 29. You can tell that it’s from a Glock because of the peculiar rectangular firing pin channel. Of course in this instance it actively flowed into the channel and completely flattened itself against the breech face as well.

Even the head-stamp shows a bit of distress.

The 10mm cartridge is really hand loader’s cartridge. It doesn’t have a lot of guns that are chambered for it as well. That being said it is a large-capacity cartridge and you can easily tune the load from a very light load to a real barrel-burner. The Starline brass is another piece of evidence since they mainly cater to handloaders. (I have seen Starline on a commercial loading from Fiocchi in .40 S&W, but I’ve never seen it elsewhere)

Putting the pieces together I can only guess that this particular case was overcharged, perhaps double-charged.

Here’s what it should look like, compared to the blown up round:

The case on the left shows no signs of the primer flowing at all. You can still see the radius at the edge of the primer as well. The head stamp seems significantly clearer as well — though that in and of itself isn’t enough to go on since I don’t have any other examples of what 10mm Starline brass looks like. Incidentally you can tell the good case was also fired out of a Glock, perhaps out of the same one. (I picked up the good case around a year ago; the broken case is from a week or two ago)

Here’s another example of a fired large pistol primer in a different (and lower pressure) case:

I don’t have any unfired factory large primer case, but they look a lot like the small primers.

All of these are from Winchester white box 9mm. Their still in their original case in this picture.


Here’s all of the fired large primers in one picture for comparison purposes.

I just wonder what happened to the gun when this round was touched off. Certainly it left some of itself in the chamber of the gun… How bad was it?

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