Overpressure? Fired out of Battery?


August 26, 2011, 05:06 PM
After polishing some 9MM range pickups, I found these four bulged cases. I don't know anything about what they were shot from or if they were factory or reloads. I do know that they are not from my reloads (primer color is wrong). I'm just trying to gain a little insight on what may have caused this for later reference. Thanks.

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Friendly, Don't Fire!
August 26, 2011, 05:09 PM
If the bulge is not all the way around the case, there are some guns that are unsupported where the feed ramp meets the chamber. With that, you will typically see a small bulge, shaped like an open-mouth, kind of round on the semi-circular top (looking at the side of the casing while it is standing on its base).

The flattened and cratered primer does look like overpressure, and it may be that the load was so hot, there was still pressure as it was ejecting, causing the bulge. It may have been a load someone was working up. I hope whoever it is realizes that anything like hotter ammo on a hot day can cause the pressures to spike, thus possibly blowing the base off the case before it is ejected!

One other possibilty could be water that might have frozen thus expanding the case. However, that would have nothing to do with the flattened, cratered primer!

August 26, 2011, 05:11 PM
Looks like overpressure to me... scary

August 26, 2011, 05:20 PM
Man, that was quick. The bulge does go all the way around. Two of the cases had a primer and two didn't. Thanks for the replies.

Friendly, Don't Fire!
August 26, 2011, 05:22 PM
I see you are fairly new here, WELCOME!

Ooops, now that I see you have been here since 2008, it is more like WELCOME BACK!


August 26, 2011, 05:28 PM
I come here quite often (daily). Most of the time if I need information, I can do a quick search and find what I need to know. There's lots of knowledge floating around here. Normally if I have anything that I can add to a thread, it's been stated already. Heck, I've learned stuff here that I didn't even know that I needed to know.

Friendly, Don't Fire!
August 26, 2011, 05:34 PM
Thanks for clarifying that!
Welcome back!
(again) ;)

August 26, 2011, 10:19 PM
Wow, I'm going with over pressure. I've never seen a case buldge like that with an AL handgun cartridge, and I load near maximum all the time. It deffinitely looks like the presures were still rising excessively during ejection. I wouldn't think that would be too good for the 9mm they were fored from.

August 26, 2011, 10:31 PM
Definitely over-pressure...firing out of battery won't do that to a primer.

August 26, 2011, 11:09 PM
I load lots of 9mm with range pickups that have been "glockified." Meaning a bulge at the base. Those are not typical. Yikes!:uhoh:

August 27, 2011, 02:21 PM
Another possibility is that the cases were fired in an open-bolt submachine gun, such as an Uzi. I have seen fired cases exactly like this, and the chamber was dirty, so cartridges weren't entering tha chamber before ignition.

Jim Watson
August 27, 2011, 05:16 PM
Agree that it is out of an open bolt gun that fired a little TOO open.
I have seen empties like that out of the old original TEC-9.

August 28, 2011, 02:50 AM
Maybe this (bottom of post #17) - http://thefiringline.com/forums/showthread.php?t=230344

Jim Watson
August 28, 2011, 12:39 PM
Probably not a bulge into a sloppy feed ramp, considering that the finder says:
"The bulge does go all the way around."

August 28, 2011, 02:23 PM
The photos in that link look a great deal like these. The ones that I picked up weren't quite as severe, though.

August 29, 2011, 12:50 AM
If all the bulges are the same. I would think they were fired from a very poorly supported chamber. Don't think a open bolt gun. I don't think they are seeing a lot of over pressure. That one primer does not show any true excessive over pressure IMO. And appears to have been fired in full battery/lock up. As for the primers falling out or missing. With a bulge like that in the brass and in that area. The primer hole could easily been deformed to the point it would not hold a primer.

While that looks like a sever Glock bulge it was not fired out of a Glock with a OEM slide.

I would not like to be the shooter firing that weapon at all.

August 29, 2011, 01:44 PM
I've also seen cases similar to that fired from an open-bolt full-auto. The cyclic rate was such that the round would be extracted before chamber pressure had fully dropped, causing a bulge in the case.

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