What caused this?

[WartHog]

Random range pick-up 9mm

[rice_man]

Probably been reloaded a few times.

[Catch]

A dozen reloads? Or out of spec chamber?

[whutsup40]

Ouch!!!

[Cowboy T]

That case looks like it has a fair amount of scratches on it. I'd say it's been well used and finally gave way due to that use. That's a good thing; it means people are reusing their cases.

The other possibility, though I'm not seeing the typical signs, is that a 9mm case got fired in a .40 S&W pistol. Usually, when that happens, you'll see a large, and sudden, expanding of the case just forward of the case head, along with the split. If it was a NATO case--NATO brass tends to be thicker on average--then there would be less expansion with that crack. But I'd still expect to see *some* case expansion.

[hermosabeach]

I shot some ammo from the 1930's and they split lengthwise

if was new ammo- brass was brittle....


As others said- lengthwise crack can be brittle brass


Hit it with calipers too.... I have seen 9MM fired from 40 S&W

some rugers will fire an entire magazine... the brass is not supported by 1MM when it fires and some might split like that

[bigbossman]

Old age, over-use. It happens.

[Snoopy47]

Old age, over-use. It happens.

Yea, not a big deal. It's never caused a squib for me, but the loss of pressure through the side of the case causes a short cycle of the slide.

Do it enough you'll know you have a cracked case the moment it hits the ground. It makes a distinct PING sound when it's cracked.

Sometimes they even split while reloading them in the press. You can tell by a slight feeling of the press lever being easier to move, and then usually the bullet wont seat and just falls into the case.

**********

This is why I wont take home brass that has been on the ground a long time and is deeply tarnished or dirty. You just don't know how long it's been exposed to the elements.

[Corbin Dallas]

Old age, over-use. It happens.

This ^^^

What headstamp?

[Corbin Dallas]

Hit it with calipers too.... I have seen 9MM fired from 40 S&W

9 out of 40 would look completely different. That 1mm difference is significant.

[WartHog]

This ^^^

What headstamp?

Win

[SandDiegoDuner]

[tabascoz28]

Starting a poll elsewhere but would you rather have cheap ammo or long lasting brass. I've had them crack on the 1st reload from different brands. Win has been an issue for me in being too long, bad QC.

[dreyna14]

Sizing work hardens brass. Eventually it will become brittle and will crack even at conservative load pressures.

[Cowboy T]

^^ As does the pressures in the 9mm case. They're similar to .357 Magnum, and I generally see those cases splitting before the .38 Special cases do. So, 11-12 rounds out of a 9mm case sounds pretty reasonable to me, if that's indeed what split it.

Odd that it was Winchester brass, if it was new. I had an issue with Remington-Peters (R-P) .45 Colt brass splitting sometimes after maybe 3-4 reloadings. Winchester, Federal, Starline, and others didn't do that.