Kaboom!

[Clusterfrack]

A setback bullet is an interesting idea. That would require less odd stuff to have happened in the reloading process. However, the recoil impulse felt heavier than a typical 134k power factor load. My gut is that it was a very heavy charge.

How many reloading for that case? I have absolutely no clue. It's range pickup brass that's been used an unknown number of times. I usually have a stock of about 15000 cases that I cycle through, and brass at matches isn't picked up. So usually my brass doesn't get used a ton of times.

I've had lots of split cases, and they have never caused a problem. I just discard them. Split cases are easy to identify because the case mouth is typically smaller than the bullet diameter, so the bullet feed step fails.

[AJLooch]

It looks a lot like when a gun fires out of battery to me. I have had a Glock 17 do this and the brass looked exactly like yours does. Plus CZ's have notoriously short chambers and the hammer can drop with the slide way out of battery and the barrel unlocked.

[Clusterfrack]

Interesting idea. I just tested a S2 and can’t get the hammer to hit the firing pin farther than 1/16” out of battery.

Also, the headstamp was almost entirely flattened smooth. That would support the idea of very high pressure.

[EricP]

A setback bullet is an interesting idea. That would require less odd stuff to have happened in the reloading process. However, the recoil impulse felt heavier than a typical 134k power factor load. My gut is that it was a very heavy charge.

I was going to suggest set back. Like you, I use a powder (Power Pistol) that makes a double charge difficult. In my incident, I remember short stroking the press and not crimping the round in that station. The shell plate cycled and ejected that round into a full bin of finished rounds. I looked for the round and measured everything on top, but missed that round. When I eventually fired that round, it felt like my hand was hit with a bat and the case was partially extracted and bulged. The gun (G19) was undamaged.

I wasn’t sure how you would have set back due to lack of neck tension when you are seating and crimping in the same station unless it was fluky out of tolerance component or something like that.

[willie]

When using mixed brass, some cases are thinner than others. Thinner cases will have less case mouth tension than thicker cases. Setback is more likely to occur with thinner cases. The op theorized that even though a double load would fill the case, a compressed charge occurred. Such most likely happened. I suggest that he experiment by double charging a case and then observe how much effort is required to seat the bullet.

[Clusterfrack]

When using mixed brass, some cases are thinner than others. Thinner cases will have less case mouth tension than thicker cases. Setback is more likely to occur with thinner cases. The op theorized that even though a double load would fill the case, a compressed charge occurred. Such most likely happened. I suggest that he experiment by double charging a case and then observe how much effort is required to seat the bullet.

Good idea. I use a U sizing die that undersizes the case so I don't think there's any lack of case tension no matter what brass.

A full double charge won't seat to chamber length even with a full press on a 1050. There's no way to get a bullet and that much powder in a 9mm case.

A 1.5x charge will seat.

I think the most likely explanation was something like a 1.5x charge that happened when I cleared a jam. The Dillon powder drop can deliver a partial charge if you short stroke it. I showed the brass to some other folks, and the consensus was heavy charge.

[willie]

You very likely arrived at the cause.

Your special size die, of course, will alleviate many problems. You do have it figured out. If we were neighbors, I would be asking your advice in many instances. Since I enjoy discussing reloading, I will point out for others a couple things. Undersized resizing dies put extra stress on brass by reducing dimensions to a greater degree. This stress work hardens brass. Then when the expander again changes dimension, the same thing occurs. Eventually split necks occur. But in this progression from a so called perfect case to a case that is becoming more and more work hardened, we encounter loss of elasticity. Neck tension can decrease with each reloading. Thinner cases, because they are being expanded to the same diameter as thick cases, are less likely to produce sufficient bullet pull or grip. One reason is that the crimp die has less "meat" to work with. Over time thinner cases when work hardened will fail sooner than thicker cases.

You are cranking out a very high volume of ammo. You have an outstanding safety record.

[Russ856]

I have a piece of brass in my right cheek currently from a 9mm case blowing out the rear of the cartridge a long time ago.

Today I cannot tell it’s there and I don’t think of it until I’m reloading or shooting. The cartridge fired and bullet left the muzzle, but the case opened at the rear sending the metal into my cheek and the blood poured. A CT scan was done and metal is in fact in there.

A decision was made to leave the metal in my cheek due to it’s tiny size and location. I not longer mess with reloading 9mm or .40 calibers. I don’t know where I failed leading to my injury, I was shooting 124gr bullets over CFE Pistol at the time, brass was range brass so possibly an overworked case? Overcharged? Who knows, I wish I knew for sure.

I’ve seen a similar thing happen on the police firing range from a factory loaded round but that guy wasn’t injured.

I still hand load a good bit of .44Mag/44spl and .38/357Mag. I’ve always been careful but today I am EXTRA careful and inspect every case closely. I look at the charge level for each cartridge visually before placing my bullets for seating. This is still my greatest hobby but because of my own bad experience I look at everything I hand load extremely close.

The amount of ammo being used by the OP is astonishing and considering that amount I’d also say his safety record is really good.

[Clusterfrack]

Thanks for revisiting this thread. I was meaning to post an update because (as the Dude is fond of saying) new shit has come to light.

I had a second Kaboom, which was clearly an out of battery ignition (pic below). No injuries, and I barely noticed it except for the oddly loud report and the FTF that followed it. These were both in the same S2, my high round count practice gun.

I emailed David at CGW and he gave me his direct line. When I explained the issue, he gave me some possibilities, most of which I was able to eliminate. The most likely is a ring of crud or lead at the chamber mouth. Visual inspection revealed a lot of crud there (embarrassing...). So, I used Kroil on a bronze brush on a drill to clean it.

No issues in 2000+ rounds since.

[mmc45414]

The most likely is a ring of crud or lead at the chamber mouth.

Thanks for the follow up. IMO this is the kind of stuff that people that do not reload seem quick to blame on the ammo and crud is crud.


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