What can cause a case to blow out?

[NicVerAZ]

I had a case blowout, no biggie, it blew off the safety levers and locked the barrel, but once the case was out, the pistol appears to be fine (I will take it to the smith for inspection before shooting it again). I only need one new lever.

Data:

Berry's 124gr FN

HP-38 4.4gr

Once-fired F.C. case

1.055 OAL

STI GP6

I have since taken apart the entire batch. I have raised the OAL to 1.065 and reset the crimping die by starting to the top then 1/6 of a turn until the cartridge would drop check, then one more 1/6 of a turn.

I have also a batch ready with 4.2gr this time and made sure I was visually checking the powder charge visually. I sampled about every 12 or 15 rounds and my charges were consistant -.1/+.1gr.

I was very thorough during the initial load. I had a first batch with 4.1gr through and it worked fine.

On the third round of the batch with 4.4gr, I had the blowout.

So what could be causing this?

I will post a photo tonight.

[mizer67]

Your OAL is very short for 9mm, even with a flat point bullet, and even moreso if your bullet is the hollow base flat nose, as that bullet is much longer. Short OALs in a small case spike pressure drastically (or short-ish OALs and long bullets), particularly with faster powders like HP-38.

Also, what's your crimp measure at the case mouth? For 9mm you should be at ~.377" +/- .001" or so.

My guess is that you either had an overpressure load due to the short OAL, or that you had some setback during chambering that further shortened the OAL, or a combination of both.

Edited April 2, 2012 by mizer67

[Graham Smith]

Might have been a worn out case. Possibly a hairline split that you didn't see.

[NicVerAZ]

Berry does advise between 1.05 and 1.07.... I read plenty of threads before loading this bullet.

I now am loading at 1.065ish instead.

I will measure tonight and report.

[bikerburgess]

so many variables its hard to give a definite answer. some of the more likely are, over charged load, bullet set back, bad case. my guess would be either a bad case (I've had 3 of these in 40sw from sub gun fired brass)or a over charge (all the others can be correct it only takes 1 messed up round to ruin the party).

Mike

[NicVerAZ]

Thanks. I do not believe I will be able to find out why exactly it happened.

Instead I have to concentrate on not making it happen again. Which means getting the right OAL, not over crimping, checking all my charges visually, inspecting my brass before and after.

[Hi-Power Jack]

I had a case blowout I will post a photo tonight.

Photo and more description of what exactly happened, and what

the gun/case looked like after the incident, would be helpful.

Look forward to the photo tonight.

[NicVerAZ]

As promised, some photos.

First, the case. I have it now glued to my Dillon 550, as a constant reminder of what a screwup can cause. It also doubles as a handy pinholder, when I scoop my first powder charges and then weigh them while I adjust or sample mid-reload.

Berry's told me that my previous OAL was too small. I followed the new instructions. And I have started dismantling the remaining ammo.

Next, the pistol.

[outerlimits]

Put pistol powder in rifle cases

[NicVerAZ]

The gases simply found their way out through the weakest part: the safety levers. I could not find the right side lever. STI is sending me new levers.

The barrel is still intact. I will take the pistol to the smith before firing it.

Yup, it all looks fine...

So, basically, it was not really catastrophic. I have promised these photos to STI as well. I am pretty confident it survived to shoot another day.

[superdude]

WOW! i think that qualifies as catastrophic case failure!

the extreme bulging just ahead of the extractor groove in what's left of that region almost makes it look like a firing out of battery situation. but given the extreme pressure required for that type of failure it's a little tough to say for sure. maybe someone who has seen more of these types of failures can provide a better answer.

[NicVerAZ]

WOW! i think that qualifies as catastrophic case failure!

the extreme bulging just ahead of the extractor groove in what's left of that region almost makes it look like a firing out of battery situation. but given the extreme pressure required for that type of failure it's a little tough to say for sure. maybe someone who has seen more of these types of failures can provide a better answer.

Or... It started to push out of battery just before it ruptured.

I am pretty convinced it is a bullet seated too deep.

The bullet did hit bullseye. I was starting to enjoy shooting this batch.

[Too_Slow]

What was the Head stamp on that brass? Looking at the pictures it looks like that brass is the old style (and I do mean old as in not used anymore) "Balloon Head" type case. Other than that it looks like an "Out of Battery" detonation, I have seen several.

Brian

[NicVerAZ]

Federal. The bulge is when the brass ruptured and the gases pushed in the wrong direction, stopping recoil. Pressure built on the opposite side of the gash, hence the bulge, while the case was out by only about 1/16"

I believe the case ruptured at the level of the feed ramp on the barrel because that part of the frame shows minute scratch marks. When I released the magazine, the bits of brass fell off right away.

It could have been much worse. Here is a warning against bad OAL measurement.