Oversize flash hole/case rupture

[Dave Marshall]

Posing a question for the brain trust here.

What is the likely effect on internal pressure of an oversized flash hole in a centerfire rifle cartridge?

 

[john pruitt]

not enough to worry about that is for sure

 

[Dave Marshall]

I had a catastrophic case failure. Trying to figure out why.

 

[Bc'z]

I had a catastrophic case failure. Trying to figure out why.

Explain please

 

[Dave Marshall]

I had a brand new 6xc case fail where the rim meets the body. It ruptured completely and did some damage to the rifle and shooter. This is also the only unsupported area of the chamber. I was able to find most of the debris and all of the ruptured case. The flash hole is considerably oversized and oblong in shape. So far, the flash hole is the only thing I can see that is not normal.

 

[Bc'z]

Thanks.
Winchester brass?

 

[Dave Marshall]

No, Winchester doesn't make 6xc brass. There are only 3 manufacturers of 6xc, and I'm not going to trash any of them here.

 

[rwj]

I hope that you were not seriously injured and have fully recovered!

You stated that the case was new, is the same true for the rifle?

 

[243winxb]

https://apps.dtic.mil/docs/citations/ADA606635

Primer pocket with enlarged (flash) spit-hole (0.110 in diameter), tested.

The military test shows less pressure with the larger flash hole, if i read it correctly?.

Some brass is formed using 2 units. The case head is stamped. The body starts as a tube. They are pressed together under high pressure to form a unit. Then formed.

Some brass may fail.

 

[Dave Marshall]

I hope that you were not seriously injured and have fully recovered!

You stated that the case was new, is the same true for the rifle?

I was incredibly lucky. I have a bad habit of shooting without glasses. It's obviously not wise. The case ruptured and vented gases out the magazine well and along both sides of the bolt. The magazine was blown out and the bottom metal deformed. The extractor (sako style) was blown off and hit my cheek. The bolt catch was also blown off. I was hit with shrapnel on my cheek and just above my right eye. My eye was amazingly unharmed. INCREDIBLY lucky. It's a huge lesson for me and I hope others as well.

The rifle is not new. I had an older barrel with a smaller chamber re-chambered with a larger reamer. I fired one round with no issue and the following round blew up the rifle. I have fired over 100 pieces of the same brass without issue. The first fired case measures as expected. There were no obvious issues with chamber dimensions in the fired case.

 

[Dave Marshall]

https://apps.dtic.mil/docs/citations/ADA606635

Primer pocket with enlarged (flash) spit-hole (0.110 in diameter), tested.

The military test shows less pressure with the larger flash hole, if i read it correctly?.

Some brass is formed using 2 units. The case head is stamped. The body starts as a tube. They are pressed together under high pressure to form a unit. Then formed.

Some brass may fail.

Thanks for posting that report. I had only seen a report of testing with smaller flash holes.

This largely answers the questions.

 

[Mulligan]

I was incredibly lucky. I have a bad habit of shooting without glasses. It's obviously not wise. The case ruptured and vented gases out the magazine well and along both sides of the bolt. The magazine was blown out and the bottom metal deformed. The extractor (sako style) was blown off and hit my cheek. The bolt catch was also blown off. I was hit with shrapnel on my cheek and just above my right eye. My eye was amazingly unharmed. INCREDIBLY lucky. It's a huge lesson for me and I hope others as well.

The rifle is not new. I had an older barrel with a smaller chamber re-chambered with a larger reamer. I fired one round with no issue and the following round blew up the rifle. I have fired over 100 pieces of the same brass without issue. The first fired case measures as expected. There were no obvious issues with chamber dimensions in the fired case.

Wow!
Thanks for sharing.
Please keep us posted
CW

 

[243winxb]

Description Alpha Munition’s 6XC brass is optimized for chambers similar to 6XC II and CIP reamer spec. For the best performance we recommend a chamber diameter ranging between .4705 to .4714 at 0.200″ off the bolt face, and a neck diameter between .274 to .276.

I dont see a SAAMI standard. The 6xc is still a wildcat? Tubb desigh? Interesting.

http://www.6mmbr.com/6XC.html

 

[Rsadams]

Carbon ring..?

 

[Texas10]

Any possibility that the case was trimmed too long for the chamber, resulting in a pinched bullet? I have seen the same thing happen in the same sequence before. First round shoots normally, next round Ka-Booms. Brass head expanded out, primer blown out, bolt disassembled violently. In checking other loaded rounds in the shooters box many were found .02 and more over max length, and that particular shooter did not own case trimming tools, just chamfering tools.

Not saying you'd commit any of these sins, just exploring possibilities.

 

[GotRDid]

“Some brass is formed using 2 units. The case head is stamped. The body starts as a tube. They are pressed together under high pressure to form a unit. Then formed. “

Where can we find further info/video of such a process?
GotRDid.

 

[243winxb]

Where can we find further info/video of such a process?
GotRDid.

google patents search http://www.google.com/patents/EP2552619B1?cl=en Not saying this is/was the problem.

Brass - drawing vs extrusion. The extrusion of brass may not be the SAFEST METHOD of making brass. The cartridge case is manufactured according to the method of the invention as defined in the claim from a conventional seamed or seamless pipe, from which the final shape of a tubular section B is formed with cold forming of the pipe. Then a bottom C of the case, which had been produced by cutting, is joined with the formed pipe section B in various ways like welding, soldering, forming, pressing, etc. in order to manufacture a cartridge case. Figure 5 cartridge case in cross-section manufactured according to the method of the invention before and after placement of the bottom C of the case to the deformed pipe B. New patent 2010.

 

[Dave Marshall]

Carbon ring..?

Kicking the possibility around. If there was a ring, and the chamber was cut a couple thousandths deeper, it could constrict the case mouth in the ring.

 

[Dave Marshall]

Any possibility that the case was trimmed too long for the chamber, resulting in a pinched bullet? I have seen the same thing happen in the same sequence before. First round shoots normally, next round Ka-Booms. Brass head expanded out, primer blown out, bolt disassembled violently. In checking other loaded rounds in the shooters box many were found .02 and more over max length, and that particular shooter did not own case trimming tools, just chamfering tools.

Not saying you'd commit any of these sins, just exploring possibilities.

It is possible in a way. The cases are new, and the correct length. The neck of the chamber may be artificially short due to carbon build up. The effect would be similar to having cases that are too long.

Gunsmith will be getting a borescope in there soon. I may have him cut the barrel lengthwise for a good look too.

 

[Texas10]

Or maybe make a cast of the chamber?