Blown case base...looking for feedback

[pavementends]

I have seen over pressure and cases fired in the wrong chamber where the case head expanded until the head stamp was not readable and the case had to be pried off of the bolt head. I have never seen a case with 3 eqadistant splits. A photo of the whole case from the side might be helpful.

 

[Doom]

I blew it when I mentioned over annealing. After thinking about the failure though these are my thoughts/observations. The failure most likely originated in the web. Since this is Lake City I'm betting the case is actually harder than commercial cases in that area. As the brass gets harder the yield strength approaches the tensile strength so a failure of this type would be more likely to occur (it's more brittle). There are two likely scenarios that would explain this type of failure. The first is overpressure. Not knowing the specifics of the load or powder its impossible to speculate on the possibility. There is the phenomenon with slow powders and low case fill where the powder doses not burn efficiently but enough to move the bullet into the rifling then slows down or stops and the power then burns and causes a very high secondary pressure spike. The other likely scenario is an imperfection in the flash hole that creates a stress riser above that which exists for the hole itself or an oversized flash hole which seems unlikely.

Since the bolt opened easily I would really question whether overpressure of the round actually occurred. Enough pressure to split open the web would seem to imply that the case would have expanded to the point the bolt lift would be hard. That leaves the possibility of a brass imperfection or hardness issue that allowed the web to fail. Brass hardness seems unlikely as the tensile strength increases with hardness.

It's probably going to be impossible to know what happened without some detailed forensic metallurgical analysis. If I were to be forced to give an opinion I would go with a case issue.

 

[CJ6]

Range brass = $$$. I pick range brass up and sell it at the recyclers for cash.

 

[DShortt]

I blew it when I mentioned over annealing. After thinking about the failure though these are my thoughts/observations. The failure most likely originated in the web. Since this is Lake City I'm betting the case is actually harder than commercial cases in that area. As the brass gets harder the yield strength approaches the tensile strength so a failure of this type would be more likely to occur (it's more brittle). There are two likely scenarios that would explain this type of failure. The first is overpressure. Not knowing the specifics of the load or powder its impossible to speculate on the possibility. There is the phenomenon with slow powders and low case fill where the powder doses not burn efficiently but enough to move the bullet into the rifling then slows down or stops and the power then burns and causes a very high secondary pressure spike. The other likely scenario is an imperfection in the flash hole that creates a stress riser above that which exists for the hole itself or an oversized flash hole which seems unlikely.

Since the bolt opened easily I would really question whether overpressure of the round actually occurred. Enough pressure to split open the web would seem to imply that the case would have expanded to the point the bolt lift would be hard. That leaves the possibility of a brass imperfection or hardness issue that allowed the web to fail. Brass hardness seems unlikely as the tensile strength increases with hardness.

It's probably going to be impossible to know what happened without some detailed forensic metallurgical analysis. If I were to be forced to give an opinion I would go with a case issue.

Your talking about SEE there. Secondary Explosive Effect. Extremely controversial subject no one has been able to prove. Results in destroyed firearms according to the premise. Not case head damage like this.

I'm still hanging my hat on a completely unsupported case head. It would help immensely if the OP would post a side view of the case. It appears at this time we'll never get one. Consider why.

 

[Old Navy]

Your talking about SEE there. Secondary Explosive Effect. Extremely controversial subject no one has been able to prove.

Some of us are old enough to remember and I thought is was proven using reduced loads of 4831 in mag size cases. Probably goes back 40+ years ago. Still, I have never seen a case like that one.

 

[358WCF]

Going back a year or two, there was a post with a case that was all boogered up somewhat like this... maybe. Memory is a bit fuzzy with details, but it turned out the poster had the decapping stem turned in too far & was pushing the bottom of the web downward some when setting up the sizing die. Unsure if the boogered cases were fired or caught before being loaded. Maybe someone can find the thread.

Could it be something as simple as this?

 

[Rocketvapor]

I think I saw pics of that on this or another forum.
Borescope pics inside the case.

 

[DShortt]

I think I saw pics of that on this or another forum.
Borescope pics inside the case.

I've been wondering if this is a set-up.

 

[Doom]

Going back a year or two, there was a post with a case that was all boogered up somewhat like this... maybe. Memory is a bit fuzzy with details, but it turned out the poster had the decapping stem turned in too far & was pushing the bottom of the web downward some when setting up the sizing die. Unsure if the boogered cases were fired or caught before being loaded. Maybe someone can find the thread.

Could it be something as simple as this?

I haven't seen anything before showing that issue but it is a possibility.