What happened?

[SSL]

I was shooting my Savage M12 VLP today when the report sounded strange and a cloud of smoke drifted from the bolt. This is a .243 and the load was a relatively mild load of AA2700 (weighed) under a 75-grain VMax. Third shot of several groups with the identical load after the barrel had cooled. Brass is Nosler and has been fired three times. I have used this load for quite some time in all temperatures (today was a pleasant 72 degrees) with no signs of pressure. The bolt was frozen in place and required the use of a rubber mallet to open. The missing portion of the case was welded to the extractor...almost like a brass wash. The case itself required a soaking in Kroil and a ruined cleaning rod to remove. Of course, in the process of getting the remnants of the case from the bolt-head, the extractor slid down and now I need a new spring and ball bearing! Got to do a search to find a source.
Any ideas what could have caused this? I have been reloading for more years than I care to count and have never run into this. You might notice that the gasses seem to all have been directed out the primer hole. There is no evidence of any other failure in any other part of the case.

 

[ShootDots]

The case looks nice and clean. Did you use a vibratory cleaner with either walnut or corn cob media? I saw a friend of mine have a similar problem, just not as drastic. He had some media stuck in the case which really reduced the capacity of the case and his normal load all of a sudden became a W-A-Y over-pressured load.. If it was not something like that, then I don't know..

 

[fkimble@charter.net]

May just be the angle of the pic, but the flash hole looks kind of big.

Frank

 

[mongo chicago]

Could it be a detonation from too light of a load???

 

[acloco]

Hmmm...ejector ring mark on the case head too.

Edge of primer catch the edge of the primer pocket and allowed high pressure to escape?

 

[jscore]

The case looks nice and clean. Did you use a vibratory cleaner with either walnut or corn cob media? I saw a friend of mine have a similar problem, just not as drastic. He had some media stuck in the case which really reduced the capacity of the case and his normal load all of a sudden became a W-A-Y over-pressured load.. If it was not something like that, then I don't know..

I’ve always wondered about that very scenario. Usually when I find some stuck in a .223 case.

 

[beemanjohn]

It could be that batch of powder has gone bad.

 

[pdog2225]

About 4yrs ago my shooting buddy was shooting his sav mdL 12 bvss is .243 win with 75 red tipped bullets. He then switched to 107gr loads (new). It took him 2days to get the bolt open. He had not reduced the powder charge from the 75s and was 10 grains over max! the ejector was jammed back into the bolt head so hard that it split the shank, his case looked like yours. Replaced bolt head and it is still shooting these days.

 

[DiffEQ]

PM me your address, and I'll send you a spring and ball bearing.
Otherwise, sharp shooter supply in Columbus, OH should have them.

 

[JohnKielly]

Last time I saw a case with similar damage, the owner had managed to get oil inside his case, which "modified" the burn rate of the powder.

 

[SSL]

OK, more info and replies, and thanks to all for ideas:

I do clean with corn cob media in a vibratory tumbler prior to sizing. I hand-prime and inspect for media in flash holes and etc. when wiping the brass after sizing. That's not to say I couldn't have missed one.
The flash-hole does look large and very faintly lopsided. Maybe from gas erosion?
Primer seated just under flush...if I inspected it right when priming.
Powder smells sweet, looks good and has never been in an unstable climate.
The only other "red-tipped" bullets in my drawers are all .224".
Oil is a possibility...but I have no idea how it would get inside the case.

As I mentioned...I'm at a complete loss as to the cause.

 

[Jager]

What was the load?

 

[SSL]

44 grains of AA2700. Book lists 46.5 as max. I've shot this same load for at least three years.

 

[AccelR8]

I've never experienced such a failure. I wonder what a failure due to the case head being to soft would look like and I wonder if that's a possible explanation.

 

[SSL]

A first for me too. I could better understand if there was a failure somewhere in the case body, but only the head/rim area? A real puzzler. No apparent bolt face damage either.

 

[acloco]

Looking at the pictures again, still think the primer caught the edge of the primer pocket or a slight wrinkle.

The pressure exited out the side of the primer pocket.


Need picture of the boltface please.

Need measurement of the case head - is the case wall just in front of the extractor groove bulged at all?

 

[dfrosch]

How tight or loose are the primer pockets on the rest of that lot of brass? Did you find the primer from that case?

 

[SSL]

Bolt face is clean and undamaged. Case in front of extractor groove is .473 - .4735". Other fired cases average .467". Virgin cases measure .4655" on average. Blown case runs about .001 to .002" larger than other fired cases at various matching locations between the case head web and the shoulders. No primer found. Primer seating feel for the whole batch was normal.
Will post bolt face picture if I can get a good one.

 

[Bojo]

Check your bolt head very good as well. Years ago I had a oops with a Mel 12 in 22-250.
bolt head , extracter ,spring ball ejector and ejector spring. Plus reset my barrel to the new bolt head.

 

[Fast14riot]

I've had factory ammo blow primers and cut the bolt face, never anything like that though. Primers alone are not enough to cause that. Strange. Glad you are ok.