I was competing in a DMR match today and using my 54R handloads for the first time and had a catastrophic failure. It appears there was an overpressure issue, causing the unsupported portion of the casehead to blowout and blow off the top cover. There were no brass shavings left in the receiver, FCG or magazine and the mangled case lost very little weight compared to other fired brass from today leading me to believe the round was fully seated and not an OOB. Another thing leading me to believe it wasn't an OOB is this is a KBI SVD with the actual safety sear legally in place. This locks the disconnector in place and does not allow for the hammer to be loosed until the bolt carrier trips the sear after moving into battery.

The load. I've fired nearly 100rds with the below powder, primer and bullet during OCW load development, though with different charge weights obviously, and had no issues. The only adjusted component from the load development to today was the once fired case. I had a bag of virgin PPU brass I used during load development and had no issues.

once fired PPU 7.62x54R brass
Lapua D166 3.105" 200gr FMJBT
Winchester Large Rifle primer seated well below flush
42.8gr IMR4064 measured with an RCBS Chargemaster
OAL: 3.000"

The brass was resized with Lee dies and their .307" sizing mandrel. The brass was incorrectly resized with the .309" mandrel first, but I lubed, resized and trimmed all cases with the .307" mandrel in place after finding almost no neck tension with the .309" mandrel sized brass. All rounds received a crimp from the Lee FCD into the cannelure on the D166 bullet.

Possible causes I can think of:

1. Too much powder. A double charge is impossible with this powder and case. The below picture shows the absolute max which will fit in the case, making a double charge an impossibility. The RCBS Chargemaster was calibrated with the provided chaeck weights prior to loading and the 6 other rounds fired in the stage before the failure did not have any excessive recoil or other issue.

2. Bullet somehow setback in the case, causing pressures to spike. I can push down on the tip of a bullet and there is zero movement after resizing the brass with the .307" mandrel and crimping into the cannelure. I also think this would have been odd since the only way I can see the round being compressed by the recoil spring would be while still in the magazine and somehow nosing down. This makes me think it wouldn't have ended up cycling and would have caused the bolt to be locked to the rear, hung up on the jammed round.

3. Casehead failure. This was once fired brass, so I don't believe there was a metallurgical defect with the case. The brass was full length resized and trimmed, though I did not do the "scratch test" with a bent paperclip on the inside of the case due to them having been fired only once. I will check the other cases I have and see if there are any with incipient casehead separation signs. Also, most photos I see of casehead seperation shows a split piece of brass, not a blownout casehead area and mangled brass.

So, what could it have been? I'm sending the rifle to a very qualified gunsmith to be checked over and get the cosmetic damage to the top cover mended. No personal harm done; just a bruised ego and some twisted dust cover sheet metal.

Top cover







The case:









Two other cases fired in that same magazine: Note the minor weight differences between them and the mangled case. This leads me to believe it was an OOB as it wasn't completely flower petaled out with some of the case material being blown into the action and magazine.





A full case of powder, making a double charge impossible.

Did you hand charge each case and weigh each charge?
Was the barrel clear after this?

What method did you use to clean the brass?

The Jesus factor.

Defective case? That's all I can come up with from the info given. Your load is well within safe limits according to the data I have. I hope you get it figured out.

Is there any chance that the case OAL was too long? That would do it but most milsurp chambers are much deeper than they need to be.

Added:

Your COAL seems a little long but every bullet is different and I have never used those. Again, most milsurp throats are real deep too but you don't know until you measure your "contact length"

Plug that scale into a RCBS power trickler and weigh each charge for your $4000 rifle!

Did you fire any rounds prior to the failure?  What does the case head look like?  Was the OAL 3.000 or 3.105"?
 

The Chargemaster is a powered trickler. It's the scale in the pictures.

Each charge was dispensed and then poured into the case before immediately seating a bullet.

4 rounds fired prior to the failure. Based on what I and others heard it sounded like two more rounds "bump fired" after the failed round, likely from me being startled and having the rifle loosely shouldered. The FCG is fully functioning still so I don't think there was a failure in that regard.

The barrel was clear as the two additional rounds fired and no issues appeared.

I dry tumble, but use a universal decapping die to ensure the flash holes are clear.

I used the Hornady bullet seating tool to determine when the rounds would contact the rifling and I'm within limits. I don't think you can make a round that's too long and still fit in the mag.

Well this is why I don't reload PPU brass. Not saying it is the problem, but I like a beefier web. That's a nice radius in that Hornady.

PPU top
LC middle
Hornady bottom

 

No additives used; just plan ol' corn cob in a vibratory tumbler to remove dirt and again after sizing to remove lube.

Yeah, I didn't think that'd be it.

Camera is too old to get good pics of the case neck with enough detail to see the cannelure with brass crimped into it.

From the split in the brass, and the flap of brass pushed out to the side in the red box, and the complete mangling of the front portion of the brass, I can't imagine this damage happened inside a chamber. The only explanation I can come up with is maybe the firing pin was stuck and the round was fired when it was chambered to the split/ring depth, and the unsupported brass let the case get mangled. It could also explain the bump fire effect you had.
In my former life I taught people to shoot, and I've seen failures that peeled back M-16 uppers like a banana, and broken M-60 bolts. The only brass I've seen that wasn't a simple case head separation was when the M-60 fired out of battery, and  that one still left part of the brass in the chamber with the head portion peeled off. I just can't picture how a round going off in battery would end up so un-chamber shaped.

But I have been wrong before.

 

I would say definately out of battery explosion.

Taken from Sgtmack122 's post:
The only explanation I can come up with is maybe the firing pin was stuck and the round was fired when it was chambered

I was thinking the same thing. This is not an uncommon occurrence but most seem to happen to mulsurps like the SKS due to cosmoline in the bolt.

I had a tiny shard / sliver of brass get into the firing pin hole of my P89 Ruger one time that stopped it from firing. Even after manual cocking and trying 2 more times.

Could be something like this caused the pin to be stuck sticking out.

Thought maybe something, liquid and/or solid may have dried in a case laying on its side allowing a clear path to the primer but taking up enough case volume to cause high pressure.

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CDNN sold most of the 308W version. They had a recall on them to have a spring put in the bolt to go over the firing pin so this exact thing does not happen. Does yours have the spring in the bolt for the pin?

Maybe they were not bump fired. Maybe after the first one the stuck firing pin was pushed back a little and then a little more until the rifle quit slam firing.

Negative, no spring on the firing pin.

The NDM-86s in .308 had issues with soft match primers and with that in mind I specifically used Winchester LR primers, but even they may not have been tough enough for the firing pin, even set well below flush.

This is absolutely possible. The other shooters and I all "think" we heard a large concussion, then bang, bang which both sounded like the previously fired shots that were on target. This is what lead us to think it was either an OOB or over pressure round in the chamber and then two bump fired rounds. Additionally, the two pieces of brass recovered were likely the two rounds fired after the failure. This is my theory at least since all other rounds, when the rifle was fully shouldered and supported ejected further forward and into vegetation, making them impossible to find. I'm thinking with the rifle no longer shouldered as tightly it robbed some recoil out of the bolt carrier and these rounds ejected more softly. Just a theory though and no way to definitively say which rounds the recovered brass is from.

Exactly the reason that the spring was installed in the 308 versions. So you can't have a slam fire.

Odd things can happen when a firing pin gets stuck.

I had an overly sharp firing pin in a PSL that punctured a primer.  The escaping gas then deformed the firing pin slightly so that it jammed in the firing pin hole in the bolt face and acted as a fixed firing pin for the next round.   There was no other damage and that second round hammered it back in the hole in the bolt face far enough not to launch the next round.

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I agree with the others that the damage to that case did not occur in the chamber.

It's also obvious that while there was some significant unconfined gas, there was no where near the full SAAMI pressure of the round present when the failure occurred.  My suspicion is the round blew up on it's way into the chamber while the thinner portion of the case ahead of the web was still able to expand and vent the pressure before the pressure in the case really started to rise to truly dangerous and destructive levels.  That would account for:

a) the mechanical mangling of the case;
b) the evidence of some substantial gas loss; and
c) the absence of the serious gas cutting, brass loss and damage to the forged bits of the weapon that you'd see in a full pressure failure of the case head.  

 

Well, when it gets put back together and deemed safe by the gunsmith I'll go for the spring loaded firing pin fix just to be safe. I've had blown primers before, but have cleaned the bolt stem since. I guess the firing pin could have been damaged though and stuck in the forward position, acting like a fixed firing pin system.

It seems that AK type rifles do not like nor handle bullet setback at all. I blew up an Arsenal SLR-106FR due to setback. I know for a fact that the case mouths were not crimped because they were leftovers from a run I loaded for a bolt gun. But the path of destruction suggests it fired out of battery.








 

The damage to the mag seems it obviously blew bits and pieces downwards into it, but we didn't see the same in my situation. Only the damaged case on the ground and no brass in the action or mag.

I use the NATO spec CCI primer I think its  #34, for my MAS 49-56. It has a reputation for slam firing. There is a firing pin mod for it too that uses a spring. My rifle does not have the mod but so far I have not had any problems using the #34s.

I think I'm going to do a spring mod to the firing pin as well. The NDM-86s in .308 needed it for anything other than surplus so this might be in the same category.