Out Of Battery Detonation AR

[wildcatter]

A friend was reloading a 7mm TCU and grabbed the wrong cannister of powder. 2400 instead of IMR 4198. He did manage to stretch the frame of his Tompson Center Contender.

That don't take much! I've stretched more than one Contender! One just using factory Hornaday 260 grain SP's. Another with full house loads in 35 Remington using 210 gr. Cast Bullets and 3031 powder, " a few hundred loads in that one".

This is irrelevant to the pressures displayed in the OP's case! That is severe pressure! Sorry but brass did not flow that deep into the ejector without outrageous pressure! And even with the amount of pressure it would take to flow that much brass into the ejector, it would have to be contained with the bolt locked!

The blow out could be weak case if it were not for the obvious!

1) Flow into the ejector

2) the neck was contained till pressure dropped

3) even the shoulder was not released to deform it

In this case it looks like the case itself was contained and expanded to tight to the chamber to extract, the pressure "apparently" once high enough to actuate the action, blew the back of the case out instantly dumping its pressure while already taking out the components the system uses to activate the bolt release.

By then everything was released out the back of the case, before the bolt could contain it Long enough to hold enough pressure against the inside of the case head to start the case backwards out of the chamber.

I state this because unfortunatly decades ago, when the 788 Remington was introduced as the first rifle to ever be built on the then Commercialy adopted 7mm/08 case, I had one of the first! Same year they quit offering anything but the 223 and 22/250 with full length barrels. Everything else from 223 to 308 were only available with 18.5" carbine barrels.

I also only bought it for cast bullets! Everything was great using a 175 grain cast GC, and 2400 powder, loaded to around 2200 fps. But one case with my load of the faster 2400 powder double charged, did exactly what I see hear!

Being a bolt action, that can only fire with the bolt completely locked, as hear. Once the brass blew out in the rear, taking out the extractor, the front ring around the case head on the bolt, and dumped everything else out the pressure port in the side of the action. I had to use a hammer to beat the bolt open, yes a rawhide hammer didn't move it! But the brass head tore loose from the orfaces "ejector hole and anything else brass could flow into" while beating the bolt back as then had to tread a lag screw into the case and use a slide hammer I made to get the case out.

There was so much pressure, it formed the case to the neck and chamber, leaving it perfectly formed to the barrels chamber.

I'm confident the same thing happend here. Maybe not an over charge, maybe a heavier bullet got mixed in, this would easily be done with bulk bullets, even a single box of premium bullets, hopefully not other components left around a loading station. For me it was an eye opener, hopefully here to.

But there is little doubt in my mind, the action had to be lo ked long enough to hold enough extreme pressure to build to allow that head to flow that much brass into the ejector. Unsupported, I don't believe it would happen. Only other thing I could imagine is a very hot load, holding the action closed from dirty or failed gas system? I just can't see this much brass flow with an unsupported case head!

 

[dellet]

There is a lot still on table for possible causes. Not trying to pick on @writerman but something else that sticks out in his loading/storage method. That’s my handy work in the photo I posted. I have no room to talk but do have actual experience making mistakes.

This was all the same powder, no question. I load one powder, throw them into one bag, and mark the specs

if the rounds were loaded into boxes, they would be shot more or less in the order assembled. In a case like this you could narrow down some potential problems.

If you weigh the next 5 rounds and one is 3 grains lighter than the others, pull the bullet and check the charge. If there is a light one, good chance there will be a heavy one. Possibly one that blew up.

Might even be able to see a difference in the look of the powder suggesting wrong powder.

Just because this was the 51st shot, doesn’t mean it wasn’t the first loaded, the most likely to have the wrong powder. It was just a random round out of the bag.

In my case in the photo I posted above, the very next round would have been a squib. Had I shot them in the opposite order, it could have got real interesting to have an overcharged load and an obstruction.

True cause here may never be known, but first thing I would do is weigh the rest of the cartridges looking for anomalies.

Barrel extensions are not made to hold pressure or high pressure hammering. Neither are carriers for that matter. Back to the photo, enough gas pressure applied to the carrier and it was easier to twist the carrier around the bolt and spin in the upper, than it was to unlock the bolt. Just one more clue that in my case the bolt was definitely locked in full battery position.

 

[762willdo]

Show me a picture of the cam pin please…..

 

[drop_point]

Considering that the rest of the rounds were fine, I don't think that was the problem. I am careful. Always trim, always measure. It's very hard to overload a .223.

Actually it’s not hard at all.

 

[drop_point]

What else could it be? Fifty rounds fine, at fifty one, pulled the trigger and bam! Not a case of squibb load or overloading, or slam fire.

Over-pressure. If it fire when you pulled the trigger it wasn’t out of battery.

 

[Bojo]

Going to take a guess that upon chambering , the bullet was shoved back into the case and the case mouth severely deformed. Bolt fully closed and Kablamy took place.

If op can rule out almost all other causation, it is an option.

 

[Webster]

I had an out of battery detonation, brought the destroyed .223 AR to one of the best gunsmiths in town, and he just shook his head and said he thought it might have been 'something about the round the gun didn't like.' I reloaded 100 rounds, same everything, no variation in that box at all. 50 went through perfectly, no squibb either, and then number 51 boom! Here's a pic of the round. The dent marks are from trying to get it out of the barrel extention. The magazine was blown open, the upper cracked, the bolt end split, the lower slightly bent/may be salvageable, the barrel extention cracked, the bolt catch split, not much was not affected. Has anyone had this happen before? First time in fifty years of shooting, most times every week. I need to know what happened. Maybe someone has had this experience before.

Is it possible you had a bullet or some obstruction in the barrel? Look in the barrel and let us know if there is a bullet or maybe a cleaning patch in the barrel. After I clean my barrel I always look down the barrel for a stuck patch.

 

[jelenko]

he action had to be lo closed long enough to hold enough extreme pressure to build to allow that head to flow that much brass into the ejector.

This

 

[Webster]

More pictures please
View attachment 1542157
Brass flowed deep into ejector hole?
Flat primer still below flush with crater?
Extractor pulled the case rim off and case blew out?
Bolt is trash, right? Broken lugs?
Too much gas and over pressure?
Caliber, headstamp, and gas port size?
Missed the .223 in the first post.
Looks like some of the case damage was from pulling the blown case out.

Below the primer is that a large piece of brass extruded into the ejector hole? Is it to big for an ejector hole? There is no other opening for the brass to get pushed into. If so I would think you would have to be well over 65,000 PSi to move the metal into the hole. My guess has to be a barrel obstructiom??? You still have the barrel check it out.

 

[DaveTooley]

To do that kind of

Below the primer is that a large piece of brass extruded into the ejector hole? Is it to big for an ejector hole? There is no other opening for the brass to get pushed into. If so I would think you would have to be well over 65,000 PSi to move the metal into the hole. My guess has to be a barrel obstructiom??? You still have the barrel check it out.

To have damage like that the pressure had to be close to 100K PSI.

 

[SecondsCount]

Over-pressure. If it fire when you pulled the trigger it wasn’t out of battery.

This.

Take a look at the mechanics of an AR-15 bolt carrier group. The firing pin cannot strike the primer if the bolt is not in battery.

 

[Kracken McGraw]

To do that kind of

To have damage like that the pressure had to be close to 100K PSI.

Is that even possible?

 

[Jon Leary]

My guess has to be a barrel obstructiom???
Sure seems like it.

 

[Webster]

To do that kind of

To have damage like that the pressure had to be close to 100K PSI.

Right on. This has to be something besides the cartridge itself.

He also stated damage to:
The magazine was blown open, the upper cracked, the bolt end split, the lower slightly bent/may be salvageable, the barrel extention cracked, the bolt catch split. Had to be an obstruction in the bore. to get this pressure level.

 

[dellet]

Is that even possible?

My photo in post #105 quickload guesstimated 130,000ish. Double charge #9

Just to get an idea I ran the op’s load and not having the particulars, the load seemed pretty mild , low 50’s. Allow 10% for a hot lot of powder and reduce case capacity one grain of water weight and the load jumped to high 70’s. Adjust starting pressure to simulate a jam and it climbed into the low to mid 80’s.

All of a sudden an odd piece of brass, over crimped on a thick neck or bullet sliding out on chambering do to low neck tension/no crimp on a thin neck and it’s not hard to come up with a scenario that led to a kaboom.

Not to mention a simple powder bridge that might have added a couple grains. I think it was around 25 grains at his length for 100% density, probably wouldn’t feel 26 grains on a single stage press with any kind of cam over.

Lots of ways it could have happened.

 

[Rocketvapor]

I've read where some high temperature treatments of bolts and extensions make them BRITTLE.
Extra pressure and that may be a contributor.
Ejector flow looks extreme, but the second pic of the case head and the primer doesn't look all that flat.
I would have expected primer to be flattened and flow out into the pocket rim.
https://forum.accurateshooter.com/attachments/round-jpg.1542632/

 

[wildcatter]

I've read where some high temperature treatments of bolts and extensions make them BRITTLE.
Extra pressure and that may be a contributor.
Ejector flow looks extreme, but the second pic of the case head and the primer doesn't look all that flat.
I would have expected primer to be flattened and flow out into the pocket rim.
https://forum.accurateshooter.com/attachments/round-jpg.1542632/

If you look it is not only flat, but rough surface is from extreme pressure, over sized is also obvious, with a crater. My 788 never blanked, but the primer, like this one was larger diameter than it started out.

Obvious, HIGH PRESSURE! A 5.56 powder capacity makes the obstruction comment a good possibility. But if this was a continuing shot, was bullet impact confirmed from the previous round? If so, what could the obstruction be on a continuous shot? Or was this just snap them off as fast as possible just to make noise?

 

[tommeboy]

if the brass is soft from a bad anneal that ejector swage would happen on a normal pressure load.

i take it that no one here is familiar with forging of metal. I have been working in the metal forging business for over 20 years. When any metalis soft it will flow. Especially if the op'er does not know the history of the brass.

I seen it here from a local shooter. He scrounged brass at a local gun range. Every year they burn off the grass. Guess where he got the brass right after they burned the grass. Two weeks later he blows his gun up exactly like this. The brass was annealed dead soft from the fire.

Case heads blow out like this all the time. It just happens. ALL of you guys are assuming that the barrel, bolt, brass, load were all in spec. And if they were this would not happen.

I take it a lot of the guys here are not that familiar with how the AR system works and it shows. I have now given you 3 things that could all leade up to what happened. I don't think he messed up the loading one bit. That 23.5 load is safe for any 556 rifle. 25.3 is max for a 223 cartridge using a 55gr bullet. A 556 can go even higher.

 

[Jeff Porter]

I am leaning toward a .243 bullet mixed in with the batch.

 

[tommeboy]

it would not chamber if there was a 243 bullet in the case. Not going to happen