Guns are dangerous. Federal AE223BK Kaboom.

[Lostinthewoods]

Then pull a bullet and see how much space is left in the case to add such a double load of powder. I doubt that there will be that much room. There will be enough room for a few more grains, but not a double.

Exactly, if you pulled a bullet from one of those rounds (IF they are truly factory Fed AE .223), they use a carefully chosen canister grade powder with a high load density. Even a full case of the factory powder would not bring pressures to OVER proof load area as this case is showing.

I've reloaded for over 35 years, started on my grandpa's kitchen table with a hammer and a LEE .38 special hand die, I was about 10 years old and he let me beat the primers in. I learned to load bottleneck cases with my dad's Lyman nutcracker type .222 REM loader. I've made some really stupid mistakes, esp. with pistol powders, and blown some stuff up. I loaded 20-30K a year back when I shot a lot of pistol. In the military and as a civvy contractor I've seen M16's with 3 bullets lodged in the barrel, cleaning rods, sticks, etc. But I have only seen a case head like that twice. Especially with the other damage signs on the firearm.

That's why I still believe that cartridge fired SOMEHOW with a gross headspace issue. Maybe .010 to .020" or so.

I wish he could get that measurement I requested. It may not be definitive, but would answer the question in my mind, anyway.

[Molon]

Originally posted by Lostinthewoods:

Exactly, if you pulled a bullet from one of those rounds (IF they are truly factory Fed AE .223), they use a carefully chosen canister grade powder with a high load density. Even a full case of the factory powder would not bring pressures to OVER proof load area as this case is showing.


That's why I still believe that cartridge fired SOMEHOW with a gross headspace issue. Maybe .010 to .020" or so.

Lot’s of erroneous information in that post. For starters Federal does not use "canister grade powders" in American Eagle and XM193 ammunition. They use commercial grade powders. Secondly, over-pressure loads well beyond proof pressures can certainly be obtained in the .223/5.56mm cartridge.

The commercial grade powders used by Federal to load XM193 are vary similar in burn rate and bulk density to canister grade H335; not exactly the same, but very similar. A virgin Lake City 5.56mm case can easily hold 31.0 grains of H335. Do you know what a typical charge weight is for XM193? A projection in QuickLoad shows that just 30.0 grains of H335 under a 55 grain FMJ bullet can generate pressures in the neighborhood of 80,000 PSI.







Here’s a link to an article on Armalite’s website showing the condition of a casehead after an over-pressure event.

http://www.armalite.com/images/Tech%...p,%2002.01.pdf



Here’s the pic of the casehead from the article.





Here's Derek Connor's pics from his kaboom. Look familiar?





Lastly, Derek Connor has already stated that the headspace issue has been ruled out. He had the head space checked and “it was fine.”

[markm]

Awesome, Molon.

That quickload is cool, A buddy runs numbers for me through it from time to time.

[Molon]

Awesome, Molon.

That quickload is cool, A buddy runs numbers for me through it from time to time.

Just keep in mind that the parameters of the program must be adjusted to match actual measured findings for it's projections to be accurate.

[Derek_Connor]

Here's Derek Connor's pics from his kaboom. Look familiar?





Lastly, Derek Connor has already stated that the headspace issue has been ruled out. He had the head space checked and “it was fine.”

Looks like the same piece of brass...


From that PDF:

A cartridge case failure allows this high pressure gas to escape into the barrel extension, where
it flows into contact with the bolt and bolt carrier. As it expands, the gas has a larger working
surface to work on than it does inside the cartridge case. This places tremendous stresses on
the bolt and carrier.
The high pressure gas bends the front end of the extractor outward, locking it behind the locking
lugs of the barrel extension. In rare cases the barrel extension may be split.

Exactly what happened to my extractor.

Now, I'll freely admit I cannot verify w/100% that there WASN"T a bore obstruction. When this event happened, it was approximately the 22-25th round of a full 30 round PMAG.

But if I would have had a "squib" - the outcome would have been severely different I'd imagine.

So with the current info, it looks like over pressure event caused by case failure..

[Todd.K]

Molon, can you show several pressure points vs powder charge?

What many don't understand it that the pressure vs powder charge spikes up as you approach/exceed max. Each grain of powder added does not increase pressure in a linear fashion.

The idea that you cannot fit enough extra powder in the case to be dangerous is a contributing factor in many new reloaders KB's as well.


One other interesting thing I found from examining a different KB was that the barrel extension was cracked. The extractor was forced out by the brass flow and expanded into the barrel extension, cracking it all the way to the shoulder.
I ONLY DISCOVERED THE CRACK AFTER THE BARREL WAS REMOVED FROM THE UPPER!

[FromMyColdDeadHand]

Cool thread. Way better than that CSI crap on TV.

[R.Miksits]

First pic, bolt in battery, completely locked, carrier seated fully forward. Firing pin can reach the primer. Since that is a fired case in the chamber, the FP in this picture is actually to its max forward position, nestled in the firing pin dent in the primer.

Second pic, bolt in battery, completely locked, carrier retracted a bit, not fully seated, but not far enough back to have started rotating and unlocking the bolt. Firing pin is blocked from contacting the primer by a step in the carrier that stops the firing pin's flange. Again-- bolt is completely locked and FP cannot touch the primer. Misses it by a long shot, by design.
28042009/20332825741.jpg[/img]

So im guessing this is why there are very light dimples on the primer when a round is chamberd but not fired?

Given the evidence ned Christiansen provided I can't see an out of battery discharge. Thank you for taking the time to do this Ned.

Rob

[FromMyColdDeadHand]

So im guessing this is why there are very light dimples on the primer when a round is chamberd but not fired?

Given the evidence ned Christiansen provided I can see an out of battery discharge. Thank you for taking the time to do this Ned.

Rob

I thought Ned's pics showed that an OOB fire is largely imposible? Light Dimples are from the intertia of the firing pin coming forward after the bolt is closed, right?

Just a general question, for the OOB theory to be correct, the gun would have had to double, correct? So you have a gun that doubled, then with an OOB occurance at the same time? That is some pretty slim odds, eh? Versus the chance of an overcharge.

[Lostinthewoods]

Lot’s of erroneous information in that post. For starters Federal does not use "canister grade powders" in American Eagle and XM193 ammunition. They use commercial grade powders. Secondly, over-pressure loads well beyond proof pressures can certainly be obtained in the .223/5.56mm cartridge.

The commercial grade powders used by Federal to load XM193 are vary similar in burn rate and bulk density to canister grade H335; not exactly the same, but very similar. A virgin Lake City 5.56mm case can easily hold 31.0 grains of H335. Do you know what a typical charge weight is for XM193? A projection in QuickLoad shows that just 30.0 grains of H335 under a 55 grain FMJ bullet can generate pressures in the neighborhood of 80,000 PSI.

Sorry I used the wrong nomenclature, the point I was making was that the powder may be SIMILAR, but it IS NOT the same as H335, so your pressure chart is just a guess.

Even if it is correct, 80K chamber pressure should NOT blow the brass like in the pic.

You are basing your pressure data on SAAMI CHAMBER pressure, not NATO spec, which is measured at the CASE MOUTH, and can make a bunch of difference in CHAMBER pressure, as much as 20K psi, if I remember correctly.

Our NORMAL 5.56 mm NATO-spec loads could average over 75,000 psi CHAMBER pressure, every time you pull the trigger.

I'd guess the Armalite pic is of a reload with the wrong powder, like Mr. Christianson's pistol powder example cited above.

Again, if the ammo shot by the OP WAS a reload, all bets are off, but if it was factory ammo, I think other factors contributed to the problem.

PITA, ain't I ?