Fired case from out of battery AR-15?

[Yankee1986]

Slow ignition? Round doesn't actually fire until the exact moment the lugs unlock?
Could contact between a proud primer and the bolt face cause ignition (doubt it)?

Just spitballing.
You dont have to be a gunsmith to understand there is really NO way for an OOBD in an AR15 with an in-spec bolt & firing pin.

 

[Varminterror]

Slow ignition? Round doesn't actually fire until the exact moment the lugs unlock?

Can’t happen. In the AR design, lugs only unlock because of sufficient port pressure driving the carrier rearward. So until a bullet passes the port, there is no force to unlock the lugs.

This kind of failure mode can only happen if the round fires without the lugs locked, but has sufficient casewall support to avoid destruction of the case at peak pressure.

 

[Nature Boy]

This kind of failure mode can only happen if the round fires without the lugs locked, but has sufficient casewall support to avoid destruction of the case at peak pressure.

OOBs are rare as it is. A failure of this nature must be really rare.

 

[Jim Watson]

Hard to understand blowing the shoulder all the way forward without at least bulging the body.

 

[243winxb]

The gun fired from a locked breech. But the action opened to soon when pressure was still high.

I would be interested in the load being used. Adjustable gas block? Suppressor in use? Barrel length. Factory gun or built from parts?

https://www.hornady.com/support/superformance-in-gas-operated-firearms

open the bolt of the gun too fast. It’s a timing issue

Port pressure was way too high and opened the action too soon. Excess powder charge.

 

[Slamfire]

I am not an expert but I know I've read that due to the design of how the firing pin works it is impossible for an AR15 to fire out of battery.

And that is what I thought, till I found enough out of battery slamfire accounts on the web, and a guy I shoot with, he was a Security Guard at a National Laboratory. The type of National Laboratory where the guards are supposed to shoot on sight anyone in certain zones! Bud saw an out of battery slamfire in a Government M4 with 223 Federal Gold medal match. They give the guards full auto M4's and Federal Gold medal match to shoot in practice and training.

What is true about the Stoner design is that the firing pin is held behind the bolt face until cam down. If the primer is sensitive enough, it will go off when the AR bolt closes and the firing pin hits the primer. Normally this would be an in battery slamfire. Bolt bounce is also real, when the carrier/bolt bounces, the lugs can/will rotate out of battery on the back bounce.

To get an out of battery slamfire in an AR mechanism, the firing pin bounces off the primer and ignites it. But, full primer ignition is somehow delayed, the bolt bounces, and full ignition starts when the lugs rotate out of battery.

I think the period from ignition to full combustion of the primer is called "dwell". Primers are not like light switches, primer cake is a mix, combustion is actually complicated, dwell has plus or minus parameters. And sometimes, an AR15 goes off out of battery.

The OP is lucky as all heck that the case head did not blow. This came from a post




I had a picture of a 30-06 round that slamfired out of battery in a M1 Garand. It took did not blow the case head, and the shoulders were moved forward like the OP's picture. In the Garand out of battery slamfire, the bolt was over accelerated and cracked the back of the receiver, similar to the damage in this picture.



this was not a slamfire, it was deteriorated Greek ball ammunition. Combustion pressures will rise with old deteriorated gunpowder. So old, deteriorated, over pressure ammunition over accelerated the bolt, which rebounded off the receiver heel. And this crack developed.

 

[Varminterror]

I’ve never seen this happen with early unlock - early unlock typically gives slightly bulged caseheads and a lot of stretch, but the shoulders are well anchored sufficiently to keep the neck and shoulder well defined. Naturally, we also see different primer effects and a lot of chewing on the case rim.

The only other thing I could think of which may cause this would be an in-battery detonation with a temporary/partial bore obstruction (wondering water in the bore? Maybe a mud plug?) which allowed the gas in front of the bullet to unlock the bolt still under high chamber pressure, but not fully unsupported at peak to rupture the case.

I’m trying to recall now - I know I’ve seen brass after an AR was fired underwater, but I can’t recall it’s appearance.

 

[denton]

AR15s can and do fire out of battery. Since the firing pin is floating, a small piece of grit can lodge it forward. The result is exactly as Slamfire's photo. It is pretty rare, but it does happen. The forward portion of the case is in the chamber, and gets pressure formed to the chamber dimensions. The case head, however, is unsupported and it expands and blows out. Somewhere around here, I have an image like Slamfire's. The OP's photo does not look like that.

 

[Varminterror]

I’d certainly be tearing down and checking my FP, FP bore through the bolt (for stacked pieces of pierced primers), and my lugs.

If the rifle doubled, for any reason, that’s also sufficient reason for me to tear down and investigate.

 

[BreechFace]

AR15s can and do fire out of battery. Since the firing pin is floating, a small piece of grit can lodge it forward. The result is exactly as Slamfire's photo. It is pretty rare, but it does happen. The forward portion of the case is in the chamber, and gets pressure formed to the chamber dimensions. The case head, however, is unsupported and it expands and blows out. Somewhere around here, I have an image like Slamfire's. The OP's photo does not look like that.

With an in spec firing pin and bolt what you are suggesting can’t happen. Even with grit in the firing pin channel holding the pin in protrusion from the bolt face, once the bolt unlocks the firing pin is not long enough to protrude so it would be an in battery detonation.

What @Slamfire posts about is heading down the better path as to what is the cause, insufficient dwell time/delayed full combustion of the primer/powder getting the bolt to unlock and then reaching peak pressure causing a slight OOB.

As was stated, I would be checking all components out to see what is going on, because that is not supposed to happen in the Stoner design. Obviously, there are reports of it happening, but without checking specs on components there is no way of knowing what is the cause.

 

[243winxb]

If OP is stilll loading Accurate 2230 powder, may be a clue. https://www.thehighroad.org/index.php?threads/has-aa2230-changed-over-the-years.868606/

Double based ball powders need a magnum powder. A fmj bullet may produce less pressure because of less bearing surface. Neck tension may be an issue, if bullet moved at primer firing.

Port pressure was way too high and opened the action too soon. Excess powder charge.

higher pressure at the gas port. This can be a delayed or longer pressure curve caused by a slow burning powder. A faster burning rate powder will have a higher pressure spike earlier in the burn and then diminish as the bullet goes down the barrel. When using a slower burning rate powder, the duration of the burn is longer (in time), so when the bullet gets down to the gas port the pressure is actually higher than it was with a fast burning powder."

 

[BreechFace]

Some things I would be investigating that could potentially cause an OOB in an AR15:

-Bolt tail damaged, reduced in length; but would also need the firing pin retaining pin to be damaged or missing.
-Proud primer in which the bolt face detonated it, unlikely due to the nature of primer design and needing to be fully seated in the pocket
-Something on the bolt face, mashed primer from previous cartridge, etc., contacting primer of chambered round while still unlocked.
-broken cam pin?

 

[GW Staar]

I find this thread interesting. I've never had anything like that happen in my AR-15.....but I did have a doubling in my Remington R25, an AR10 clone, with reloads found to have 3 primers proud, caused by using really old LC brass that was so hard the swager sheared rather than swaged, and left a sliver of brass in the bottom of the primer pocket, thus preventing the primers to be seated flush, let alone, below flush!

There was no damage to the case....just one double tap, that in that caliber certainly got my attention, and so stopped shooting and started investigating. Obviously it wasn't out of battery, and after seeing what happened to the O.P.'s small .223 case, was very glad such didn't happen in the .308-sized AR. Result might have been a lot worse!

 

[Jeremy2171]

this was not a slamfire, it was deteriorated Greek ball ammunition. Combustion pressures will rise with old deteriorated gunpowder. So old, deteriorated, over pressure ammunition over accelerated the bolt, which rebounded off the receiver heel. And this crack developed.

As gunpowder deteriorates it gets weaker not stronger since the stabilizers are gone and the acids now consume the gunpowder.

These acids will leech out and "burn" holes in the brass cases. At this point the gunpowder doesn't have the same chemical energy and is woefully underpowered.

I salvaged some 1918 dated gunpowder from cases that were deteriorating. The rounds went more "poof" than bang. Low velocity and the bolt didn't barely move.

 

[Slamfire]

As gunpowder deteriorates it gets weaker not stronger since the stabilizers are gone and the acids now consume the gunpowder..

I remember your test of one old cartridge, where you did not blow yourself up. Your test was not particularly exhaustive as all you measured was velocity, you had no idea of pressures. But, I suggest you write your test and results on the back of a 3 X 5 inch index card and send it off to the next Insensitive Munitions Symposium and present the results of your test, and your conclusions. I am sure such a ground breaking test and conclusion will be highlighted in the next meeting bulletin. I don’t see an announcement for a 2023 symposium, but I am sure another will be scheduled in the near future.

2021 Insensitive Munitions & Energetic Materials (IMEM) Technology Symposium

https://www.ndia.org/events/2021/4/7/imem-technology-symposium#

Now in so far as your one off test, how about making your test slightly more rigorous? . There are a number of known unknowns that I have about deteriorated gunpowder. One of which, the level of deterioration it takes for gunpowder to detonate, and the number of tries. Since neither of us have the test equipment to determine percentage of stabilizer left, I am going to suggest to you doing a test with severely deteriorated gunpowder.

To whit, instead of shooting one round with old gunpowder, how about segregating about 150 old rifle rounds. Pick your caliber, but it would be fun to see how your Garand handles this. Shoot at least ten rounds over a chronograph and record the velocity. This is for a base line.

Then disassemble the rest of the rounds, but take an average powder charge weight from ten rounds, to use later . Put the gunpowder in a clear glass container and stopper it. Put the container in a toaster oven at 165 F (ish) and monitor the days it takes for the gunpowder to fume. And then, go a couple days after that to deplete as much of the stabilizer in the gunpowder. I don’t know when all stabilizer is depleted, so age the gunpowder past first fuming. And don’t sniff the stuff!

Then, load up the disassembled cases with this deteriorated gunpowder, charge the cartridges with the original powder charge, and as soon as possible, go to the range with your chronograph. You know, as I know, deteriorated gunpowder is outgassing corrosive gas, so limit the time of exposure to maintain case integrity. Shoot all the rounds noting the velocity and whether you encounter any pressure indications.

I don’t know what will happen. This is also, only 100 rounds. Is a 1 in a 100 statistically significant? Be interesting to find out if something happens in one hundred rounds. You believe it will be a big nothing burger because you have this “fizz theory” about gunpowder. That is, gunpowder in the case loses its fizz like soda in a bottle. I think your fizz theory is wrong. How about a more comprehensive test?

 

[Charlie98]

Yet another reason to use an AFG instead of gripping the magwell when operating operationally

After experiencing some case head ruptures in my M1a... and blowing the magazine guts out... I don't mag-grip any longer.


I can't really opine on the OP's instance... but based on the very little I've seen, I'd be checking the BCG parts, particularly the bolt lugs, and the barrel extension. Friend of mine... is AR sheared 3 lugs. A chunk of one of the lugs was left in the barrel extension, so the next round 'almost' chambered fully before the bolt wedged short of full battery. Thankfully, it did not fire.

 

[Laphroaig]

I had a OOB in an AR15 when I was single loading and dropped the bolt. I'm pretty sure it was caused by a high primer. The case separated in the chamber but the top came out when I tried to chamber the next round. The disturbing part was that my POI changed about 4 MOA to the right, so something must have bent. I shot the rifle the rest of that HP season, then replaced the A2 upper with a flat-top.

I don't see why an AR15 would be any different than any other semi with a floating firing pin.

ETA: The OP suspects a high primer and states that he loaded that ammo on a 1050. My incident occurred in my early experience with a 550C. IMO the weak link in the Dillons is the on press priming system, especially when loading decrimped military brass. I now check my finished rounds to be sure the primers are flush or slightly below.

 

[Shrinkmd]

Load is 24.5 gr of 2230, recent manufacture, 2020 or 2021 I gotta check the bottle. Hornady 55 FMJ. Stock BCM Mid 16, no modifications or anything funky. Vanilla load shooting vanilla bullets in a vanilla rifle. I have my powder check, so I doubt it was a significantly increased charge, although still possible. Every now and then I measure a 24.8 or so, but still well below the max for 223 loads, and 556 loads go higher with AA2230 powder. Using the winchester #41 primers. And the rifle was functioning perfectly fine for another 20 or 40 rounds afterward, no other issues...same load and brass, then some of my older range 1x fired, otherwise same load.

 

[BreechFace]

I don't see why an AR15 would be any different than any other semi with a floating firing pin.

A properly spec'd AR15 the firing pin is not long enough to protrude until the bolt is cammed back into the carrier and in locked position in the barrel extension. This design was on purpose for this exact reason. Different design than other semi-autos with floating pins.

 

[Charlie98]

And the rifle was functioning perfectly fine for another 20 or 40 rounds afterward, no other issues

That's the compelling factor on why I didn't really offer an opinion. If you would have sheared lugs, you would have likely encountered the same problem going forward. Sounds like an anomaly, but everything happens for a reason.

 

[BreechFace]

The cycling of a properly spec'd AR15 is as such:

With a round chambered and fired:
-Primer ignites powder charge, cartridge pressure raises and expands the cartridge to the chamber creating a gas seal
-The pressure is held and the case pushes backwards against the bolt face
-Gas flows down the barrel with the projectile reaching the gas port and gas is siphoned off and returns through the gas tube to the gas key; pressure is still fairly high in the barrel until the projectile leaves the muzzle

-The siphoned gas reaching the gas key on the carrier heads down into the expansion chamber (this is why some say the AR15 isn't a true "direct impingement," as it has an expansion chamber acting as a piston of sorts) behind the bolt, this provides two-way force one moving the carrier rearward and one moving the bolt towards the muzzle; at this point the gas on each side of the bolt face are nearly the same (or should be close with a properly gassed system); which allows a dwell time for the bolt lugs to be in a neutral position to start to unlock and start the extraction process while clearing the barrel extension.
-The carrier has resistance that is adjustable in it's path rearward in the buffer spring and buffer weights​

-Once the projectile uncorks from the muzzle the gas now has a path of lessor resistance; out the end of the barrel also causing the pressure to drop allowing the case in the chamber to reduce in size (timing of gas operation, dwell time, etc is important for this fact)
-The carrier as it heads rearward the cam pin has to follow the path starting the unlocking process and beginning the extracting and ejection

-As the carrier reaches the back of the cycle (the bolt is in the forward position with no possibility for firing pin protrusion) and starts to head forward, it strips a round off the top of the magazine (bolt is completely in the forward position, firing pin cannot protrude due to it's length not being sufficient) pushes the cartridge into the chamber, bolt hits the breechface and extractor engages the cartridge base and the force of the bolt hitting the breech starts the camming operation where the bolt locks into the barrel extension, at this point with the bolt retracting into the carrier and turning the lugs into the chamber extension, only then is the firing pin long enough to engage the primer at a force enough to ignite.

The AR15 is a floating firing pin system, but the pin's inertial energy (which is the only energy it has until in battery and the hammer smacks it from behind) is not sufficient enough to ignite primers designed for autoloading rifles. This inertial energy only comes to play when the bolt face smacks the breech causing the firing pin to stay in motion (free floating) which will impact the primer but with not enough force to do anything but leave a mark.

Well what about something sticking the firing pin in a forward position? Well that doesn’t matter either as the firing pin is only long enough to protrude at the point when the bolt is in battery.

All of this and more is why Eugene Stoner was a genius when it comes to small arms, and is why despite having millions and millions of Stoner design rifles fielded (both militarily and privately) since the Vietnam war have we not encountered but few rare cases of OOB which due to the nature of the design and safeties built into the process has to be something a miss with specs or failure of some components of the rifle or cartridge.

 

[Jeremy2171]

I remember your test of one old cartridge, where you did not blow yourself up. Your test was not particularly exhaustive as all you measured was velocity, you had no idea of pressures. But, I suggest you write your test and results on the back of a 3 X 5 inch index card and send it off to the next Insensitive Munitions Symposium and present the results of your test, and your conclusions. I am sure such a ground breaking test and conclusion will be highlighted in the next meeting bulletin. I don’t see an announcement for a 2023 symposium, but I am sure another will be scheduled in the near future.

2021 Insensitive Munitions & Energetic Materials (IMEM) Technology Symposium

https://www.ndia.org/events/2021/4/7/imem-technology-symposium#

Now in so far as your one off test, how about making your test slightly more rigorous? . There are a number of known unknowns that I have about deteriorated gunpowder. One of which, the level of deterioration it takes for gunpowder to detonate, and the number of tries. Since neither of us have the test equipment to determine percentage of stabilizer left, I am going to suggest to you doing a test with severely deteriorated gunpowder.

To whit, instead of shooting one round with old gunpowder, how about segregating about 150 old rifle rounds. Pick your caliber, but it would be fun to see how your Garand handles this. Shoot at least ten rounds over a chronograph and record the velocity. This is for a base line.

Then disassemble the rest of the rounds, but take an average powder charge weight from ten rounds, to use later . Put the gunpowder in a clear glass container and stopper it. Put the container in a toaster oven at 165 F (ish) and monitor the days it takes for the gunpowder to fume. And then, go a couple days after that to deplete as much of the stabilizer in the gunpowder. I don’t know when all stabilizer is depleted, so age the gunpowder past first fuming. And don’t sniff the stuff!

Then, load up the disassembled cases with this deteriorated gunpowder, charge the cartridges with the original powder charge, and as soon as possible, go to the range with your chronograph. You know, as I know, deteriorated gunpowder is outgassing corrosive gas, so limit the time of exposure to maintain case integrity. Shoot all the rounds noting the velocity and whether you encounter any pressure indications.

I don’t know what will happen. This is also, only 100 rounds. Is a 1 in a 100 statistically significant? Be interesting to find out if something happens in one hundred rounds. You believe it will be a big nothing burger because you have this “fizz theory” about gunpowder. That is, gunpowder in the case loses its fizz like soda in a bottle. I think your fizz theory is wrong. How about a more comprehensive test?

No reason to do all this when it's common knowledge that as gunpowder deteriorates it becomes weaker. Have you ever consulted with a ballistician? Maybe you should.....because you are causing lots of confusion to new shooters with your postings.

It's almost like you have these posts saved in another location and you literally cut and paste them in any thread where there is a reported ammo issue...regardless of whether your "pasting" is directly related to the OPs topic.

 

[Varminterror]

I don't see why an AR15 would be any different than any other semi with a floating firing pin.

Because the bolt and carrier are not fixed length. The firing pin is affixed within the carrier, and until the bolt cams into place, inherently also locking behind the barrel extension lugs, the FP should not be long enough to reach through the bolt to contact the primer.

But what “should” happen doesn’t always happen. Broken firing pins, broken cam pins, broken lugs, high set primers, stacked up discs from pierced primers in the FP bore… all kinds of odd stuff happens when we put millions of actions into the wild.

 

[Laphroaig]

I don't know, other than I had an OOB discharge with a high primer. The separated case and permanent POI change suggests to me that it was OOB.

We've all seen the little dimple on the primer with a chambered, but unfired, round. CCI 41's are made for a reason.

 

[243winxb]

Port pressure was way too high and opened the action too soon.

The soft annealed brass could easly expand @ 15,000 PSI when the action opened to soon.

Olin- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened.