AR15 , slam fire reasons?

[Rec1er]

AR15 , (not going to mention make) A colleague has had what I think is a slam fire, he`s vague about how it happened , he says he put the mag in and pressed the bolt release , boom, it fired out of battery and blown the plastic mag out and smashed it , he said "I think it was the Hornady 55gr training ammo I have but it may have been a home load I had lying around from years ago "
The case minus the head is still in the chamber , bore is clear but the extractor is damaged and the bolt lugs appear to have been stressed , he said he knocked out what was left of the case head with a cleaning rod when he tried to remove the case.

Your thoughts please.

 

[RTH1800]

First question is did he buy it new or used? Any trigger changes, mods?

 

[Rec1er]

Brand new AR15 ,300 rounds through it, factory not custom built .

 

[diverdon]

I'm quite happy that you are not reporting an injury to go along with this. I get that you don't want to mention the make but I wonder if this is an unmodified factory rifle.

 

[Rec1er]

Bruised foot , nothing serious , unmodified rifle.

 

[Bulletsmith]

Seen this happen with soft primers. Federal Gold medal match primers my have caused this to happen years ago. now with the Magnum and AR type primers it should not occur.

 

[GONE BAD]

I would bet the latter; an old hand load.
Added to say not properly sized (didn't chamber) and a thin cupped primer not seated deep enough.
Does he have any of the factory ammo left? Might want to send it back and have it looked at.
Glad no serious injury occured!

 

[Stooxie]

I've seen it happen when the trigger pins weren't seated properly. Can also happen with something like a JP trigger where the disconnector nose gets ground down manually. If you make it too sensitive it can drop when the BCG slams home.

-Stooxie

 

[Fig]

99.99% slam fire = booger hook

 

[sobrbiker883]

An in-spec AR with trigger pins intact will not impact firing pin by hammer until lockup.
Crap in firing pin channel or other reason firing pin would be stuck protruding would be my guess.

 

[Yondering]

I don't believe that it's a slam fire if it fired out of battery. The firing pin isn't supposed to be able to reach the primer until the bolt is at least partially locked up.

Slam fires can happen, but what you describe sounds like something else IMO, and I'm inclined to blame the ammo first, or maybe some sort of debris on the bolt face.

 

[Sogan]

99.99% slam fire = booger hook

To blow the magazine out and cause the other issues? Sounds like something else going on. Simply pulling the trigger on a round in the chamber does not cause these issues

 

[...]

he said "I think it was the Hornady 55gr training ammo I have but it may have been a home load I had lying around from years ago "

bullshit.....he knows damn well......im guessing the latter.

either he had a kaboom...or he had a proud primer that caused the out of battery discharge.

 

[Rocketvapor]

Slap, bang is sometimes operator.
I would bump rattle check the fire control group first.
It doesn't matter what ammo you use if the hammer can fall without someone pulling the trigger.
Once you have verified the rifle works as intended. Then start looking into the ammo.
You described a case separation with damage to the extractor.
If this was in fact before the trigger was pulled a high primer could be the cause. Reloaded ammo should be checked after sitting for a long while for primers working out.
"The bolt lugs appear to be stressed" means what? Corners rounded or chipped?

If you can't tell from the case remains if it was factory ammo, contact them and claim it was.
They will set you straight.

 

[jab00]

Would factory grease in the firing pin channel cause the firing pin to get stuck with the tip exposed enough to cause the slam fire?

 

[Rec1er]

To blow the magazine out and cause the other issues? Sounds like something else going on. Simply pulling the trigger on a round in the chamber does not cause these issues

I stated he did not pull the trigger , just depressed the bolt release.

 

[5pins]

Would factory grease in the firing pin channel cause the firing pin to get stuck with the tip exposed enough to cause the slam fire?

No, the firing pin is not long enough to protrude through the firing pin hole unless the bolt is locked.

 

[BravoSector1]

Slap, bang is sometimes operator.
I would bump rattle check the fire control group first.
It doesn't matter what ammo you use if the hammer can fall without someone pulling the trigger.
Once you have verified the rifle works as intended. Then start looking into the ammo.
You described a case separation with damage to the extractor.
If this was in fact before the trigger was pulled a high primer could be the cause. Reloaded ammo should be checked after sitting for a long while for primers working out.
"The bolt lugs appear to be stressed" means what? Corners rounded or chipped?

If you can't tell from the case remains if it was factory ammo, contact them and claim it was.
They will set you straight.

Trigger, actuator, error

 

[Velocity Chad]

No, the firing pin is not long enough to protrude through the firing pin hole unless the bolt is locked.

Here is the key. Doesn't matter what the hammer and trigger do unless something is out of spec. The pin can't hit the primer out of battery. It's a load issue I would bet.

 

[wade2big]

I stated he did not pull the trigger , just depressed the bolt release.

With his finger on the trigger ?. He probably has a light trigger in his AR and had his finger on it when he let the bolt drop.

 

[NukeMMC]

The pin can't hit the primer out of battery. It's a load issue I would bet.

This is the KEY concept here. A firing pin of proper length CANNOT stick in the bolt and fire a round out of battery. The fact that the lugs appeared to be "stressed" shows the bolt was, in fact, in battery! Thus you have an overpressure event that caused the bolt to be unlocked under pressure and the case head separation event caused the magazine blowout. Obstruction in the muzzle, too-slow powder with an excess charge, pistol powder instead of rifle ... the list goes on.
Lesson should be learned. Take the case out of the chamber by freezing the barrel and using a piece of tig wire with a hook at the end to pull it out. Brass shrinks about 40% more than steel for a given temperature change. New bolt, check headspace, scope the bore and see if you bulged the barrel, check and re-check powder and primer seating when reloading. Make damned sure you eirher use a different measure for pistol powder than rifle or empty the powder measure EVERY time.

 

[supercorndogs]

Slap, bang is sometimes operator.
I would bump rattle check the fire control group first.
It doesn't matter what ammo you use if the hammer can fall without someone pulling the trigger.
Once you have verified the rifle works as intended. Then start looking into the ammo.
You described a case separation with damage to the extractor.
If this was in fact before the trigger was pulled a high primer could be the cause. Reloaded ammo should be checked after sitting for a long while for primers working out.
"The bolt lugs appear to be stressed" means what? Corners rounded or chipped?

If you can't tell from the case remains if it was factory ammo, contact them and claim it was.
They will set you straight.

Primers do not work out over time.

 

[Rocketvapor]

Reloads, looser than normal pockets, storage temperature changes, powder gassing, and primers HAVE been know to fall out of old reloads.

 

[Sogan]

I stated he did not pull the trigger , just depressed the bolt release.

Correct. As you can tell I didn’t quote you in my response. I quoted someone who said “booger hook” which typically means trigger finger pulled the trigger.

 

[Old Man with Gun]

Was this the first round ever, had it worked before?
The straight blowback pistol caliber ARs can fire out of battery but for a DI it is quite rare.

I'd take a very hard look at the firing pin, having it sticking out because something is assembled wrong, has a burr, something in the channel, etc. Seems most likely if this was first shot of the day.

If it had worked on previous trips, was the BCG taken apart between?

 

[Velocity Chad]

Outside of the cam pin not being installed at all, what exactly could be installed wrong that would allow the firing pin to protrude from the bolt while out of battery? Beyond out of spec parts, or MAYBE a high primer. An ar is not going to fire out of battery.

 

[Old Man with Gun]

Outside of the cam pin not being installed at all, what exactly could be installed wrong that would allow the firing pin to protrude from the bolt while out of battery? Beyond out of spec parts, or MAYBE a high primer. An ar is not going to fire out of battery.

To have the kind of pressure that blows a magazine out would have to be either out of battery, way to much pressure from a bad loading or something like trying to shoot 300 blackout in a 5.56. Let's rule out the 300BO.

I don't think it fired totally out of battery, damage to lugs, extractor, seperated case implies it was at least partially locked.

Firing when dropping the bolt combined with the pressure leads me to believe the chamber was mostly closed, but not 100%. If lugs were not fully engaged could a normal powder charge do this? Probably.

Is it more likely a good round detonated slightly before full lockup or he happened to simultaneously have a catastrophicly over pressure round and a failure of the fire control group dropping the hammer.

This is why I am asking questions about first shot of the day, first shot ever and asking to inspect firing pin area.

I'm not sure if a raised primer could pop, far more likely something struck it.

If it had never been fired I would suspect something out of spec, burr, bent firing pin protruding, something.

If it had worked on previous trips I would suspect something got wedged in the firing pin hole, firing pin broke dry firing and tip stuck protruding, something keeping firing pin from free floating in the channel but forced forward.

I don't think the cam pin is missing, but could the firing pin have gotten bent, a burr repositioned, some cleaning patch, part of a Q-tip or something get left behind? Maybe.

Don't know if he has the case head, but a look at it might say a lot.

 

[Rec1er]

To have the kind of pressure that blows a magazine out would have to be either out of battery, way to much pressure from a bad loading or something like trying to shoot 300 blackout in a 5.56. Let's rule out the 300BO.

I don't think it fired totally out of battery, damage to lugs, extractor, seperated case implies it was at least partially locked.

Firing when dropping the bolt combined with the pressure leads me to believe the chamber was mostly closed, but not 100%. If lugs were not fully engaged could a normal powder charge do this? Probably.

Is it more likely a good round detonated slightly before full lockup or he happened to simultaneously have a catastrophicly over pressure round and a failure of the fire control group dropping the hammer.

This is why I am asking questions about first shot of the day, first shot ever and asking to inspect firing pin area.

I'm not sure if a raised primer could pop, far more likely something struck it.

If it had never been fired I would suspect something out of spec, burr, bent firing pin protruding, something.

If it had worked on previous trips I would suspect something got wedged in the firing pin hole, firing pin broke dry firing and tip stuck protruding, something keeping firing pin from free floating in the channel but forced forward.

I don't think the cam pin is missing, but could the firing pin have gotten bent, a burr repositioned, some cleaning patch, part of a Q-tip or something get left behind? Maybe.

Don't know if he has the case head, but a look at it might say a lot.

The rifle has only fired around 150 rounds according to him , your comment that the bolt was possibly mostly but not completely closed makes sense having looked at the bolt , extractor damaged and bolt luggs marked , the rifle is only a few months old.

 

[Old Man with Gun]

This may be a mystery that never gets a clear answer. If you find anything on the bolt or case head, I'm curious.

 

[supercorndogs]

This is more like a fantasy guessing game, in which none of us have hands or eyes on any of the pertinent evidence and we are playing a million guesses.

While we are at, does anybody remember where I left my needle files? I can't seem to find them, and I need to sharpen my pruners. Or do you guys think they are sharp enough?

 

[Rec1er]

This is more like a fantasy guessing game, in which none of us have hands or eyes on any of the pertinent evidence and we are playing a million guesses.

While we are at, does any remember where I left my needle files? I can't seem to find them, and I need to sharpen my pruners. Or do you guys think they are sharp enough?

I`d sharpen them ,

 

[Zeroit]

Every ar I've ever seen when loaded leaves a dent in the primer . I don't believe that happens until the bolt stops in battery. A slamfire should Just come out the business end not cause failure like that. I think you and some others are correct something else was going on especially the firing pin
possibilities. I guess we will never know. Not enough evidence to prove definitively.

 

[supercorndogs]

I`d sharpen them ,

Well that would be nice of you. Where you at? I will send them to you.