This is an instructive post, this recently happened to my rifle.  The take home lesson is "watch your ammo" and for people to see what exactly happens when an AR blows the fuck up.

My buddy was shooting my rifle, using a magazine that had been in his ammo box for a while.  He does reload but both of us shoot allot and a random round might have ended up in it, even in the dark.

I have two guesses as to what happened, but I'll let y'all say what you think happened so as to not sully your thoughts.  

No one was hurt, but it was exciting.

I've already replaced the rifle.

That is a piece of the BCG between the upper and lower

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This was recovered from the barrel... total weight was 83g

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Sorry about your gun OP.

I'm guessing squib load. Bolt was then manually cycled followed by a normal load.

I'm guessing loaded 300 blackout into a 5.56 barrel.

83gr's too light for a .300 in a .223, too heavy for a single .223 .
certainly appears to be 2 projectiles, but without more info (click, manual cycle, fire?) can't know.

My guess, too

Did your buddy pay for the new rifle?

Out of battery discharge of a larger caliber?

Looks like a oversize bullet to me, necked down and squeezed out in the barrel. I'm going with 85gr 6.8 round in a 5.56 rifle.

y'all have found my two guesses.

I'm thinking 300, because I can imagine the bullet losing weight easier than having two rounds fuse so completely.  It can't be seen but the copper on the recovered projectile looks like a hollow or soft point.  Which would mean that the first round (or only round if it was a 300) found its way in to his magazine.  So whatever it was he didn't load it.  Yes it was click-manual cycle-kaboom, which is why my buddy thinks two rounds with the first being a squib.

Yes, he felt worse about it than me.

I'm amazed you don't see more user injury from this stuff

I am very impressed with the ability of the gun to NOT injure someone after this.  I think it would have fucked up his hand (not severely) if he had used a magwell grip.  And that's ironic, because I have laughed at that particular argument against the magwell grip.

that's how you know he's your friend

Is the lower damaged?

Yes, the magwell is about a 1/4 inch wider than it should be now.

Do either one of you guys own or ever owned 300 BO? If yes, that is the answer.

Neck separation of the previous round, and following round kaboomed and extruded through/beside it?

let's think this through.
if the misfire was a .223 squib you would have manually ejected a empty .223 case and it would have been mixed in with the others, no clue there.
if the misfire was a not in battery .300 followed by a in battery .300 (kaboom) a unfired .300 would have been ejected, did you find a unfired .300?
can (did) you determine which case was manually ejected?
was it a unfired round? either .223 or .300?
was it (the misfire) the first attempt  after a magazine change, or a number of rounds in?
is it possible the "misfire" was a unloaded chamber due to the bolt carrier not picking up the first round? 
did you recover enough case to I.D. it?

Class Act

Can't tell from these pictures, but it looks like the cam-pin is vertical in the photo.  Odd.  If the bullet were lodged in the barrel, that means no gas to run the BCG.  Weird that the cam-pin is rotated to the unlock position.

did you see the case when he extracted it???

I bet a not fully seated 223 bullet stuck on the lands followed by another shot
1st click was because bolt was not fully seated,
extract the case without the bullet,
manual cycle jammed the stuck bullet in there farther, cramming the second bullet down the case

boom when too much bullet for the barrel.


a 300/223 combo can do the same but the way the bullets look combined with the fact you have to smash the 300 bullet in there with a lot of cycles as well as f/a action I dont think it was a 300.

double 556 bullets can stack with one cycle as I've done it before-narrowly missing a kaboom when i saw the powder next to the gun

Awesome indeed, and why I support the company whenever possible.  Both pieces suffered no damage at all.

But the G trigger is already in another build, and the ALG rail will be sometime soon.

We did not find any unusual brass on the ground.  We looked pretty carefully but it's a busy range, so missing it would be likely.

SO I'm the guilty party here.    IMO the root of this is shooter carelessness on my part.  I was checking out the reticle on this new optic on Curahee's rifle, and grabbed a 20 round magazine out of my box that was all random range pickups. (no 300s, no reloads, etc)  I usually pick them up after matches, and whatnot when I am policing up the area.    SO..  its really that simple... don't shoot ammo that you don't know.     I should have been disassembling them, and harvesting the brass, and possibly projectiles.  

I had a FTF.    Not a squib that I or anyone else could tell.   There was no audible pop, there was no recoil. Just click, and no bang.   I racked that round out.   I SUSPECT that the projectile stayed in the chamber.  Maybe it was loaded long?  Maybe the powder was wet, and it had enough pressure to be lodged in the lands and grooves?  Then I loaded another round in, took aim, and it made a loud bang...  resulting in what you see here.  I suspect that the new round was seated in the chamber, and compressing the 2 projectiles on top of each other. Making a compressed load, etc.  

I have never had a 300aac round in my possession, much less loaded into a magazine.    

This ruined a bunch of good parts, including a lower, and I still feel pretty bad about that. All of it was replaceable, and no one got injured. Thankfully it was not a SBR, or Transferable MG...  I couldn't imagine what I would be doing about that.  I am VERY thankful for no injuries to myself or others, and that it was only a (relatively) cheap mistake.  

My advice...
#1 don't shoot rounds you don't know!
#2 Wear glasses!   You only have 1 set of eyes.  
#3 Don't think it can't happen to you
#3 Use QUALITY parts.. I really think the bolt in this gun saved me.  It is from a majorly well respected maker of Bolts, and it took one HELL of a beating. If this had been some cheapo non inspected bolt, I think the gun may have actually come apart, and injured me.  The bolt REALLY saved the day.

if you didnt have any 300 BO then its basically the only way.


did you see any unburnt powder anywhere

Thank you for posting.  

I've shot and seen people shoot a lot of ammo of unknown progeny.  Everything from seized ammo that is ordered to be disposed, to store return ammo called in, to widow's clearing out cabinets, to you name it, to someone doing range pickups.  I've seen someone purposely collect up range pick-ups over weeks, and then spend an entire shooting session just shooting that ammo (which boggles my mind that he was able to find that much).  In that time, I've learned about range pick-ups two things:
1) Beware 9mm ammo, as someone may have been trying to "make major", which is IDPA shooters super-charging 9mm in a purpose reinforced 9mm, to basically .38 super power; in a 9mm.  
2) Beware of wet powder.  A decent portion of range-pickup ammo has wet powder/wet primers.  


Neither of these in themselves will typically cause a kaboom in a good strong arm, but they can sure cascade into one - particularly the wet powder.  Because of exactly what happened to you.  Either that, or you had a 6.8 that looked like .223 and missed it.  But more likely, in your case, that first shot had wet powder and squibed, and the next shot went right into it.   The biggest question though is what happened to the wet gun-powder, from the squib?  I would expect there to be unburned powder either in one of the cases on the ground you inspected, and/or in the gun - and it doesn't sound like either was found.

[Edit to add - this is NOT an endorsement.  Even though I've seen lots of shots fired with that sort of stuff, this is never going to be something that's going to be labelled as a "good idea"!]

We did not see any unburned powder on the ground mainly because this shooting area was wet clay with TONS of other casings, and debris all over the ground.    None in the gun either, but after that much gas going everywhere, I doubt there would be.

Don't shoot range pickups period.

I have seen some outrageously bad reloads at matches.  Super hot rounds that split brass and blew primers, powder puffs that squibbed, uncrimped/undersized rounds that literally fell apart in the magazine.

No way I would shoot anything picked up from the range.  I also won't reload rifle brass from the range (unless it's mine) and I inspect range pistol brass VERY carefully.

yep

nope

Please read thread in entitety

Every time

just going out on a limb here but they "may" want the rail and the trigger back to inspect them to see how well they did hold up during the kaboom. thats some serious R&D that companies can't get any other way unless there is an accident. by returning them to "G" it can help make the product even better. JMHO