AR slamfire and or OOB incident

SO, Was at the range yesterday with my son shooting my Retro AR build

This is an M16 Parts kit less Barrel and Receiver.



Incident:

Shooting offhand at 100 yards, sometime around round 5/10 I had a double fire. Pulled trigger once and 2 rounds went off one after the other. Stopped and saw a stove pipe. Cleared the stove pipe, nex round was not fed and the bolt put a dent in the middle of the case. Pulled upper off of the lower and immediately thought the dis-connector was faulty. I"ve had that happen before on a Delton Stock trigger which is what is in it. But I had swapped out the out of spec part and previously had about 400 rounds on this trigger group. It held after every pull back of the hammer and clicked and held when releasing trigger. I then ran 1 round in the mag at a time holding trigger then letting go listening for the click. Did 3 rounds, then stopped after looking down and seeing the round that stove piped. I thought I saved the round but looked all over this morning and could not find it so I drew what I vividly recall after inspecting it. It appears that it was Out of Battery but I feel that it did not initially ignite OOB. Its as if it ignited then the bolt let loose before the gas pushed it back. The reason I think that is a) Case did not rupture b) primer is slighty bulged out and the back end of the case is bulged so it was not fully locked before the pressure in the case came down c) I don't see any obvious damage to the gun and don't recall any puff or pressure releasing out the receiver (although some may have). I have YET to fully pull the AR apart and look at the bolt but figured I'd post this so I know some things to look at and people can monday morning quarterback this. I know already that a PROPERLY FUNCTIONING IN SPEC AR should NOT slam fire unless the bolt is closed. But this is an original Colt M16 parts kit so my thought are I need to step back an inspect what put together in this kit before going any further.

These are reloads I built about 3+ years ago.

Additional thoughts are did I have a high primer? I know there are arguments that a high primer can set off as well as arguments through tests that it can't.

Some thoughts I had before ripping it apart after sending post is:

high primer?

deformed primer?

sensitive primer (yes, I know, all rounds get an initial dent on the primer from closing the bolt on an AR)

Out of spec bolt parts (lugs, pin, pin slot allowing wiggle?)

out of spec Barrel (barrel is new)

combinations of above.

Things I plan to look at:
Bolt face
Bolt Lugs
Bolt Pin
Firing Pin
Lube I had on it
re inspect my 223 reloads (undisclosed amount) and mark the ones I have re inspected.

The bulge and shoulder in your drawing tells me it fired OOB.
Disclaimer- I am nowhere near as knowledgeable as Clandestine, et al.

First thing I’d check is the orientation of your fire control group springs and make sure they are correct.

I’d also check to see that the firing pin moves freely inside the bolt and isn’t somehow stuck in position.

This happened to me because my trigger/hammer pins were walking. The spring legs were not correctly resting on those little grooves. So I 2nd inspecting the FCG.

I fixed it an now my dogs are safe from the ATF.

First of all, if the bolt was not locked, the firing pin won't reach the primer. My GUESS would be that it unlocked early.

What kind of ammo?

Head space?

John from MD said:

First of all, if the bolt was not locked, the firing pin won't reach the primer. My GUESS would be that it unlocked early.

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Yes, that was my first thought, just don't know how. The thing is, it also slam fired I believe. However, there is also the possibility my dis-connector test is invalid or I bump fired the 2nd shot.

Doco Overboard said:

What kind of ammo?

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Reloads

outrider58 said:

Head space?

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I have a head space. Will try to get to that this week.

As mentioned, maybe I bump fired it by accident? Maybe there was some bolt bounce on the bump fire that with the timing allowed it to release early? Only slow mo video at the time of the incident could probably rule things out.

I pulled the bolt and looked at the rear lugs of the bolt and the corners are more worn out than my most well used AR.

Melnic said:

Reloads

Click to expand...

I take the additional steps of squaring the primer seat for my semi auto rifles and then make sure primer is seated below flush but not so much as to distort or oversensitive the primer from being too deeply set and crushed. I seat the primers with a hand actuated tool initially but always finish with a die.
Also I make sure when re-sizing that cartridge headspace agrees with chamber headspace always keeping in mind the ability of the action spring/mechanism weight and inertia to have enough strength to effectively resize a cartridge as its being fed into battery.

Dirty mechanisms, shape of the firing pin tip and length of the firing pin with oos or high overly sensitive primers can cause problems if not carefully monitored or adjusted properly.

Luckily to date Ive never had any slam fires or oob issues with anything I rolled but that doesn't mean it cannot happen or the probability is non existent.

Need pics of cases.

atblis said:

Need pics of cases.

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As mentioned in the original post, I can't find the bulged case.

As for the other cases I shot, I'm not sure which ones were mine and which were from my son's AR. Less than 10 came from Mine and more than 60 came from his.

did your son shoot the same reloads?

Back in the day, the MAS semis could be turned into autos just by reloading them. (the French never thought of a rebound spring and the firing pin was massive) Ten rounds of basically .308 ammo in a rifle that weighed about that of an SKS and it tended to move some.

camo556 said:

did your son shoot the same reloads?

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Yes We both did with his AR, A mix of those plus some from another batch with lower quality projectiles.

Melnic said:

Yes We both did with his AR, A mix of those plus some from another batch with lower quality projectiles.

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so.... his rifle did not exhibit problems? then I'd say not the ammo, it's the rifle.

I won’t be so quick to rule out the ammo as a contributing factor just yet as I don’t expect the incident was caused by the loading characteristics but more plausible an error in the loading itself.

Here however are a couple pics of the wear on the bolt locking lugs that MAY have contributed to the incident.





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Full auto without the paperwork? What’s to complain about?

Melnic said:

I won’t be so quick to rule out the ammo as a contributing factor just yet as I don’t expect the incident was caused by the loading characteristics but more plausible an error in the loading itself.

Here however are a couple pics of the wear on the bolt locking lugs that MAY have contributed to the incident.

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Click to expand...

Nothing wrong here. What you are seeing are the relief cuts on the bolt lugs and the tool marks resulting from same(notice the finish is inside the tool marks surfaces). If this were a left hand bolt, the cuts would be on the other side of the lug. They are created to aid in the unlocking of the bolt.

Do you case gauge your reloads? There might have been a problem with that round.

Did the bullet clear the barrel?

If the case did not rupture, there was not a lot of pressure. So either it was an early unlock or if significantly out of battery, then there was not a lot of pressure generated.

Melnic said:

I won’t be so quick to rule out the ammo as a contributing factor just yet as I don’t expect the incident was caused by the loading characteristics but more plausible an error in the loading itself.

Click to expand...

You said there was a double fire. Soft primers will increase the risk of a slam fire, but you still need the firing pin to stick out, either because its dirty or because of hammer follow (hammer follow because something is wrong with the disconnect or FCG), or some issue with the firing pin/BCG itself.