Ar9 out of battery discharge

[212Josh]

Hello all, I have a Ar9 that I have about 5-600 rounds through. It’s worked well after breaking it in some where I was having a failure to eject in the first 100 rounds. Today while shooting I had the only out of battery explosion since owning the firearm. It blew the mag out of the well and had a shredded shell casing in the action. The round cleared the end of the barrel and short of the mag being blown out of the gun I’m not sure if it felt any different. I have a ar9 specific drop in trigger (Edit CMC trigger) as well as ar9 buffer spring and heavy buffer. Any insight of what to look at and check would be appreciated.

 

[PazAttack86]

what kind of ar9 was it? what bcq, barrel etc?

 

[212Josh]

Its a complete brigade upper with their 7.2 oz buffer and spring on an Anderson lower, stern defense mag adapter and cmc ar9 trigger.
I tore it apart today and found the buffer retaining pin was severely bent and think this might be the issue. Although it seems like that would not cause bolt bounce, in my pea brain it seems like the spring and buffer coming out of the buffer tube would cause extra pressure to hold the bolt close.
Maybe my BCG is too short. (Edit, no it’s not)
Thanks for any input.

 

[LongNose]

How high in the upper does the mag present the round? Seems like the bolt slammed the next round hard enough on the primer to ignite

 

[212Josh]

How high in the upper does the mag present the round? Seems like the bolt slammed the next round hard enough on the primer to ignite

It has run 600 rounds with zero feeding issues. The rounds that blew up outside the breach had a normal primer strike and the bullet made it out of the barrel.

 

[LongNose]

Reloads or factory ammo?

 

[LongNose]

Either way it was probably the ammo if you haven't had and feed8ng issues to date

 

[212Josh]

Reloads or factory ammo?

Winchester white box

 

[212Josh]

How high in the upper does the mag present the round? Seems like the bolt slammed the next round hard enough on the primer to ignite

 

[BkBigKid]

Ok the round cleared the barrel and the case was blown apart.

I am thinking the bullet didn't completely go into the chamber. Either to long or had a buldge in the case but it had to be close to closed as it cant fire it the bolt isnt almost closed.