I suspect the bolt being out of battery is what prevented the firing pin from contacting the primer when I pulled the trigger.
I suspect you're right, that's what it is built to do.
The "receiver extension" is usually called the buffer tube.
SO, gun was apart, cleared, and is now cleaned and back together?
Did you, by any chance save the round with no primer?? It would be very useful to have.
My first guess would be that it was not a few grains of loose powder that jammed the rifle. I think the rifle jammed on the case which was also dribbling a bit of powder. I've had jams just as you described with ammo that wasn't leaking powder, so I doubt the powder was the culprit.
Back in the 80s I had a batch of "crap" ammo, loaded with factory second soft points, mostly, intended just for blasting. The stuff was cranked out on a Dillon 450 without much care for brass prep or the usual QC.
The AR I had at the time, would jam solid on some of them. Bolt just short of proper lock up, and no amount of force on the forward assist would close it, and there was no way a human could use the charging handle and open it.
(personal note, I will not "mortar" an AR unless there's no other choice because someone is shooting at me)
The bolt carrier was stuck too far to the rear to allow the gun to hinge open but I was always able to get the upper off by popping both front and rear pins. With the upper off, a slight tap rearwards on the front face of the rear of the carrier would pop it free. After the second time it happened I did the same thing. After that, I didn't touch the forward assist again.
it happened several more times (I had several hundred rounds of the stuff), and if I didn't hit the FA trying to close it, the rifle only had to be taken apart about half the time to clear it.
I wound up putting that ammo through my Mini 14. I put the rounds that jammed in the AR through the Mini 14. Most ran without issue but a few did stop the Mini's bolt just short of fully shut. A wack on the back of the op rod handle ALWAYS locked it shut, and the round would fire.
SO, if you still got that primerless round available, measure it, and see if it is different than what it ought to be. Especially shoulder and neck, as a first step. I think its possible that if a primer didn't get put in, the case might not have been properly sized, and I think that is more likely than a little powder causing the jam.
I could be wrong, I often am, If you've got the round, (and you're a glutton for punishment,
) shake the powder out or plug the flash hole and then try and rechamber it. If it jams, it was the round, if it doesn't it was the powder. Probably....
