Help troubleshooting causes of a malfunction

[CopperFouling]

That sounds identical to the problem I had with the Ruger.
Part #14 in the pic below is the fire pin retainer. On the Ruger, this can be installed improperly and cause the bolt to stiffen or lock up intermittently

How could it be installed incorrectly? Mine is pushed fully into the bolt carrier. It is oriented vertically.

 

[CopperFouling]

When was the last time you removed the carbon build up in the BCG. This along can cause malfunctions that you described. A neighbor bought a AR very very cheap because it was doing the same thing. The gas chamber was totally carboned up. I have the Otis tools for removing this. It took hours to break all of the carbon out. Once cleaned, rings oiled all was good.

I can check that, but the rifle probably has less than 60 rounds through it total.

 

[Hugger-4641]

I'll break one of my Ar's down tomorrow and see if I can get a better picture.

 

[CopperFouling]

Some rounds chamber and fire fine and others don’t?
If you load a full mag and manually cycle the action by pulling the charging handle and letting it go, 30 times, how many malfunctions do you get?

Correct. I shot maybe ten rounds on Friday, all of them the American Eagle 55-grain 5.56. I had four—maybe—cycle fine. The rest jammed after a single shot.

I can try that tomorrow.

 

[CopperFouling]

The plot thickens.

Some rounds chamber and fire fine and others don’t?
If you load a full mag and manually cycle the action by pulling the charging handle and letting it go, 30 times, how many malfunctions do you get?

I used the same American Eagle 5.56 55-grain rounds that were jamming at the range. I swapped magazines from the two Gen. 2 Pmags that I was using and used a Gen. 3 Pmag. Starting with the BCG locked rearward, I cycled all 30 rounds without a problem. I was not expecting that, to say the least.

So it could be possible that

• I had two bad Gen. 2 Pmags (one a 10 rounder and the other a 30 rounder) that have been responsible for the jamming
  
• something is interfering with the BCG reciprocating all the way to the rear, which in turn is preventing it from going all the way forward into battery, or
  
• something else I have not considered.

The first seems like the most likely from a mechanical point of view, but what are the odds that I had two bad Pmags in a row?

I can try hand cycling the rounds using the other two magazines tomorrow.

 

[Show Me]

The occasional over enthusiastically crimped round will enbarrass you every time.

 

[mjsdwash]

Get Okay magazine. As in Okay industries. 26,500 rounds on them with 0 malfunction on my side. PMags/everything else not so much.
Second, run some standard ammo again. If it works, its probably bad ammo.
If its not the ammo, contact the manufacturer. A $700 rifle with a $1300 name premium (not trying to offend, but its what it is) can pay for some extensive customer service.

Edit to add. Not everyone has had good experiences with PMags. In fact, some of us swore them off. I am one. So was the US military until some political complaining. While I have never had a malfunction with their 30 round mags, I can tap the bottom and have rounds fall out the top. Can't do that with ASC, Okay, NHTMG (Okay industry, may be spelling wrong), Brownells, C-product. Also, the 20 round Pmag cause MANY problems.
PMags do not allow extremely long OAL (my experience only), so a 77grain may be failing to allow the spring to keep up. Too long, and the bullet drags. This means bad feed angle when the bolt comes back.
Try ANY aluminum mag and see if the problem goes away. Plastic takes more space than metal for a given strength, and no one will dispute that. PMags are stronger than aluminum mags. So logically PMags must be MUCH more voluminous than aluminum mags. Heavier bullets are more likely to push the OAL lime, and plastic mags are more likely to encroach on that length. Add curvature and things get problematic.

 

[243winxb]

So it could be possible that

• I had two bad Gen. 2 Pmags (one a 10 rounder and the other a 30 rounder) that have been responsible for the jamming
  
• something is interfering with the BCG reciprocating all the way to the rear, which in turn is preventing it from going all the way forward into battery,

The mag lips may be making contact with the bolt? Should be able to watch with empty magazines.

In 1979, when i got my brand new COLT M16A1 , it was a jam-a-matic with the 20 round factory mags that came with it. Lip drag problem.

 

[1KPerDay]

Hand cycling won’t tell you much. Make sure you’re letting the bolt fly home with the full force of the recoil spring. And make sure you’re pointing the rifle at a brick or concrete wall if you’re hand cycling live ammo at home.