Had a bit of a problem at Gunstock.  Bear with me, this might get long.  

Rifle was (originally) a pre-ban Oly with a completely unmarked upper.  Literally, no marks anywhere to identify a manufacturer or chamber type, so I'm assuming it's a .223 chamber. 16" bbl.  I purchased a case of South African "surplus" .223 from Cole Distributing.  It comes in the brown tapered cardboard box holding 30 rounds.  Not sealed.  Only distinguising marks on the box are "Lot 5".  From what I can tell, it's what Troy has described as the newer production S.A., post-battlepack, that is loaded to SAAMI spec, boxer primed.  Basically, commercial ammo in military-type packaging.  

I break open the case at Gunstock and load up a 20-rounder, which fires without a problem.  On the next round, I get a "bang", but the rifle does not fully cycle.  The bolt is being held open by a live round which is wedged against a spent case stuck in the chamber.  I tapped it out with a cleaning rod and see that the extractor has shaved off brass from the rim.  Since I think it's a .223 chamber, my thought is that the case is stuck because the chamber is too tight, or dirty, and the extractor ripped the rim while trying to pull it out.  

Since I was planning on buying a new upper anyway, I went to the vendor's tent and bought a DPMS upper (M4 profile barrel, CAR handguards, flattop - very nice).  The barrel is clearly marked "5.56", and the DPMS guy confirms that it's a 5.56 chamber.  I slap in on the rifle and for good measure change the extractor.  Back to the range.  

Ran one mag through no problem, then the exact same thing happens.  Cleared it, tried again.  Bang, click.  Now I'm pissed.  Same problem, two different uppers, one probably .223, one 5.56.  The consensus among the folks who were witnessing my problems was that the brass was soft.  I probably went through this close to 10 times, and every case had the brass shaved off the rim by the extractor.  

I ran a box of Winchester Q3131a through my rifle with no problem, and later ran several boxes of Sellier & Belloit without a hitch.  A brave soul let me shoot my ammo through his AR, and after several rounds, the same thing happened - stuck case, shaved rim.

Has this been reported or observed to be a problem with this ammo in the past?  Am I correct in my thinking that this appears to be an ammo problem as opposed to a rifle issue?  

BTW - Cole no longer lists it on their website.

Thanks for any and all insight.

Just as an insurance measure, I would get a stronger extractor spring.

The ammo is loaded light. I have a case I bought when Bob Lippman was humping for Coles. They assured me via email it was true M193 spec. It isn't. Never locks the bolt back and occasionally short strokes. That applies to three ARs. Works fine in the Mini so it is reserved for that rifle.

When I replaced the extractor, I also replaced the spring and the little polymer insert.  The new spring is a lot stronger than the old one; I had a tough time getting the extractor pin back in.  Still had the same problems.

I agree.  I have a battlepack's worth.  It will not lock the bolt back and short strokes often on my 16" EA but works fine in my 20" Colt.  I have stayed away from this ammo since buying the one pack.  
   

Hmmm,  Mine did the same thing to a LC round on sunday at my local range. Part of Lip shaved right off.

Except in my case the bolt was stuck forward, Had to smack the but hard on the ground to seat it and pull the bolt back.

The brass was "shaved" off what would be the inside edge of the rim, where the extractor would hook on.  The extractor did not tear through the rim.  

I did notice some soot around the neck of the fired case.  There was nothing unusual about the recoil, but if I had to compare I'd say it was a little lighter than the Q3131A.

Unfortunately, that's about all I can tell you.  I'm planning on a range trip in a couple weeks, and I'll take a couple boxes with me to see if I can duplicate the problem and make better observations.  

Troy or anyone else who is "in the know", I would like to draw on your experience to figure out what's normal.  Should extractors just leave a surface mark on the case rim?  Or is it normal for them to actually deform the rim slightly?  I'm talking about Miltary pressures here, not SAMMI;  XM193, Q3131A.  Thank you.