This happened awhile ago, but it finally dawned on me to ask here.

I've heard a popped primer is a very bad sign. I was shooting my Yugo 59/66 SKS. I normally shoot brass case ammo and have never had any issue. I was trying Wolf ammo for the first time and while shooting had a primer pop out of the case.

Is this an issue with my chamber or could it be an issue with the ammo?

Clean the chamber. Fouled chamber can stop the case from expanding fully, therefore increasing pressure and popping the primer. The wolf ammo is also very likely to have less tolerance on the O.D. of the case and would cause higher pressure. I had the same thing happen in one of my larue rifles, started popping primers with factory match ammo. Cleaned the chamber well, and been fine ever since. I now clean the chamber much more often.

Or it could have just been that one round.

I had always read the stories of bad factory ammo with a grain of salt, thinking it was internet stories.....until one day....

STORY TIME......

A buddy and me are out in my back "yard" shooting, he is shooting I am shooting, both just dinging steel about 10' away from each other....he is shooting a factory box of 40 in some plastic fantastic....does not matter the hand gun in this story.  I am shooting a revolver six bangs and done to his sixteen bangs and done.

I am reloading and watching him as I do, and his slide does not go back into battery....hmm, it is out by a good way.  I see him bang the back of the slide, no go, so I see him rack another round, and the same result.  He drops the mag and the thing will not go into battery.
There is a live round that has tried to be pushed home that it takes a knife to get out, did not think he hit it that hard.  And upon looking there is a bullet stuck just inside the barrel....oh boy this could have been bad for all of us all the way around.  

Back to the house and with a cleaning rod I poke out the bullet....and then dig out a case still stuck....I am trying to figure out just how in the hell this all happened....it just does not add up.  He says that before the squib everything was fine, the squib sounded fine, and the gun cycled.  I was standing there looking but not really watching....you know how that is.  How could it have cycled with a round that left a bullet with rifle markings on only half of it...it did not travel that far.  Why did that case not eject if the gun did cycle....the gun had to have cycled as I do remember the shot not sounding different and the slide not closing the first time.  All very very strange.

We both decide that we need to watch for impacts a little better when goofing around and mark it up to a bad round in the box....that case looked no different then any other fired case.

That was my first and only first hand experience with a bad....I guess bad factory round, I did have a box that had one round with no bullet and powder all over the place, but it never got as far as into the gun.  

I still really don't know really what happened or how it happened, it just still does not add up.

Anyhoo......

If you made it this far, I would say if it does not happen again think bad factory round, it can happen.

Popped primers can be a bad sign, particularly in association with other excessive pressure indicators or headspace issues. I had a CZ52 that regularly popped primers until one day I experienced a minor Kaboom that resulted in the base plate of the mag being blown out and dumping the spring, follower and remaining cartridges onto the deck.

HOWEVER, an occasional popped primer can just happen without it indicating any further need for concern. If it starts to be a regular occurrence or if you are seeing bulged cartridge cases, hard extractions, splits in the cases, etc. then I would stop shooting and diagnose the problem.

Does the bolt match the receiver?  Headspace may be off.  Some of the SKSs where ones that were through together from various parts. Look at M1 Garands. It is common to see them as mix masters.

My Garand has a Winchester trigger group. H&R op rod and Winchester bolt. All on a Springfield receiver.  The importer may have picked up  a lot of riles that were from a rebuild armory and it could have just been a pile of parts