I have a pre-ban Olypic with a 16" barrel, I shot it the other day and the first 30 rounds went off like a charm; but then the problem started,it would shoot one round and jam then again and again. I went back to the original mag. and had the same jamming problem. I had different ammo in the clips, so Friday I am going to try it again with all the same ammo, but I was wondering if I have the same problem if I could change out just the bolt assembly not the whole carry,or would this still require a head space check. I have another AR I could borrow this from. Thanks Autogunner.

At this point there is no need to get a new bolt as the problem is probably the extractor.  When was the last time you removed the extractor from the bolt and cleaned it?  If you have cleaned the extractor and still have the problem then it is probably either the extractor spring and or insert.  Get a new, extra power extractor spring from Wolff Gunsprings and try it.  More than likely this will fix it. This is a fairly common problem with AR's. If the gun has had a lot of rounds through it the extractor claw could also be worn.  Personally, I would get a new extractor, spring and insert, all quite inexpensive.

The only other thing I can think of and this rarely happens, usually with a new barrel is that the chamber is too tight and needs polishing or you are not cleaning the chamber properly.

Lastly, if you are shooting highly lacquered ammo, such as Wolf or some of the South American stuff the chamber, when hot will become "sticky" with lacquer and cause FTE's.

Just saw Dano's post after mine.  Listen to him, he knows what he is talking about!

Jamming describes a lot of problems,

Please be more specific in how it was jamming.

I assume you mean jam as in not ejecting/extracting...or not feeding right?

If it's not extracting, as mentioned, it could be the extractor claw or spring.  I had a problem with failure to extract.  But the problem was solved when I cleaned the chamber, gas tube, barrel and bolt really well.  I was using Wolf ammo (and this was a used upper, so who knows what the last owner did).  Now it works fine.

Thanks guys for all of your help. Autogunner.