Had a guy come into the shop where I work part time.

Has a Oly lower with what appears to be a CMP bbl on it. the Bbl is stamped CMP on the underside before the muzzle.

The extractor and ejector springs are good and tight. No obstructions in the gas tube.

The rifle will not extract/eject reliably.

He said it is a hit and miss thing too, sometimes it will fork, then it wont.

Is there a diffrnece between the A1 and A2 FSBs?

It seems the only possible problem in in the FSB.

Any Ideas on what to check?

Well, all the rest of the gas system is fine, the ex/ej springs are fine.

There are two worn spots at the FSB as if somone replaced it. The only thing I could think of was that the FSB was not lined up correctly on the gas port. Thus my question about A1 vs. A2.

I dont know what the problem is, everything seems like it should work.

Are you having short stroke problems?  Will the bolt lock open after the last round in mag is fired?

Unknown if that is happening.

If it was, what should I check?

I read the FAQs, but all the links to the troubleshooting guide were dead. The FAQ said that the gas tube and rings might wear out, and that the gas key might be loose, causing short stroking.

How can I tell if the tube/rings are worn?  What indecatiors will there be? The tube does not look "spread out". and the rings still look new, no rounding on edges, still semi-tight in the Carrier.

Most of the CMP type barrels do not use the standard taper pin set up.  Instead, the FSB is attached to the barrel using setscrews to allow the FSB to be indexed/adjusted to center out the rear sight at initial zeroing.

Now on this type of barrel set up, it is important to make sure that the barrel port is set dead center up when installing the barrel without the FSB, to allow the FSB to indexed and not block the alignment of the ports when its added after barrel install.

Now to hit the key points for trouble shooting on this rig,

Start off by checking the headspace.  You may find that it is chambered in 223, which means 5.56 ammo will not function in this rifle.  Also, check the sidewall space to confirm that the chamber has not been reamed so tight that it will not function (read too tight/bolt action match chamber, or tooling marks). If you have a Wolf round, drop it into the chamber with the upper off the lower. Tap the muzzle on the carper to seat the round, and then point the muzzle straight up.  The lacquer cased round should drop out of the chamber.  If it sticks, the chamber sidewalls are too tight/rough for an auto-loading rifle.

The next is if the FSB is installed with setscrews, pull it and check the index of the barrel port.  If it’s not TDC, then the barrel will need to be re-installed correctly.

If the FSB has been installed with taper pins, then you will need to pull it and check the alignment of the FSB and the barrel port.  The FSB holes may have been drilled, FSB installed with the ports not aligned (forward or rearward, or canted).

To sum it up, you will need to pull the barrel apart and confirm that it was built/re-built correctly with everything aligned and spaced correctly.

Quoted: Is this a Centurion lower? Century Arms made by OAI?

I do not think so.

I will try the suggested, thanks

BTW, the ammo used up to this point has been PMC .223 ammo, not 5.56mm. The owner got a couple of boxes of XM193 that he is going to try.  

Thanks for the help. If it had been an extractor or ejector problem, I might have figgured it out, but the nuances of the gas system are somthing that I am still learning.

HS GO gauge is good, not tight, not loose, bolt closes.

will check back in after I meet the owner.

Shortstroking seems the mostlikley right now, the gun will extract and eject fine by hand. Will Check the suggested things. thanks.