This is kind of long but here are the facts.

I already posted a story last week about my new upper test report. In that post I mentioned that I found some split cases and all of the fired brass was smoked up or burnt looking.
This ammo was brand new UMC 115 gr. FMJ.

After that range trip I inspected and cleaned up the chamber area, forcing cone in front of chamber and the cone area of the bolt. All these surfaces had a real heavy and gritty phosphate coating and I was concerned that it was holding the bolt back from closing completely.

I polished these surfaces by using some fine
or mild 3M Scotch-Brite wrapped around a cleaning jag and chucked in a drill to spin it.
This polished it real nice and smooth with no metal removal at all.

Also checked headspace best I could by taking a loaded round and measuring it to verify length and painted it with a black Sharpie.
Chambered with bolt (firing pin removed) and then checked that case mouth was making contact with front of chamber evenly and that bolt was not holding off seating. All looked OK.

Back out for a shoot and still had a couple split cases! Tried a differant brand of ammo, Olympic 124 gr. FMJ, for comparison.
After 20- 30 rounds I checked spent brass and found some with blown out primers! Shot couple more and POW!! had a round blow the base off and stuck the shell casing in chamber!! Funny thing was that I was holding it at waist level and watching bolt on these rounds to see if it was closing completely and it looked like it was. Talk about a scary face full of fire and metal bits! Good thing I wear glasses or I could have lost a eye!

That Olympic Greek ammo must have a thinner case or differant dimension than UMC.

OK, now its back to the house because the stuck shell casing is not coming out easily. Futher inspection shows I also now have broken firing pin! And face of bolt has primer pocket imprint!
I don't think I will be shooting this baby again until it goes back to OLYMPIC ARMS.

On a bottleneck rifle case I would say I had a oversized headspace problem from the evidence so far?

Any ideas ????????????????????

My guess is that the hammer is following the round and detonating it before it seals into the chamber.

Or...the chamber is too large and is allowing hte case to swell and explode.

TRG

Send it back for another upper.. I'm sure they will make things right.. Sorry to hear about your problem. I know I wouldn't trade my 9mm upper for the world!

Yeah, send it back into Oly.

To provide some more info:

Buffer and spring are standard CAR-15 stock set I have been using on 5.56 upper with no problems
A heavier spring or buffer may be a good idea to try and delay blowback movement. Would a standard rifle size spring or buffer be any stiffer/heavier? And will they fit in four position CAR stock?

Hammer and trigger group are same unit used with the above parts from my 5.56 CAR-15.

Semi-auto only

No suppressor

Pre-ban flashhider on 16" barrel

Ammo has all been factory loaded FMJ, 115 gr. and 124 gr.

Same results using the Oly supplied modified Sten mag and SOCOM block with Sten mags.

No changes made to lighten bolt/carrier assy or hammer spring, etc.

Closer inspection of cone area in front of chamber shows an irregular machined step kind of like a burr or non-clean up at radius area where cone turns into chamber. Looks like it could be holding bolt back from full closure.

My cleanup and polishing efforts didn't open the chamber up any as I stayed out in the cone area only where it had heavy, gritty phosphate coating.

I have not measured the chamber diameter yet but that is a good question.

I will be on the phone to Olympic Arms Monday morning for certain. I'll let you folks know what happens.

I really enjoy firing this unit, I hope I get its problems solved.

Time for a new bbl from Oly at their expense.

To my knowledge a standard buffer in a car buffer tube wouldn't work and is probably a dangerous thing.  If you want, there are heavier CAR buffers out there.  The "H" buffer is a little heavier than a standard CAR buffer and there are 9mm CAR buffers that are heavier yet.  I just got a 9mm CAR buffer from "shurluk" at the PGCA gun show this past weekend.  Haven't tried it out yet.  Best to send it back if your not sure as to the problem.

I have an Olympic 9mm carbine,can I put on a pinned collapsable stock(legally).And do I need to use the olymp spring and buffer or use the collaps stock spring and buffer which was used on a 223.thnxs

I would check the weight of the buffers and use the heaviest one. And like I found out the full size rifle buffer will not fit in CAR stock. Lay them side beside and you'll see a big length difference. Same for springs.

A fellow over on the Troubleshooting board here on AR15 gave me some good info about how the 9mm works straight blowback and the weight of the buffer and spring are all that keeps it closed and regulated for opening speed/cycle time.

I heard back from Olympic Arms Friday that they were sending me back my unit after review.

They found a short carrier the e-mail said.
I don't know what effect that had on the performance but it must not have been a good thing based on my experiences.

Also I weighed my buffer that came with CAR stock and it was very light versus the recommended weights mentioned on Bighammer website. I have increased its weight more up to levels listed for 9mm carbines. And ordered a Wolff EX Car Spring to beef up the recoil system.

Hope to give this bad boy a test drive next week with all the improvements included. I'll let anyone interested know results.

Maybe also time to spend a little more.  If you are on a budget, MFS Hungrain made ammo has some excellent thick cases and it's hot to boot!

Otherwise, time to reload.

I own a Olympic arms 9mm, but I'm wonder what they said by "They found a short carrier the e-mail said." in the email they sent you.

Doesn't make sense to me.

Took the 9mm upper out for a test run of 100 rounds of UMC ammo after the folks at Olympic sent it back to me.

All went very well without a single problem now!

The Warrenty and Repair people I talked with and the quick turn around was a good experience.

Like I said earlier the short note I received from Olympic only said they found a "short carrier". Now with the new one in it I can see a difference in the way it closes up tight.
Before there did not seem to be much spring pressure holding it shut for first little bit
of movement. Now with the new carrier it is pressed up against chamber very tight when closed.  

Ahhhh, the wonderful sound of customer service....  Been nice if it had been right from the get-go, but since they took care of it...  Looks like I'll stick with my decision to get an upper from stokes as soon as my wife lets me have some money.