Hmmm?  Is there a physical limitation with the solid 9mm bolt assembly that makes it not possible, or is the industry just happy living in the 70's?

I'd say its more a minimization of failure points. A fixed ejector is much older than 1970s, AKs have them, 1911s, K98 is fixed for practical purposes. Its reliable. Plunger ejectors can get clogged with shit, blowback is pretty shitty, cleanlinessly speaking.

Would a standard type ejector in a blowback system likely suffer from the same spring tension issues that the rdb system does?

I agree with both posts above.  Fixed ejector is the way to go.  

I understand for the simplicity, and the ease of incorporating the ejector in a mag block, but with the new inserts for p-mags that don't require a mag block it would be nice to have the ejector in the bolt like the CMMG system.  The only real complaint with mag inserts and blowback is the ejector being a part of the magazine, and the manual of arms that it alters.  

I think the major issue in an AR15 based platform would be the much shorter case length in 9mm causing the case to cam outward much earlier and induce a failure to eject and malfunction.

With a longer case like 5.56, the bolt is much further back when the case mouth finally clears the chamber and can sufficiently "fling" out of the port, and the extractor claw maintains control of the case because it's length meas it's not tilted at too steep of an angle as the mouth drags against the chamber and then the inner wall of the upper in front of the port.  

With the shorter 9mm case, when the case mouth leaves the barrel chamber area, it would then shift over to the upper wall, but at that point the extractor claw would probably lose control of the case because it's so short and it would simply fall into the area in front of the bolt instead of eject reliably.

Yeah, I hate the change in manual in arms and think it is an AD waiting to happen if someone not familiar with the configuration uses it.
I am not familiar with it but doesn't the Aero upper have the ejector in the upper?  Maybe that is an option?  
There is also the old Olympic system that had that funky torsion spring ejector that moves out of the way with each cycle.

For someone that really wants to tinker, maybe replicate the Daewoo 556 ejector that is in the lower or copy something like what I did for my hybrid Dissent.
https://c3junkie.com/?page_id=1733

I'm not super familiar with it, but I believe the Aero has the ejector in the lower as standard but that LRBHO is mounted in the upper and only glock mag compatible

I thought that Wilson Combat's AR-9 bolts do:


From https://www.recoilweb.com/ar9-pistol-caliber-carbine-90357.html:

Interesting...haven't seen that one before and looks like the article came out 8 yrs ago.  Wilson Combat usually makes good stuff so presume it is GTG.  Don't recall seeing any posters on it.

Id be interested in learning more about their ejector springs, if they are proprietary or just one of the ar15 wilson ejector springs which they describe as 80% stronger than standard ar.

I sent an email to Wilson asking about the spring and they replied quickly. They said they do not sell them separately and it is not their ar15 ejector spring.

It doesn't appear that the bolt is available for purchase so it seems a moot point anyway, for me at least.  I have an idea I am going to work on next week during my "vaca"

My 3 CMMG 9mm's destroy ejector springs in just a few hundred rounds.  A fixed ejector is far more reliable and long lived.

Seems an odd part to fail so miserably.  It maybe moves what, an eighth of an inch?  Why would 9mm be any harder on ejector springs than 45acp, or 5.56 for that matter?  My RDB 45 hasn't had any problems.

Yes, I've posted many times that my CMMG RDB in .45 is fine as well as all my friends that also run the CMMG in .45 also in full auto.
However, myself and all my friends have ejector spring failures in 9mm, .40SW and 10mm all of which are higher pressure.
Link to my website again: https://c3junkie.com/?page_id=221
This short video shows the slop before the lugs of the bolt impact the lugs of the extension.  I have dummy round in the chamber in that video.


This video also shows what happens when you have a CMMG barrel with an excessive gap / headspace.  It will extract the round with no extractor installed and no suppressor mounted and it destroys other parts like extractors and cam pins.


Imagine what happens to the ejector spring when a round is fired.  Pretty sure it is going solid height when the round goes off. The bolt immediately starts to rotate in this mechanism vs 5.56 where the bolt is truly locked and doesn't rotate until the pressure has come down.
The MEAN Arms bearing delay uses the same ejector spring and I'm on my 3rd one in less than 2000 rounds.

Fixed ejector for me....just eliminate the point of failure all together for these delayed blowback actions.

Thanks for the detailed 411, amphibian.  I might have to get a 9mm RDB setup to see if there is some kind of fix that hasn't been realized.  

I think blowback still rules the roost in 9mm tho, and there has to be a better mousetrap than what is available.  It wouldn't be difficult for a man'f to add some kind ejector to an upper, or lower for that matter, but more than the average Joe can handle and the market is probably small.  I am working on pistol caliber inserts for metal AR mags, and for them to function the ejector has to be part of the gun.  I have an idea....

Do you realize the Dissent is RDB and uses a fixed ejector and look at my link in my first post?

I did see that, but that is specific to their gun.  I think I could fashion an ejector and bolt it to a standard upper for blowback, but that wouldn't be practical for common use.  RBD is the hotness, but there are a lot more blowback rigs in circulation and that is my concern right now.  My 45 is RDB and runs great, no worries about ejection.  My 9 is blowback and runs great as well, with Endomags, but the ejector/mag issue is mildly bothersome.

It seems that putting a fixed ejector in the upper, either with an AK-style fin like amphibian's solution or a spring ejector like Olympic Arms, requires as much gunsmithing as modifying the bolt carrier for a plunger.

I've been on the wait list for the Wilson carrier from Right to Bear, but it's never been in stock for the past 3-4 years that I've been on the list:
https://www.righttobear.com/wilson-combat-9mm-bolt-assembly-black-nitride-wil-16-0004/

You could try to add an HK-style lever actuated ejector that is tripped on the rearward stroke of the bolt. You would probably need to use the trigger/hammer pins as a pivot point, but I'm sure you could WECSOG something in there.

Aside from attaching it to a mag adapter, the next easiest solution is adding it to the mag itself, which is how MEAN ended up solving this.