FWIW, the Olympic Arms (OA) PCCs had a unique ejector assembly where the ejector included an integral spring. The ejector would be pushed out of the bolt path by the bolt in the two inches of bolt travel from and towards the breech. During that two inches of aft and fore travel, the ejector would press against the bolt and add about three to three and a half ounces of effective fore/aft drag force upon the motion of the bolt.  The downside was that the ejector/spring would eventually break.  One could probably put together a separate lever and spring mechanism (with more parts than the OA assembly) that could fit into the allowable space and perform the same functions.  As no slot in the bolt is needed, such a mechanism would provide maintained bolt integrity.

MHO, YMMV, etc.

The MDP-9 has such a mechanism + delayed roller blowback.  Again reviews have been spotty but I don't think it has ejection issues.

Good to know.  Thanks for the info.

I think I got less than 300 rounds out of the 10mm ejector spring I put in my original Banshee.  I found that Bexar Arms sells one made of Inconel X750 and emailed to ask if they had any experience with them in the Banshee design, but never heard back from them.  They aren't cheap at $7.99 each, but I ordered 4 to try (I have 3 Banshee 9mm uppers).  I will report back once I have run them. I plan to take measurements and keep track of round count.

I tried the Bexar Arms Inconel ejector spring in my 9mm CMMG RDB as well a few years ago and it didn't last as long as the MK10 spring.   I need to update my website with that info.

Thats interesting, theoretically Inconel shouldn't wear out like that.

The metal isn't wearing - it's the spring temper that is failing.

Ok. Are these issues still
Ongoing?  How many rounds before they appear?

For me and the people I personally know, it is about 1K for the 9mm.  
For what I see in the internet, it seems to be all over the place, some say it has been like since day 1 and they are disgusted and some say they have had thousands of rounds with no issues.

Just wanted to post an update to my comments above.  I initially got an Angstadt MDP-9 upper to test with to make it full auto capable and use the buffer tube.  However, during the baseline testing before I made any modifications, one of the rollers broke (again running in the stock form).   It took a long time for them to fix it and was told that the issue was the trunion was misaligned.  I had seen a post on Reddit about someone saying one of the rollers broke as well but thought those issues were resolved by now.  Apparently not.  

On top of that, I had friends talk to them at Shot Show as well as my direct correspondence and they were unwilling to sell me a spare trunion and basically any spare parts and everything in that upper is proprietary.

I knew that modifying the Dissent would be an easier route than the MDP-9 but since I was never impressed with the out of box recoil impulse with the RDB, I thought giving the MDP-9 a try would be better.  However since the MDP-9 route was a failure, I figured the Dissent was my only path forward.

BTW, I stumbled across this Youtube video where this guy mentions the same thing about the Dissent not being tune-able and that his tuned Banshee was the smoothest.


If you look at his old video's and comments, his tuned Banshee is my 'old' CMMG setup that I have documented here: https://c3junkie.com/?page_id=280

Here is a link to my site with what I did to get the Dissent to run full auto, re-use the buffer tube and with my custom 'CE - Carrier Extension' even more tune-able with less reciprocating mass than the stock Dissent or a CMMG Banshee: https://c3junkie.com/?page_id=1733






As mentioned on my site, this setup is 'sustainable' since CMMG will sell you the Dissent BCG now.  Think about the MP5 and it's wear items like the rollers, extractor spring and locking pieces.  With the CMMG RDB, it is just the barrel extension and lugs on the bolt.....I guess you could also say maybe the cam pin since it has to take a lot of stress.

I'm at over 50K with my custom SS 9mm CMMG RDB barrel and it is still fine.  I'm only 2K into the custom Dissent Hybrid setup but since the cam pin has been moved further back as pictured below, I don't anticipate the bolt from cracking like they have in my CMMG Banshee slotted bolts for my custom fixed ejector.


Video of Phase I and II in action.

amphibian, that is amazing work.  Let me see if I can put your Phase 2 in layman's terms:

1) Took a heavy, but off the shelf 9mm upper, and cut the Dissent's rearward cam clearance;

2) Swiped your Dissent ejector or fabricated a copy & bolted it into the new upper;

3) Chopped the Dissent bolt carrier into an AR type stub, and fabricated aluminum & stainless extensions to bring it back to stock AR carrier length, allowing auto sears & binary triggers, as well as tuning w/ buffer weights;

4) Added a sprung reciprocating mass in the carrier extension with a hard stop to prevent overcompression of the spring;

5) Used all your previous tuning tricks of various AR buffer springs, buffer tube lengths, internal spacers, and hydraulic buffers from tuning your previous RDB Guard/Banshee.

Is that a decent summary or did I miss something?

I presume you'll be trying a Dissent .40 S&W bolt if they release one?

Yes
Yes, using an APC Ejector since CMMG wouldn't sell me a spare Dissent fixed ejector.

Yes, more details below for those too lazy to click on the link to my site.


Yep pretty much.
Also wanted to stress that the 9mm Dissent bolt has 55 degree angles while the 9mm Banshee is 50.  I'm presuming since the Dissent has less reciprocating mass.  Doing PhaseII, I am able to get the reciprocating mass even with the buffer to be lighter than a factory Dissent config.  15.1oz (10.4 for the BCG/CE and another 4.7 for the RB5005) vs the 17.2 oz pictured above.  So I am 5.8oz heavier than a full size MP5 BCG but the MP5 shoots too fast.

I also did some experimenting with a Delrin buffer since now that I have a spring loaded CE weight to kill bolt bounce I don't need that in the buffer.  I did that with a Troy PDW compact stock and it just isn't as smooth as using the Kynshot hydraulic.  Again, the more compact you go, the less smooth.  I think this holds true even when comparing a full size MP5 to an MP5K.
You mean running a .40SW Dissent bolt in 9mm like I was doing with my old Banshee build?  Or you mean doing a hybrid Dissent build in .40SW?
I would say yes to the former and would probably do a hybrid .40SW Dissent as well since if I did the former, as it would involve buying a .40SW Dissent BCG anyways so I could easily just retire my .40SW Banshee for a hybrid Dissent.

I can honestly say this is smoother than my MP5 and I can dump rounds in full auto on target with this better than I can my full auto MP5 and I have a nice tune-able cyclic rate from the 500's to 700's.

I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits.

If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance?

Could you mill a complete aluminum unitary bolt carrier, or would the cam pin loads just wreck that?

If you were to slot the right side of the upper & screw in a fixed bolt handle into the front of the carrier, could you come close to a constant recoil system in auto?

I thought about that but I purposely bored out the CE to utilize common AR buffer weights that everyone has access to vs custom weights.
I didn't want to go too thin on the Al CE as I was concerned about strength which is also why I copied the Surefire OBC carrier dimensions at the top to give it more strength.
Yeah...highly doubt that would go well.
You lost me there.  You want to add more mass?

No - I want to remove the greebles on the top of the bolt carrier so the bolt carrier can go farther back into the receiver extension, lowering the impact on the buffer tube buffer cap.  Why the Ultimax light machinegun is so smooth - the bolt carrier never bottoms out, all the energy is absorbed by the recoil spring, slowing the bolt carrier to a stop, then pushing it forward.

Oh, yeah.  Don't know if you've seen that I was able to get 5.56 not bottom out like the Ultimax here: https://c3junkie.com/?page_id=1403

I can remove the rear 'stud' on the back of the carrier now to gain another 1/2" of travel before the cam pin would hit the lower....but that isn't the issue....I can really only do about 1/4" otherwise the hammer will slip in front of the carrier like this:


Also bear in mind that in my old CMMG RDB setup I had my carrier machined to go deeper into the buffer tube and cut the key back to use a single bolt as shown below. That configuration was not reliable so I went back to the RB5007.


Now with the hybrid Dissent I'm finding that I am liking the RB5005 more than the RB5007.  I'm only 2K into the hybrid Dissent and still have a few more permutations I want to try and then may try to see what happens if I gain a 1/4" in travel with the Geissele SSF and I can get more with a Milspec hammer.

Amphibian, since you practically home brewed this whole thing, I wonder if you could use a jakyl bolt with custom lug angles.

I'm not clear what the benefit would be to use a Jakyl bolt vs what I am doing now?

I think I saw that on your site before but had forgotten.  Can you weld an extension on top of the Geissele hammer to get more travel?  Adds weight, of course.

I have no desire to weld on a Geissele SSF.  I am still tinkering with various permutations and already have it running better than my full auto MP5 so don't really care if it is bottoming out or not.

Fair nuff.  Thanks for sharing all the tinkering you do.

Ready to try a rotary delayed blowback 5.56?  

I know you must be joking but seriously that would be a bad idea.
I think 10mm is already pushing the limits of the RDB system considering that it comes from the factory with the heaviest CMMG tuning weight installed in the carrier and I'm skeptical how much bigger they can make the angles on the bolt before it just won't rotate and then shear off like what I think would happen in 556.

Also, my 'Ultimax' setup in 556 is an absolute dream to shoot suppressed and un-suppressed.   I don't know what else I could do to make it better.  

Mill your own carrier.  

I do think radial delayed blowback would suffice for subsonic .300 Blackout, but all bets would be off with a Super in there.