I did it. Fixed ejector RDB.

[TheColtCollector]

I know amphibian accomplished this or his gunsmith, but they didn’t share how to. Here’s I how i did it. The cmmg radial delayed blowback has always been a cool concept for me, but the ejector sucks balls. My friend ross’ bolt needed a fresh spring every 300 rounds or so and that’s just not acceptable by any means for full auto use. So I opted to do surgery on it, and I don’t have any formal training.

Here’s what I did.

1 cut a path the depth of the ejector the entire length of the bolt carrier and bolt to mid point of where the magazine would sit.this can be cut just about the locking lug adjacent to the ejector so no lugs are lost. The bolt must be clearanced 30 degrees as that back near the spring.
2 cut a hole in the side of the receiver
3 weld on an aluminum block to give some extra meat. The upper is too thin. for screws. Drill and tap 2 holes in this for #6 machine screws
4 mill an ejector out of stainless bar stock that fits in the width of the ejector channel.
5 weld on a plate to the back of the ejector so it can be screwed onto Aluminum side plate
6 there’s a lot of hand fitting with a dremel.

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[KickStand]

Man that’s TITS.
Reminds me of the S&W 76 ejector set up.


That will likely last.....

 

[strobro32]

Wow. Is the design that bad? Do the 45 and 10mm bolts need replacement that often? How do they charge 1700 for a gun that needs extractor springs that often?

 

[amphibian]

I know amphibian accomplished this or his gunsmith, but they didn’t share how to. Here’s I how i did it.

RIght, as I mentioned on my website, I worked on a piston operated 9mm upper with another C2 years ago and we gave up when we realized we would need a fixed ejector. He later did a fixed ejector after I had abandoned the project. I used his fixed ejector on my CMMG RDB but he told me I couldn't post pictures of it or go into details on it and I have honored his request.

https://c3junkie.com/?page_id=280

 

[amphibian]

Wow. Is the design that bad? Do the 45 and 10mm bolts need replacement that often?

The .45ACP doesn't have this issue. At least mine doesn't have the issue nor anyone I know or have I seen posts about it.
The 9mm/.40SW and 10mm all have the issue.

I detail what I think the root cause is on my website below and it is excessive headspacing.
https://c3junkie.com/?page_id=221

How do they charge 1700 for a gun that needs extractor springs that often?

Extractor spring isn't the problem, the ejector spring is.
As mentioned on my site, their ejector springs are proprietary, shorter than a standard spring but thicker gauge and different material. Retail is 1.99 each. So not bad.

I have the CMMG RDB in 9mm / .40SW and .45ACP. I am not going to bother with the fixed ejector for .40SW and don't have issues in .45ACP.

Ejector springs last about 1000 rounds for myself and friends I know. If it was 300 rounds, I would suspect the extension headspacing is extra sloppy and may need to get replaced by CMMG.

As I have illustrated in my video below, I think that if your barrel extracts the brass with no extractor installed and no suppressor mounted then you should get CMMG to replace the barrel. My early barrel was doing that and eating parts.

I showed them that video above and convinced them to replace my barrel. As I have two 9mm BCG/BBL combos early one did that but later one didn't. Same for my .40SW. It doesn't extract brass with no suppressor and no extractor.

 

[strobro32]

Thanks for the info. I was considering the CMMG 45.

That's a lot of work CC. Looking forward to seeing the long term results.

 

[SecondAmend]

Thanks for posting. Rather similar to, but more robust than what Olympic Arms (OA) did.
For those not familiar with the OA ejector design:
https://pdfpiw.uspto.gov/.piw?PageN...1=5520019.PN.%26OS=PN/5520019%26RS=PN/5520019

MHO, YMMV, etc. Be well.

 

[strobro32]

I had one of the OA 9mm uppers. I can't remember a single time a case failed to eject.

 

[SecondAmend]

I had one of the OA 9mm uppers. I can't remember a single time a case failed to eject.

That's a nice looking set up.
I've got an OA .45 ACP 16" bbl. upper and I have their special order full auto carrier in it for M16 use. Shoots very nice. I have not had any ejection failures either, but apparently, as the ejector is a spring that gets bent on every stroke of the bolt, over a long number of cycles, the ejector can fatigue and break. Some OA pistol caliber upper owners on ARFCOM have expressed dismay that replacement ejectors are no longer available.

 

[Jmacken37]

Colt Collector and Amphibian, thanks for the information.

CC, are you offering an upgrade service???

 

[TheColtCollector]

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[TheColtCollector]

I’m not sure if I want to. However could I even legally offer this service? I’m not a FFL. It would just be an upper, but it is a gun part. Sounds too messy

 

[Mackjack]

Very cool fix

 

[Jmacken37]

CC, how’s your upgrade with the fixed ejector working?

 

[TheColtCollector]

CC, how’s your upgrade with the fixed ejector working?

Good! I made 2. One for Ross who I experimented on and then one for myself. Now I will say this upper kinda blows without amphibians reccommended hydraulic buffer/spring/buffer tube. I can’t remember what they are offhand, but once I got all those (listed on his website) this thing has a similar mp5 smoothness to it. I milled hardened stainless bar stock to be precise ejectors so I can’t see any kind of deformation

 

[TheColtCollector]

I take back what I said. I did have one problem. Originally cut the channel so deep j notched the cam pin a little and the cam pin broke while I was firing it. Had to buy a new cam pin, I made my ejector just a little shorter on the grinder so it doesn’t touch the fresh cam pin. Ever since then it’s been 100%

 

[Jmacken37]

When you’re ready to go commercial let me know 😃

 

[amphibian]

I haven't tried this myself but this is very close to what I have:
https://www.midwestgunworks.com/page/mgwi/prod/bt-kit0012

That said, to do the fixed ejector you have to cut the slot where the cam pin hole is which is a weak point. I have hairline cracks in my 5.45x39 bolts that I modified for the fixed ejector and cut my own angles on the bolt lugs.
The CMMG RDB bolts are slightly thicker and I thought that my slotted .40SW bolt that I run in 9mm (for increased delay) would run fine but after several thousand rounds of full auto, it finally broke too.
I just slotted another .40SW bolt on my milling machine instead of doing it by hand like I did the first one and so I'm more precise on the mill. I went the bare minimum on the slot depth hoping this bolt will last longer but who knows.

You guys may have heard CMMG's new Dissent uses a fixed ejector. Here are some pics I stole off Youtube.
Note that they moved the cam pin further back to prevent the breakage I'm experiencing.

 

[Jrv8984]

CC how did you determine where to make your cut in the upper receiver?

 

[SecondAmend]

Somewhat ironically, it appears that a fixed ejector causes other parts to break, and thus require fixing.