Warning

 

Close
Confirm Action

Are you sure you wish to do this?

Cancel Confirm
AR15.COM
AR Sponsor
8/15/2026 9:20:11 PM EDT
Some dude reached out to me saying he knows his shit with AR9s and told me this setup would be fine and “baller AF”:

Angstadt PCC Upper
Angstadt 0940 Lower
Kynshot Hydraulic Buffer RB5015HD
8.5” Long Buffer Tube
CMMG RDB Bolt & 5” Barrel
C3Junkie Custom Flat-Wire Spring

Angstadt states that their lower doesn’t work with radial delay. The dude said it’s just the ejector, so I took it off.

CMMG states that you need a standard ejection port for RDB. The dude said you don’t.

Curious if anyone has run a similar setup with success? I’m thinking the dude probably gave me terrible advice.

Should I get a different upper that supports RDB? Possibly a different receiver set? Or should I ditch RDB and go with DBB?
8/16/2026 8:05:37 AM EDT
[#1]
Sound like your ejector simply needs tweaking to get it to ride properly in it's carrier channel.
Now with more political fatigue.
8/16/2026 8:12:42 AM EDT
[#2]
Maybe ask the actual baller who uses radial delay in submachine gun matches:

@amphibian
8/16/2026 10:48:49 AM EDT
[#3]
Quote History
Originally Posted By osprey21:
Sound like your ejector simply needs tweaking to get it to ride properly in it's carrier channel.
View Quote
He is talking about the CMMG RDB system which has the ejector in the upper.  Sounds like you are thinking about a straight blowback 9mm AR that typically has the ejector in the lower.
8/16/2026 11:03:38 AM EDT
[#4]
Originally Posted By Rivz_96:
Some dude reached out to me saying he knows his shit with AR9s and told me this setup would be fine and "baller AF":

Angstadt PCC Upper
Angstadt 0940 Lower
View Quote
https://angstadtarms.com/product/0940-lower-receiver/  - Read the description: "Not compatible with the CMMG radial delayed system."....
Maybe it is fine when you remove the ejector?  I don't know.  I know some have posted that the FM9 Glock lowers work with the CMMG system once you remove the ejector.  I just use the stripped CMMG Glock lowers if I want to run Glock mags as everything works including LRBHO.





Kynshot Hydraulic Buffer RB5015HD
View Quote
I've never liked that buffer for the CMMG RDB system....I've always recommended the RB5007 as documented on my site here: https://c3junkie.com/?page_id=2757
Although if you read that link, you will see that recently collaborated with Kynshot on the new RB5000A5 which I think is better than the RB5007 and I have a few on my website now.

8.5" Long Buffer Tube

View Quote
That is referencing the JRC 8.5" long tube which again, I have referenced above and describe that configuration as the ARS-EX which is really just for people that like to tinker and go the extra effort of cutting the key in half for additional travel and want to also deal with the added complexity of adding a spacer to prevent the key from slamming into the lower.  If you are not the type of person that likes to tinker or have ADHD and don't want to read shit, then avoid this setup and just do the standard ARS.

CMMG RDB Bolt & 5" Barrel
View Quote
Sounds like you have the crappy old spring loaded ejector CMMG RDB setup that I have documented here: https://c3junkie.com/?page_id=221
I wouldn't run that if it was free.
Just failures waiting to happen.  That old setup also has an erratic ejection pattern and does require a full length ejection port.  CMMG also made the vertical height larger on their uppers to also make it bigger for the erratic ejection pattern.
In Feb 2025, they released the FE (Fixed Ejector) Banshee as well their retrofit kit which finally resolved the FTE issues.  Kit is comprised of a new BCG and new upper with the FE bolted in the upper.  I sell my barrels as well as the FE kits.  The factory CMMG barrels are also hit or miss.  https://c3junkie.com/?page_id=1882


C3Junkie Custom Flat-Wire Spring

View Quote
Yes, those are my springs that I had made that work well for the the CMMG system as well as 556.




Angstadt states that their lower doesn't work with radial delay. The dude said it's just the ejector, so I took it off.

View Quote
As I posted above that is possibly true but have no first hand experience with their lowers.



CMMG states that you need a standard ejection port for RDB. The dude said you don't.

View Quote
True for the crappy old spring loaded ejector not true if running the new FE.



Curious if anyone has run a similar setup with success? I'm thinking the dude probably gave me terrible advice.

Should I get a different upper that supports RDB? Possibly a different receiver set? Or should I ditch RDB and go with DBB?
View Quote
I love my CMMG RDB setups.  IMHO, they are the ONLY 9mm SMG that can be tuned to have a low full auto cyclic rate (less than 600RPM) AND low reciprocating mass (9oz lightened BCG and 3.7oz magnetic buffer).  MP5 has low mass but shoots too fast for my tastes.  Many open bolt 9mm SMG's can run in the 600s but then they have really heavy bolts.

Sign up to continue the discussion

Create a free account to share your thoughts, follow topics, and connect with the AR15.COM community.

Already a member? Sign In

AR Sponsor