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Posted: 3/31/2026 12:12:07 PM EDT
[Last Edit: GimmeLibertee][Edited]
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I just bought one of these AR9s, 8", 9mm, that I intend to run suppressed 100% of the time with a Rugged Sub9 can. What is the best buffer setup for this configuration? CMMG sells a tuning kit that comes with different weights that are installed into the BGC itself, but I don't really understand the advantage of this compared to a heavier buffer and/or spring. I also see a few companies selling hydraulic buffers designed specifically for this gun's radial delayed blowback system. If I were to go the hydraulic buffer route, would the CMMG tuning kit still be needed, and what buffer spring would be best? |
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Did you get the FE (Fixed Ejector) version or get the old spring loaded ejector version that fails? Link to my site: https://c3junkie.com/?page_id=2757 This setup is what Chesters Hobbies as the 'Wildcard' setup at the end of this video:  Ultimate 9mm PCC Comparison PART 2 | CMMG Dissent (CMMG Dissent vs Banshee vs Sig MPX vs MP5) This link discusses my history with the CMMG RDB and where I am today with the tinkering on it: https://c3junkie.com/?page_id=3168 You will see that I am not a fan of adding reciprocating mass. I never liked using the tuning kit. In fact, I am going the opposite direction and milling the carrier out to make it lighter. You will also see that I am experimenting with magnetic buffers right now as well. I am also collaborating with Kynshot with a couple new variations. However, what is pictured below and used in Chesters Hobbies video, has been used since 2017. Many people are using it.  This setup is pretty forgiving. I can take the suppressor off and it will run unsuppressed. I updated my site that I've had several people tell me that recent batches of the Warthog spring are too tight to fit over the 5007. I have a custom order of springs from them that I will guarantee will fit over the 5007. |
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Thanks for the info, I'll need to digest that. I just purchased a brand new Banshee MkGs, so it should have the fixed ejector. ETA: So if one isn't interested in swapping out receiver extensions, which KynSHOT buffer and spring do you think is the next best thing? Would the KynSHOT RB5000HP paired with a Springco Red still be a noticeable improvement? Also, it sounds like the CMMG BCG tuning kit probably isn't needed? |
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Originally Posted By GimmeLibertee: Thanks for the info, I'll need to digest that. I just purchased a brand new Banshee MkGs, so it should have the fixed ejector. ETA: So if one isn't interested in swapping out receiver extensions, which KynSHOT buffer and spring do you think is the next best thing? Would the KynSHOT RB5000HP paired with a Springco Red still be a noticeable improvement? Also, it sounds like the CMMG BCG tuning kit probably isn't needed? No, I wouldn't get the tuning kit. Also, just because it is brand new, don't assume you have the fixed ejector. There is a lot of new old stock out there. |
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Originally Posted By amphibian: Also, just because it is brand new, don't assume you have the fixed ejector. There is a lot of new old stock out there. So not all MkGs models have the fixed ejector? According to CMMG's website, these models use a "fixed ejector radial delayed blowback" operating system. I don't have the gun in hand yet... ETA: checked with my dealer, it is the "FE" model so GTG there. |
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Originally Posted By amphibian: If you want to stay with the carbine buffer tube, I would say use the Warthog flat spring (with the caveat I mentioned on my site, that recent batches are tight but I have some on order that will be custom and fit for sure) and the Kynshot RB5005....for today. I may say something different in a few weeks after doing some more testing. The only real difference I can tell from the specs when comparing the RB5005 to the RB5000HP, is that the RB5005 is 0.2 oz heavier (5.0 oz. vs. 4.8 oz.). However, it looks like from the info you provided on your site that the RB5000HP has a stiffer hydraulic? What then in your opinion is the disadvantage of running the RB5000HP, and why does KynSHOT specifically reccomemnd the RB5000HP for the CMMG RDB system? Are we really splitting hairs here or is there a considerable difference in how these perform? |
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Originally Posted By GimmeLibertee: The only real difference I can tell from the specs when comparing the RB5005 to the RB5000HP, is that the RB5005 is 0.2 oz heavier (5.0 oz. vs. 4.8 oz.). However, it looks like from the info you provided on your site that the RB5000HP has a stiffer hydraulic? What then in your opinion is the disadvantage of running the RB5000HP, and why does KynSHOT specifically reccomemnd the RB5000HP for the CMMG RDB system? Are we really splitting hairs here or is there a considerable difference in how these perform? |
| Unrelated, but I picked this up yesterday, and discovered that the fixed ejector will need to be temporarily removed in order to use a BEV Block or reaction rod to swap muzzle devices. Anybody know the recommended torque spec for the screws? I assume blue loctite is recomended? |
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Had a chance to put the first few rounds through this yesterday, wow, this gun is great. I wish I had bought one of these sooner, screw direct blowback. Hoping to get my Rugged Sub9 any day now. ETA: picked up the can today, life is good. 
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This gun is running pretty smoothly and reliably suppressed with a Rugged Sub9, KynSHOT RB5000HP buffer and Tubb flat spring. However, I am getting a ton of shit coming out of the ejection port. It's so bad that my buddy who shoots left-handed can hardly shoot it. It feels like getting sandblasted with unburnt powder. Is this to be expected? I thought that this radial delayed blowback system was supposed to be suppressor friendly. Not my experience at all so far. @amphian: would your "A5 recoil system" potentially help mitigate this ejection port gas issue? |
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