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BRT CAR-15 SD 9mm (Page 2 of 2)
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Originally Posted By amphibian: I need to test my new Scorpion mag lower setup. https://c3junkie.com/wp-content/uploads/2024/03/XK9-1.jpg this might be the solution! |
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Originally Posted By jt526: Looking forward to hearing how it goes, my cmmg bolt is off being milled for RLL and I am just not liking the mean arms mags. The wasted space just offends me for some reason. So this might be the solution! Originally Posted By jt526: Originally Posted By amphibian: I need to test my new Scorpion mag lower setup. https://c3junkie.com/wp-content/uploads/2024/03/XK9-1.jpg this might be the solution! That is why I went through so much trouble to make my hybrid Dissent full auto configuration which is extremely tune-able and I can actually keep full auto bursts on target easier with my build than my full auto MP5. It will also work with a RLL. |
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Originally Posted By tortilla-flats: No malfs after 50 total rounds. Off hand, 15 yards. 5 rounds each target. Flyers are on me; I suck. top left: WWB top right: AE lower left: Syntech https://www.ar15.com/media/mediaFiles/15341/20240327_134747-3171036.jpg Any update on function/accuracy? If you can, please to a group from a rest. Ugh, eagerly waiting for my barrel. Never thought I would get my suppressor before the barrel... |
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Originally Posted By tortilla-flats: No updates. Frankly, this is my lowest priority for shooting. I really don't have any practical use for it other than burning up what remains of my 9mm handloads. Were it not for the suppressor, I would have gotten rid of this build by now. Considering you're the one who started this thread, I am surprised by your lack of enthusiasm. It seems like you've only had this set up for a few days and you already want to get rid of it. Did it just not live up to your expectations? I doubt anyone (that is a civilian) has a practical application for this firearm. I certainly dont. I am curious just because I am waiting on my barrel from BRT. |
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Originally Posted By muzzleloader: Considering you're the one who started this thread, I am surprised by your lack of enthusiasm. It seems like you've only had this set up for a few days and you already want to get rid of it. Did it just not live up to your expectations? I doubt anyone (that is a civilian) has a practical application for this firearm. I certainly dont. I am curious just because I am waiting on my barrel from BRT. Now I'm stuck with it (due to the suppressor*). It'll sit in the back of my safe until I either get rid of it or I can find purpose for it. *I'm also currently stuck with a 308 suppressor I have no use for. Another poor decision. Both of those decisions are kinda eating at me, at the moment. That said, I am surprised at how pleasant it is to shoot and its more accurate than me. I might try to find a PCC match to shoot it in. |
Tom Sawyer.
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Originally Posted By amphibian: I need to test my new Scorpion mag lower setup. https://c3junkie.com/wp-content/uploads/2024/03/XK9-1.jpg 
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Who wants to be my friend?
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Originally Posted By amphibian: I need to test my new Scorpion mag lower setup. https://c3junkie.com/wp-content/uploads/2024/03/XK9-1.jpg Beautiful weapon there Amphibian. Seems NFA did away with their S-9 lowers. Quick check on the website turns up notta. Luckily I already have one, but I wanted to get another to build out a rifle for the wife. Wonder why they got rid of them? |
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Originally Posted By tawoodii: Beautiful weapon there Amphibian. Seems NFA did away with their S-9 lowers. Quick check on the website turns up notta. Luckily I already have one, but I wanted to get another to build out a rifle for the wife. Wonder why they got rid of them?I Originally Posted By tawoodii: Originally Posted By amphibian: I need to test my new Scorpion mag lower setup. https://c3junkie.com/wp-content/uploads/2024/03/XK9-1.jpg Beautiful weapon there Amphibian. Seems NFA did away with their S-9 lowers. Quick check on the website turns up notta. Luckily I already have one, but I wanted to get another to build out a rifle for the wife. Wonder why they got rid of them?I But based on this thread: https://www.ar15.com/forums/ar-15/New-NFA-S-9-Lower--Scorpion-mags---Pics--review-and-build-in-progress-with-CMMG-RDB/15-754694/ That guy got his working with the CMMG RDB so I figured, if I wait for Gen2 maybe the changes will make it more difficult with the CMMG RDB so might as well buy this one since the thread above was 'successful'. I purchased 10 of the same mags from Prepper Gun shop like he did (all clear version like his). I opened the package on 4 of the 10 and they all SUCK. I test fired it and it was jam city. I pulled the mag from the gun. Just stripping a round off with my thumb, it would hesitate for a few seconds and then the next round would move up. So obviously a mag problem. I checked the other 3 mags and they all the same shit. I thought maybe a COL issue. So I tried factory hollowpoints and just trying to strip rounds off with my thumb it would hesitate as well. Obviously not good enough for live fire. Since I opened the wrapper they wouldn't give me a refund which is bullshit. I can exchange them but why. To swap out for another shit one? I did return the other 6 for a refund but was also charged re-stocking fees. I'm not buying from them again. So I borrowed a factory CZ 30 and 20 round mag from a friend and I will need to clearance the carrier to make those work. I ordered some of the PSA AKV mags which people seem to rave about and got them today. They are like the CZ mags in that I will need to clearance the carrier for those also. I have uppers and carriers that have been clearanced to run unmodified AK mags like the KS47 stuff and those clear. So now I need to mill my upper and carrier out some more to test the factory CZ or PSA AKV mags. I did only buy two of the AKV mags this time and PSA literally put them both in saran wrap and a plastic mailer bag with no padding. What is more concerning is that a friend of mine bought one of these XK9 lowers at the same time and assembled his in a straight blowback configuration which is what it is designed for and even with factory CZ mags, it is jam city. He says it is feeding too low. Which is really what you need to make the CMMG RDB work....the feed height needs to be lower than straight blowback but I have shit mags right now so I don't know. So now my friend and I are wondering if these lowers are just whacked and don't work with either. Have you shot yours? |
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That's strange Amphibian. I wonder if they changed the feed geometry or mag angle going from an S-9 to that XK9 lower? My RDB S-9 will only feed well with PGS mags. I have about 8 of them in total. I've tried Magpul and they were a no go for both my AR-V and my S9. The AKV mags were a close second but I had to shave the plastic off the feed lips all the way down to the metal reinforcement and even then they induced malfunctions while feeding my S-9 lower. The PGS mags were the only ones that worked without issue out of the box. I will also admit I don't shoot much in the way JHPs with it, but I did test about 2-3 mags worth to make sure it would feed them well. If my memory serves me well there were a few hiccups with upward facing cartridges causing FTFeeds. It hated small projectiles like Hornady Critical defense, but liked Speer GDs and HSTs as long as they were heavy 135gr-150gr. I didn't notice anything cheesy about my ejector but the BHO is so simple it's kind of funny? I don't remember much pertaining to the ejector though as mine was pulled out when I put the CMMG guts in it. The BHO actuator is literally a piece of folded round metal held in by a small machine bolt and small flat piece of metal. It's chitzy as all hell but it does function without issue. To be honest when I built my S-9 I built it using your advice in the post you linked. I built it using a PSA KS47 upper instead of Gibbz or other NFA upper. I had some issue with the Bolt latch but I remedied it with some sandpaper work to the upper and to the posterior of the latch itself. I also built another 5" RDB upper that was mated to a now disassembled PSA Colt SBRed lower that I opened the magwell up some to accept modified Sterling SMG mags. I stopped toying with it though because I couldn't get LRBHO to work, I had a lot of fun building it though and may rebuild it again at another time. Below should be a picture of both. S-9 and modified Colt |
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Originally Posted By tawoodii: That's strange Amphibian. I wonder if they changed the feed geometry or mag angle going from an S-9 to that XK9 lower? My RDB S-9 will only feed well with PGS mags. Originally Posted By tawoodii: That's strange Amphibian. I wonder if they changed the feed geometry or mag angle going from an S-9 to that XK9 lower? My RDB S-9 will only feed well with PGS mags. I have about 8 of them in total. I've tried Magpul and they were a no go for both my AR-V and my S9. The AKV mags were a close second but I had to shave the plastic off the feed lips all the way down to the metal reinforcement and even then they induced malfunctions while feeding my S-9 lower. The PGS mags were the only ones that worked without issue out of the box. I will also admit I don't shoot much in the way JHPs with it, but I did test about 2-3 mags worth to make sure it would feed them well. If my memory serves me well there were a few hiccups with upward facing cartridges causing FTFeeds. It hated small projectiles like Hornady Critical defense, but liked Speer GDs and HSTs as long as they were heavy 135gr-150gr. If yours work then maybe I got a bad batch. My buddy ordered 4 at the same time I did and has the same issues so maybe we both have bad mags? I didn't notice anything cheesy about my ejector but the BHO is so simple it's kind of funny? I don't remember much pertaining to the ejector though as mine was pulled out when I put the CMMG guts in it. The BHO actuator is literally a piece of folded round metal held in by a small machine bolt and small flat piece of metal. It's chitzy as all hell but it does function without issue. To be honest when I built my S-9 I built it using your advice in the post you linked. I built it using a PSA KS47 upper instead of Gibbz or other NFA upper. I had some issue with the Bolt latch but I remedied it with some sandpaper work to the upper and to the posterior of the latch itself. I also built another 5" RDB upper that was mated to a now disassembled PSA Colt SBRed lower that I opened the magwell up some to accept modified Sterling SMG mags. I stopped toying with it though because I couldn't get LRBHO to work, I had a lot of fun building it though and may rebuild it again at another time. Below should be a picture of both. S-9 and modified Colt I'm doing another hybrid CMMG RDB 'PhaseII" build for one of the guys at the SMG match and he wants to run Colt mags so I need to test that again. Haven't touched that since I did it mentioned on my site: https://c3junkie.com/?page_id=374 One thing I never bothered to do was to weld on the bottom of the feed block to make a stop to prevent over insertion of the Colt mags. Video below is my old CMMG RDB setup using a modified 5.45 bolt with the custom fixed ejector.  9mm CMMG Guard and Colt mags |
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lol. I'm looking to run this setup in a PCC course. Just realized I have no sling for this. Not sure how to set one up; not seeing any attachment points on the upper at all. ETA: Actually, figured out a top rail sling attachment. |
Tom Sawyer.
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Originally Posted By tortilla-flats: lol. I'm looking to run this setup in a PCC course. Just realized I have no sling for this. Not sure how to set one up; not seeing any attachment points on the upper at all. ETA: Actually, figured out a top rail sling attachment. 
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Who wants to be my friend?
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Anyone know the weight of the BRT CAR-15 SD Handguard Assembly? 15.25 oz w/barrel nut, screws & shims I'm thinking of swapping out for a lighter weight setup. MI 7.25" Suppressor Rail is 9oz. ETA: Got a Smoke Composites 7.25" setup. 5.75 oz w/barrel nut & screws Aaannnddd, the barrel nut for the Smoke composites extends past the threads for the suppressors & barrel ports. |
Tom Sawyer.
"If The Rules bought us to this, what use are they?"
"If The Rules bought us to this, what use are they?"
Radial Delayed Blowback 9mm SBR w/MP5SD Suppressor (like CMMG Banshee) |
“The difference between treason and patriotism is only a matter of dates.”
"And how can man die better
Than facing fearful odds,
For the ashes of his fathers,
And the temples of his Gods."
"And how can man die better
Than facing fearful odds,
For the ashes of his fathers,
And the temples of his Gods."
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Looking to build one of these on a PSA 635 upper. Would the CMMG radial delay option or the straight blow back option be the better option? If going straight blow back, any recommendations on recoil mitigation? |
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Originally Posted By Little_Bo_Peep: Looking to build one of these on a PSA 635 upper. Would the CMMG radial delay option or the straight blow back option be the better option? If going straight blow back, any recommendations on recoil mitigation? |
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Originally Posted By jtb33: RDB SBR w/SD Suppressor https://live.staticflickr.com/65535/53555129540_fa684570fd_k.jpg Mp5 SDs use an o-ring at the base of the barrel. Do you need to use an o-ring for the brt SD? |
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Originally Posted By muzzleloader: Mp5 SDs use an o-ring at the base of the barrel. Do you need to use an o-ring for the brt SD? Originally Posted By muzzleloader: Originally Posted By jtb33: RDB SBR w/SD Suppressor https://live.staticflickr.com/65535/53555129540_fa684570fd_k.jpg Mp5 SDs use an o-ring at the base of the barrel. Do you need to use an o-ring for the brt SD? |
https://www.ArizonaShooting.org
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Originally Posted By JSchell1309: If anyone is ever looking to part ways with their SD RDB barrel, I need one. Been waiting months for BRT to restock them. Same here.... Back in November I asked him when they would restock and he told me to check back in 4 weeks. On Jan 25, I sent him another note asking for an update and that went unanswered. |
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Originally Posted By JSchell1309: If anyone is ever looking to part ways with their SD RDB barrel, I need one. Been waiting months for BRT to restock them. Just buy from RCM https://rimcountrymfg.com/product/rcm-ar9-sd-barrel/ Attached File |
"My friend, you would not tell with such high zest
To children ardent for some desperate glory,
The old Lie: Dulce et decorum est
Pro patria mori." -Wilfred Owen
To children ardent for some desperate glory,
The old Lie: Dulce et decorum est
Pro patria mori." -Wilfred Owen
Joined:
Feb 2025
Posts:
33
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FL, USA
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thats a blowback barrel, not RDB. but it with an scorpion mag lower would be pretty cool to get a more mp5 appearance. last i heard, the new setup uses an adapter to use regular 9mm cans and adds an expansion chamber so you dont have to use the HiTechArms mp5sd can, and supposedly the regular pistol cans work much better than the mp5sd can. i kinda regret ordering my suppressor like a month before he started testing this. my car15sd did not like Endomags. tried 3 Endomags with a milspec lower and it would fail to feed every few rounds. i have since gone with a CMMG colt mag lower and its pretty much resolved this issue and the mags look cool. only real downside is when mags are nearly fully loaded and bolt closed, its really hard to get it to lock in. i debated going to a glock mag lower, i been somewhat looked into Amphibians scorpion mag lower build but i dont think ill bother i swapped my BRT mp5sd handguard for a UTGPro SD handguard and while it no longer has the mp5sd look, i like the bigger handguard to cover my 12" suppressor. i did have to shorten the barrel nut, and the handguard dowsnt mount as secure as i like but im happy with it. with the 12" HTA suppressor, i get alot of gas in the face when rapid firing. ive done the RTV chargehandle mod, used a flatwire bufferspring but its still annoying. i have now changed the upper receiver to the GibbzArms sidecharging, i havent gotten to test it but im confident it will help eliminate gas to the face would be really cool if BRT could find someone to make a front charging SD handguard and use a Dissent internals. that and somebody making a scorpion mag lower for RDB and you would really have something that really takes over an mp5sd appearence |
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Originally Posted By Bye_Felicia: Just buy from RCM https://rimcountrymfg.com/product/rcm-ar9-sd-barrel/ https://www.ar15.com/media/mediaFiles/40084/Screenshot_2026-02-16_065447_png-3714161.JPG Appreciate it but like Kingfish said, that’s direct blowback and I’m looking for Radial Delay Blowback barrel that BRT makes now. I already have a 5” RDB upper, wanting to swap it to his barrel and SD adapter to run through a ton of bulk supersonic ammo I have. |
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Originally Posted By JSchell1309: Appreciate it but like Kingfish said, that’s direct blowback and I’m looking for Radial Delay Blowback barrel that BRT makes now. I already have a 5” RDB upper, wanting to swap it to his barrel and SD adapter to run through a ton of bulk supersonic ammo I have. Originally Posted By JSchell1309: Originally Posted By Bye_Felicia: Just buy from RCM https://rimcountrymfg.com/product/rcm-ar9-sd-barrel/ https://www.ar15.com/media/mediaFiles/40084/Screenshot_2026-02-16_065447_png-3714161.JPG Appreciate it but like Kingfish said, that’s direct blowback and I’m looking for Radial Delay Blowback barrel that BRT makes now. I already have a 5” RDB upper, wanting to swap it to his barrel and SD adapter to run through a ton of bulk supersonic ammo I have. Not the cheapest way to do it but have Amphibian convert it https://c3junkie.com/?product=modify-straight-blowback-barrel-to-the-cmmg-rdb-system-or-for-a-bolt-action-setup |
"My friend, you would not tell with such high zest
To children ardent for some desperate glory,
The old Lie: Dulce et decorum est
Pro patria mori." -Wilfred Owen
To children ardent for some desperate glory,
The old Lie: Dulce et decorum est
Pro patria mori." -Wilfred Owen
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Originally Posted By Bye_Felicia: Not the cheapest way to do it but have Amphibian convert it https://c3junkie.com/?product=modify-straight-blowback-barrel-to-the-cmmg-rdb-system-or-for-a-bolt-action-setup Originally Posted By Bye_Felicia: Originally Posted By JSchell1309: Originally Posted By Bye_Felicia: Just buy from RCM https://rimcountrymfg.com/product/rcm-ar9-sd-barrel/ https://www.ar15.com/media/mediaFiles/40084/Screenshot_2026-02-16_065447_png-3714161.JPG Appreciate it but like Kingfish said, that's direct blowback and I'm looking for Radial Delay Blowback barrel that BRT makes now. I already have a 5" RDB upper, wanting to swap it to his barrel and SD adapter to run through a ton of bulk supersonic ammo I have. Not the cheapest way to do it but have Amphibian convert it https://c3junkie.com/?product=modify-straight-blowback-barrel-to-the-cmmg-rdb-system-or-for-a-bolt-action-setup I know someone that has the Hitech / MEAN SD upper. He told me it is way too aggresively ported and it doesn't run even with hot 124Gr ammo. I sent him a picture of the RCM ported AR9 straight blowback barrel and he says the porting looks identical. He thinks the same company makes barrels for both. All that said, that amount of ported works fine for straight blowback but has issues with a delayed blowback setup. He ended up paying more money to have someone plug the ports of his upper to get it to work. When I tell people all these details, nobody wants to try paying me to convert one of those barrels. I personally don't care for these SD setups as it does have a smaller operating window. Here in FL factory Aguila 124 Gr is subsonic out of a 5" barrel. While factory 124Gr Blazer is supersonic. I do have a customer in a northern state that I did a 3.5" barrel for. I'm waiting to hear back from him but I may do more of those if he has success. |
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Finally caved in and back ordered the recent restock on the BRT website. @amphibian I already have a Gen 1 RDB BCG with the spring ejector. You think I should put the BRT barrel on that upper and Gen 1 BCG? Or is the Gen 2 BCG and fixed ejector an upgrade? I know you mentioned there is a lug angle difference between them. Think that would be noticeable in person and worth the downside of the Gen 1 using the weak ejector in the bolt face? Plan is to use his SD Hub adapter with a YHM R9 |
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Originally Posted By JSchell1309: Finally caved in and back ordered the recent restock on the BRT website. @amphibian I already have a Gen 1 RDB BCG with the spring ejector. You think I should put the BRT barrel on that upper and Gen 1 BCG? Or is the Gen 2 BCG and fixed ejector an upgrade? I know you mentioned there is a lug angle difference between them. Think that would be noticeable in person and worth the downside of the Gen 1 using the weak ejector in the bolt face? Plan is to use his SD Hub adapter with a YHM R9 However, like I mentioned before they are using the same 55 degree bolt that is used in the bufferLESS Dissent for the FE Banshee. Being bufferless means less reciprocating mass. There have been threads where people have issues running short barrels unsuppressed with the FE Banshee but then work fine when adding a suppressor. Likewise running an SD setup is going to have less backpressure. Analagous to an HK MP5SD which uses a 120 degree LP vs standard MP5 using a 100 degree or an MP5K suppressed using an 80 degree.... we have no options in changing bolt angles with the CMMG RDB at this time. So you are left with messing with buffers and springs. I get emails all the time asking me for advice on the BRT cycling issues. BRT already recommends using the LW Sprinco yellow spring and 3 oz carbine buffer. It is his product so I'd say do what he says and talk to him if it isn't working for you. I think that advice has worked for most people. You may have seen that I offer the service of lightening the carrier which should also help: https://c3junkie.com/?product=lighten-cmmg-fe-banshee-carrier-cut-key-in-half-and-provide-spacer-for-ars-ex  As you may know, I am the inventor of the MicroMOA Govnah adjustable gas block. Since I like tuning things I did this SD setup for the CMMG. See last sentence in my picture below. I'm saying adjustable gas but it is really adjustable porting but I guess you could say the same thing. This allows tuning the velocity and backpressure. Please don't ask me how I'm doing this as I am not ready to release it yet. I'm sure people will copy me once they see it. You have to zoom in but the average velocity was 1049Fps with this 115Gr Blazer brass. I'm very happy with how this came out being so compact and it is really quiet. Thing is so light that it feels like my son's airsoft gun. I don't care about HK MPSD compatibility and wanted to use a longer barrel nut that is common on some rails. This setup also uses a taper so nothing is coming loose.  |
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Originally Posted By amphibian: I think if you read through this thread you will see how much I despise the original spring loaded ejector and went through great lengths to modify it to use a custom fixed ejector. I was always hesitant to recommend the CMMG RDB for 9mm or .45 until the FE Banshee came out in Feb 2025. I wouldn't run the original spring loaded ejector if it was free. ... So you are left with messing with buffers and springs. I get emails all the time asking me for advice on the BRT cycling issues. BRT already recommends using the LW Sprinco yellow spring and 3 oz carbine buffer. It is his product so I'd say do what he says and talk to him if it isn't working for you. I think that advice has worked for most people. ... Yeah i been following your C3 website and your RDB evolution over time. Was always interested how you made your own fixed ejector and used 40SW bolt to play with lug angles. I'll likely use his barrel with the included fixed ejector upper and bolt. I currently have the Gen1 bolt and 5.5" cmmg barrel and am using your ARS setup you recommend. I chose a Tubb Flatwire and the RB5005 you recommend for use in a carbine tube. It's been super smooth running. I'll see how that 4.1oz 5005 buffer and tubb flatwire work with the CMMG gen 2 bolt and his BRT barrel and Hub adapter. May swap in a Ti firing pin to drop some mass up front too. Thanks for the advice. I may be coming to you for BCG lightening service if required. |
BRT CAR-15 SD 9mm (Page 2 of 2)
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