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CMMG fixed ejector kit not reliable with FRT (Page 1 of 2)
Posted: 11/17/2025 9:18:31 AM EDT
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A little too much to fit it all in the thread title, so here goes: I started out with a CMMG RDB bolt/barrel and upper receiver kit from several years ago. I installed my own handguard and built a lower for it. Barrel is 16in. H3 buffer and a tubbs flat wire buffer spring. It is their original style with the plunger style ejector. It ran fine for years semi auto, no real issues that I can remember. So fast forward to FRT's becoming legal again and I picked one up. It was a dairyland defense 3 position I got here from a member. It ran great for a couple hundred rounds, then started getting lots of failures to eject all the sudden. I found the ejector spring issues online and checked mine, sure enough, weak as hell. The new fixed ejector kits had just come out so I just went ahead and ordered one of those after reading the spring issue will come back. I got it, installed it, and it runs great in semi auto, no ejection issues at all. On forced reset, it kept choking. That was a few months ago. Long story short, I have not had enough time to fuck with it until now. So I drag it out, load it up and try again yesterday. Runs perfectly on semi, but chokes in forced reset. I can get between 1-2 rounds then a dead trigger with a live round in the chamber or empty chamber. I then swap the upper onto another lower I have with a rare breed 3 position in it. Same H3 buffer and tubbs spring. It too runs perfectly fine in semi, but chokes in forced reset. With the RB trigger, it has a dead trigger with a empty chamber, almost every time. I tried switching ammo with no change, either lower/trigger. I put the original lower back on it with the dairyland trigger, but I then swap out the buffer spring for a standard weight carbine spring. I can now get some 2-4 round bursts before it chokes. So now I am wondering, is is short stroking in forced reset? The tubbs flat wire spring has a little more tension than the standard carbine. I could notice the charging handle is easier to pull with the standard carbine spring in it. Should I try a H2 buffer? Or does anyone else have any other suggestions. |
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Originally Posted By gqllc: There is a guy on Reddit r/AR9 user name coonhound_11 running a broad river CMMG and it is great running with SS and H1. I have had SS and FRT and could never get them to run with the triggers. I believe people are having better luck with SS on CMMG I have plenty of people that have purchased RDB compatible barrels and uppers from me running them with SS's and FRT's. Most of the people are running the buffer tube / buffer and spring setup I run here: https://c3junkie.com/?page_id=2757 |
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Originally Posted By amphibian: That guy just reached out to me about slowing his down in 300BLK but I've never tried running subsonic 300BLK with the CMMG system. I have plenty of people that have purchased RDB compatible barrels and uppers from me running them with SS's and FRT's. Most of the people are running the buffer tube / buffer and spring setup I run here: https://c3junkie.com/?page_id=2757 Gonna have to bookmark that page for future reading when I have some free time. |
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My 9mm RDB Franken-gun ran pretty well with an Arizona Regulator 2-position MilSpec FCG. I found a regular CAR buffer and spring worked well, with a fast cyclic rate and very little muzzle rise due to the low reciprocating mass. Maybe try a lighter buffer? I just recently replaced the AZR2P with an AS Designs ARC Fire super selector. It ran two magazines just fine (same buffer and spring). An additional observation, maybe specific to my gun: With the original BCG, it ran my hand loaded reloads just fine, but when I switched to the new FE BCG/upper, I experienced several case head separations with the same reloads. I have no problems when I run factory ammo, so that’s what I am doing… MagTech steel case 115s shoot relatively accurately and are priced right. |
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Try an H2 buffer, like you mentioned. Might also try downloading your mag to 10 rounds in a 30 round mag. The fuller the mag, the more drag it places on the carrier at rearward movement. That may help give an indicator to what is going on. |
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I can see where you're coming from, 'cause I know where you've been and I can see where you're going 'cause I can see the direction you're headed in. I just don't know where the hell you're at right now.
I can see where you're coming from, 'cause I know where you've been and I can see where you're going 'cause I can see the direction you're headed in. I just don't know where the hell you're at right now.
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Originally Posted By ARKAR: Try an H2 buffer, like you mentioned. Might also try downloading your mag to 10 rounds in a 30 round mag. The fuller the mag, the more drag it places on the carrier at rearward movement. That may help give an indicator to what is going on. It will do the issue all the way down to when the mag is empty, so it does not appear to be related to how many are in the mag. I have a extra carbine buffer and some tungsten weights. I will "make" me a H2 buffer tonight and then test it this weekend. Sadly that is the soonest I will be able to try/test anything. I think I have a couple extra buffers, so I may test a standard buffer too just for shits and giggles. |
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I just went through this. I initially started with the CMMG bolt face ejector but started getting inconsistent ejection within 150 rounds so I purchased the external extractor "upgrade" kit from CMMG as I was tired of screwing around with it. On my first outing with the rifle, bolt face ejector system, I had the same thing. Two rounds and then a dead trigger. I tried four different magazines repeatedly with no luck and it was pretty consistent. I had one mag that I was able to get ten rounds out of initially and then it too would start doing the two shot freeze. Nothing I did at the range helped. I changed ammo as well to no avail. It basically came down to me having the wrong buffer system (Unrivaled dead blow lightweight version). I went back to a standard 3oz buffer and a Sprinco yellow spring. I can now mag dump. Last outing I used a standard push-style super safety (no levers) and it worked flawlessly (with a caveat). I previously had an Atrius which I believe is out of spec and while it worked initially, its since stopped working. The caveat is I was, as the same time, having bolt drag on the magazine feed lips and it would cause a misfeed. With mags that I optimized correctly, there was no bolt drag and the rifle functioned perfectly. The wrong buffer caused the two round then dead trigger where the mags caused misfeeds but probably contributed to my initial dead trigger issues as well. |
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Ok, I had some time to fool around with it today. It still had the standard carbine buffer spring in it. I took the H3 buffer out and just swapped in the standard carbine buffer. 3 steel weights, no tungsten. I loaded up a 30 round mag, fired 5 rounds semi auto to verify function then switched to frt. I fired what sounded like 3-4, then dead trigger, live round in the chamber. I pulled the charging handle back enough to reset the trigger and tried again. It emptied the rest of the mag. This thing is all over the place. It walks and wonders worse than my 16in 223 with a frt. I take the buffer out, take it back in the house and disassemble it and change it to a H1. Two steel and one tungsten. I put it in and give it a go. 5 rounds semi auto with no issue, and it then dumped the rest of the mag. Still just violent and all over the place. Had as hell to control. I take the carbine buffer spring out and put back in my tubbs flat wire spring. Same drill. 5 semi auto then did a mag dump. It seemed a little better with the tubbs flat wire back in it. Still hard as hell to control. If I get some time next weekend, I'm going to try changing it to a H2 and see what happens. See if it causes any issues with reliability and/or calms it a little more. So it seems the buffer was just too heavy and that was causing the issues. Funny how it ran with the H3 with the old spring ejector BCG. But I think I remember reading somewhere that the angle on the new fixed ejector bolts are different, possibly giving it more delay. |
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Originally Posted By Jeeps-And-Guns: But I think I remember reading somewhere that the angle on the new fixed ejector bolts are different, possibly giving it more delay. Picture from my site below for those that don't want to click or read: Note that this picture was taken before CMMG released the FE Banshee. They used the same bolt (#2) that they used for the Dissent which is bufferless. I think they didn't want to go through the trouble of making a 50 degree bolt for the new FE Banshee.  The CMMG Tuning Kit won't help as it just ADD's mass. While I think it needs to have mass removed since they went with a 55 degree bolt for some scenarios.  |
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Originally Posted By amphibian: I've posted this many times already. Here is another link to my site: https://c3junkie.com/?page_id=1733 Picture from my site below for those that don't want to click or read: Note that this picture was taken before CMMG released the FE Banshee. They used the same bolt (#2) that they used for the Dissent which is bufferless. I think they didn't want to go through the trouble of making a 50 degree bolt for the new FE Banshee. https://c3junkie.com/wp-content/uploads/2024/02/bolt-comparison2-1536x839.jpg The CMMG Tuning Kit won't help as it just ADD's mass. While I think it needs to have mass removed since they went with a 55 degree bolt for some scenarios. https://c3junkie.com/wp-content/uploads/2025/10/FE_Banshee9mmBCG-vs-PhaseII-weights.jpg That is where I read it. I just could not remember where. It was a long time ago I read that and could not remember the website. I'm guessing the steeper angle on the new fixed ejector bolt is what has caused the issue and the need for a lighter buffer. I wonder why it runs perfectly fine in semi auto with the H3 buffer, but only has issues with frt. Also, I recently got spoiled on forced reset by shooting my 20in A2 in 223 with rifle stock/buffer and a light muzzle brake. I could not believe how controllable it was. My 16in 223 carbine feels like riding a bucking bronco compared to the 20in A2. And the 9mm feels like riding a wild pissed off bull compared to my 16in 223 carbine. |
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Originally Posted By Jeeps-And-Guns: That is where I read it. I just could not remember where. It was a long time ago I read that and could not remember the website. I'm guessing the steeper angle on the new fixed ejector bolt is what has caused the issue and the need for a lighter buffer. I wonder why it runs perfectly fine in semi auto with the H3 buffer, but only has issues with frt. Also, I recently got spoiled on forced reset by shooting my 20in A2 in 223 with rifle stock/buffer and a light muzzle brake. I could not believe how controllable it was. My 16in 223 carbine feels like riding a bucking bronco compared to the 20in A2. And the 9mm feels like riding a wild pissed off bull compared to my 16in 223 carbine. Here is the info on my 5.56 setup. https://c3junkie.com/?page_id=1403 IMHO, it is easy to get a smooth 556 setup with muzzle brake with all the gas it has but some brakes can be really obnoxious. I have mine tuned to be smooth with even no brake mounted. This is accomplished with the buffer setup I already mentioned, appropriate sized gas port and I also leverage a large volume gas tube which increases the dwell time.   The Ultimate M16 by Amphibian! (The ROF is mint). This video shows it unsuppressed with just an ASR flash hider (not a muzzle brake) unsuppressed at the beginning.  M16 Ultimax Same buffer setup running in 9mm CMMG RDB setup w/ LW carrier |
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You seem to like the Kynshot RB5007 as I am seeing that pop up a lot on your site as I have been scrolling through it. Kida expensive for a buffer, is it really worth the price? I probably already know your answer. It's one of those things I would kinda really like to try it before I buy it. I have spent money on things that are supposed to be better, only to be disappointed. However, it is much heavier at 6 ounces, so would it even work for my carbine? I mean, I just had to drop it down to H1 weight to make it run. Their site says "If you are using a carbine buffer tube with a CMMG Radial Delayed Blowback Bolt Carrier Group, please use the RB5000HP" It weighs 4.8 ounces, so its more closer to a H2, which might still work, I just have to get the time to test it. Now maybe the RB5007 would be better for my 16in 223? Its a midlength gas, superlative gas piston conversion, H3 buffer, tubbs flat wire buffer spring, RB 3pos FRT. |
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Originally Posted By Jeeps-And-Guns: You seem to like the Kynshot RB5007 as I am seeing that pop up a lot on your site as I have been scrolling through it. Kida expensive for a buffer, is it really worth the price? I probably already know your answer. It's one of those things I would kinda really like to try it before I buy it. I have spent money on things that are supposed to be better, only to be disappointed. However, it is much heavier at 6 ounces, so would it even work for my carbine? I mean, I just had to drop it down to H1 weight to make it run. Their site says "If you are using a carbine buffer tube with a CMMG Radial Delayed Blowback Bolt Carrier Group, please use the RB5000HP" It weighs 4.8 ounces, so its more closer to a H2, which might still work, I just have to get the time to test it. Now maybe the RB5007 would be better for my 16in 223? Its a midlength gas, superlative gas piston conversion, H3 buffer, tubbs flat wire buffer spring, RB 3pos FRT. I explained in great detail why I like the 5007 over the other ones. Basically, I tried hard to go lighter and I found that with the heavier body and lighter spring of the 5007, it allowed that mass to go forward on the initial recoil impulse. The 5000HP has less mass and a stiffer internal spring so IMHO, it isn't as effective on the initial impulse which is what I try to minimize. If you look at all my high speed videos, I have achieved a state where the carrier doesn't bottom out but the hydraulic does get compressed some but not totally. If the spring is stronger like on the HP you will feel that impact more on the rearward stroke as well. I am also using the long JRC buffer tube to maximize the bolt stroke and to obtain this condition of the carrier not bottoming out while NOT adding too much reciprocating mass which IMHO, makes the gun bouncy. If you want to stay with a carbine buffer tube then yes, the configurations I recommend are not for you. Even my son at 13 could use my setups with the JRC tube and still have to extend the stock some. Same if using armor. I have never seen a scenario where I would need to completely collapse the buffer tube with the long JRC tube for actual shooting. I don't care about side folders vs a typical telescoping stock using the buffer tube for these reasons. I don't care about putting in a backpack. |
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Originally Posted By amphibian: That guy just reached out to me about slowing his down in 300BLK but I've never tried running subsonic 300BLK with the CMMG system. I have plenty of people that have purchased RDB compatible barrels and uppers from me running them with SS's and FRT's. Most of the people are running the buffer tube / buffer and spring setup I run here: https://c3junkie.com/?page_id=2757 Are the barrels the CMMG FE compatible type? If I am understanding correctly, the OP had it working with the original spring ejector but not working with the fixed ejector. I am waiting for BRT to offer his barrel porting for the CMMG FE system and use a FRT with an appropriate suppressor. So, I am interested. |
Words fall from your mouth like shit from ass.
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Originally Posted By Steamedliver: Are the barrels the CMMG FE compatible type? Originally Posted By Steamedliver: Are the barrels the CMMG FE compatible type? If I am understanding correctly, the OP had it working with the original spring ejector but not working with the fixed ejector. I am waiting for BRT to offer his barrel porting for the CMMG FE system and use a FRT with an appropriate suppressor. So, I am interested. |
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Originally Posted By Dakota_Don: The KynSHOTs are worth every penny. I'm running two of them. The last one I got was from Botach and it was under $100 shipped. More sales are coming up soon. |
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Originally Posted By amphibian: Did you read the link I put in my first post? I explained in great detail why I like the 5007 over the other ones. Basically, I tried hard to go lighter and I found that with the heavier body and lighter spring of the 5007, it allowed that mass to go forward on the initial recoil impulse. The 5000HP has less mass and a stiffer internal spring so IMHO, it isn't as effective on the initial impulse which is what I try to minimize. If you look at all my high speed videos, I have achieved a state where the carrier doesn't bottom out but the hydraulic does get compressed some but not totally. If the spring is stronger like on the HP you will feel that impact more on the rearward stroke as well. I am also using the long JRC buffer tube to maximize the bolt stroke and to obtain this condition of the carrier not bottoming out while NOT adding too much reciprocating mass which IMHO, makes the gun bouncy. If you want to stay with a carbine buffer tube then yes, the configurations I recommend are not for you. Even my son at 13 could use my setups with the JRC tube and still have to extend the stock some. Same if using armor. I have never seen a scenario where I would need to completely collapse the buffer tube with the long JRC tube for actual shooting. I don't care about side folders vs a typical telescoping stock using the buffer tube for these reasons. I don't care about putting in a backpack. I have been trying to read through it as I get time here and there, but there is a lot there and I am trying to work through it. I am hoping in the next couple days to be able to give it a full read. I have just been very busy. |
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Originally Posted By Steamedliver: If I am understanding correctly, the OP had it working with the original spring ejector but not working with the fixed ejector. Yes, that is correct. It was running fine forced rest with the H3 buffer with the old spring ejector BCG, then stopped running once I switched to the fixed ejector. With the fixed ejector, it ran perfectly fine in semi auto, just not forced reset. |
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Originally Posted By amphibian: Their is no difference between barrels used for the CMMG old spring loaded ejector and the new FE if that is what you are asking. My site discussing barrels (non-ported) https://c3junkie.com/?page_id=1882 Sounds like this thread may be of more interest to you: https://www.ar15.com/forums/AR-15/FTF-s-in-new-9mm-suppressed-PCC-setup/15-791599/ Thanks for the link. I mixed up for a moment. It’s the bolt and upper that are different with FE version, not the barrel. I knew that, just momentary lapse. Thanks. |
Words fall from your mouth like shit from ass.
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Originally Posted By amphibian: Did you read the link I put in my first post? I explained in great detail why I like the 5007 over the other ones. Basically, I tried hard to go lighter and I found that with the heavier body and lighter spring of the 5007, it allowed that mass to go forward on the initial recoil impulse. The 5000HP has less mass and a stiffer internal spring so IMHO, it isn't as effective on the initial impulse which is what I try to minimize. If you look at all my high speed videos, I have achieved a state where the carrier doesn't bottom out but the hydraulic does get compressed some but not totally. If the spring is stronger like on the HP you will feel that impact more on the rearward stroke as well. I am also using the long JRC buffer tube to maximize the bolt stroke and to obtain this condition of the carrier not bottoming out while NOT adding too much reciprocating mass which IMHO, makes the gun bouncy. If you want to stay with a carbine buffer tube then yes, the configurations I recommend are not for you. Even my son at 13 could use my setups with the JRC tube and still have to extend the stock some. Same if using armor. I have never seen a scenario where I would need to completely collapse the buffer tube with the long JRC tube for actual shooting. I don't care about side folders vs a typical telescoping stock using the buffer tube for these reasons. I don't care about putting in a backpack. Ok, I have read through most of your linked pages and I am a little confused. It seems to be a mix of 223 and 9mm/pcc stuff, making it a little hard to follow and keep dedicated to my 9mm carbine. Kinda a info overload. I see the JRC buffer tube used/mentioned a lot, but then also almost always see the mention of having to use spacers with it. I am a little confused by this, as why use the longer buffer tube if you are going to have to use spacers to take up the extra length you just added? Unless I overlooked the answer. I am not locked into the carbine buffer tube and would not care about changing it. I could care less about collapsing the stock. I mainly just used the carbine stock/buffer tube as it looks correct for 16in and shorter barrels. So if I were to get the JRC buffer tube and a RB5007, and use my current tubbs flat wire spring, would I need any spacers in the tube? Do you think it would run with that setup? I would hate to spend the money and it not run. |
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Well botach had the RB5007 on sale and had a black friday code on their site. I was able to get two of them for $181 after tax and shipping. I am willing to give them a try in this 9mm, and also curious to try the other in my 16in 223 AR15. Now should I get the A5 buffer tubes or the JRC buffer tubes? If I am reading it right, I may need spacers if using the JRC tube? |
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Originally Posted By Steamedliver: Thanks for the link. I mixed up for a moment. It's the bolt and upper that are different with FE version, not the barrel. I knew that, just momentary lapse. Thanks. |
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Originally Posted By Jeeps-And-Guns: Well botach had the RB5007 on sale and had a black friday code on their site. I was able to get two of them for $181 after tax and shipping. I am willing to give them a try in this 9mm, and also curious to try the other in my 16in 223 AR15. Now should I get the A5 buffer tubes or the JRC buffer tubes? If I am reading it right, I may need spacers if using the JRC tube? JRC is if you want to do the ARS-EX for extended stroke so that the carrier doesn't bottom out in the tube for the smoothest possible configuration. If you don't want to bother with spacers and don't care about chasing the smoothest possible setup, then I would recommend you do the regular 'ARS' mentioned in my link above and just use the A5 tube. I make custom 'Delrin' spacers for the ARS-EX setup....if you want to be cheap just use a few quarters and verify the 'key' doesn't hit the lower like demonstrated in my pics below. Another picture from my site below. Of course 1-4 are for 5.56 while 5 is the FE Banshee that I lightened and also cut the 'key' back to match the key on the Surefire carrier for extended stroke.  This picture shows the Surefire OBC and the Geiselle SSF which has a shorter hammer.  Milspec hammer:  As I have mentioned in my previous post I can use the same exact lower for my FE Banshee setup as well as 556 assuming I have my Surefire OBC in there. This picture also shows my latest testing. This is the least amount of reciprocating mass I've done with the CMMG RDB.   Custom FE Banshee with Miculek magnetic buffer I say this is a 'Miculek' buffer but it is actually an 'Omni Robusta MARRS' and Miculek bought the patent. But that was short lived and since most people don't know the history I'm just saying it is the Miculek buffer. I've had this thing for years and for some reason it didn't work in Full auto in 556 and I shelved it so I'm just now re-visiting it as I am continually trying to get the reciprocating mass down but also have a slow cyclic rate. This is a tad fast for me but I made a new spacer to allow the spring to use the length of the JRC tube but stop the carrier before the key can hit the lower or the carrier slipping in front of the SSF hammer...but I haven't tested it yet.  Trying to beat the smoothness of the MP5 is hard with only 9.3 ounces of reciprocating mass but the MP5 also shoots to fast for my tastes and is basically not tunable beyond changing the LP and already have a #28 in my full size MP5 in the video below.  Single - Double - UZI - MP5 - Phase2 |
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My 223 carbine has a superlative arms gas piston kit in it, and I am staying with it. However, I compared it to a standard carrier and it does allow increased travel.  I removed my buffer/spring and tried it and it will go in far enough to actually let the hammer get in front of the carrier. The trigger currently installed is a rare breed 3 position. I will be switching to a G$ SSA-E with a ARC-fire FRT once I get them back from ASD (there was some fitment issues). If I stop just before the hammer drops off the front of the carrier, I may still need to elongate the charging handle slot.  On the 9mm, it looks like you just chopped the "key" in half to shorten it and allow more bolt travel. I can do that. If I got the JRC tube, keep my tubbs spring, use the RB5007, and cut the carrier key like yours, do you think I would also need to lighten the carrier like you did? I would need to test it once I got all the parts to see if I will need spacers and how thick they would need to be. I think I am going to order two of the JRC tubes to start with. |
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Looks like the top of the key is probably going to hit your charging handle. Look at my picture again and pay attention to the back of the Griffin and Surefire key which are different to prevent that impact. My website shows that I milled out a steel CH to prevent that for use with the LWRC integral carrier.  |
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Originally Posted By Jeeps-And-Guns: On the 9mm, it looks like you just chopped the "key" in half to shorten it and allow more bolt travel. I can do that. If I got the JRC tube, keep my tubbs spring, use the RB5007, and cut the carrier key like yours, do you think I would also need to lighten the carrier like you did? Originally Posted By Jeeps-And-Guns: On the 9mm, it looks like you just chopped the "key" in half to shorten it and allow more bolt travel. I can do that. If I got the JRC tube, keep my tubbs spring, use the RB5007, and cut the carrier key like yours, do you think I would also need to lighten the carrier like you did? If you don't care about this level of tuning then don't bother with it . I would say don't bother with modifying the key either if you don't care. None of these mods are 'needed' . An exception would be if you are using weak ammo unsuppressed the 55 degree bolt may be too much delay especially when combined with the 5.9oz 5007. Or running a ported setup that bleeds a lot of gas and doesn't have enough back pressure. I have some customers running into theses scenarios and I have lightened setups that have fixed those issues for them. I like LIVE mass like 5007, most of the mass is in the body which moves. I would rather have the mass in a moving part of the buffer than dead mass in the carrier. i can always change buffers as needed. Llightening the carrier increases the operating window as I have mentioned it has fixed issues with people running weak ammo and ported setups. It is easy to add mass if necessary with buffers later. Taking away mass isn't as easy. I would need to test it once I got all the parts to see if I will need spacers and how thick they would need to be. |
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Originally Posted By amphibian: Looks like the top of the key is probably going to hit your charging handle. Look at my picture again and pay attention to the back of the Griffin and Surefire key which are different to prevent that impact. Yea I mentioned in my post I may need to elongate the slot in the charging handle. I have a couple spare ones I could mill out to test. |
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Originally Posted By Jeeps-And-Guns: Would you recommend a A5 instead? Originally Posted By Jeeps-And-Guns: Originally Posted By amphibian: You will need a spacer if using the J Would you recommend a A5 instead? |
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Originally Posted By amphibian: That is up to you. I want the smoothest possible with the most tuning options and still use a collapsible stock so I use the JRC for all my setups now. I cut spacers on my lathe and can flip them if I want more spring pressure Trying to see the spaces in the pictures. So do you make them to where there is a small flange and then a section sticks up inside the spring, kinda like how the buffer fits in the spring? Doing this would let the spring extend the whole length of the tube, and then just give a "bump stop" inside the spring. Or are they just a solid plug inside the tube that is the full diameter and also compresses the spring the same amount as the thickness? Having a lathe and mill, I can make either style. |
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Originally Posted By Jeeps-And-Guns: Trying to see the spaces in the pictures. So do you make them to where there is a small flange and then a section sticks up inside the spring, kinda like how the buffer fits in the spring? Doing this would let the spring extend the whole length of the tube, and then just give a "bump stop" inside the spring. Or are they just a solid plug inside the tube that is the full diameter and also compresses the spring the same amount as the thickness? Having a lathe and mill, I can make either style. |
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The buffers showed up last week, but I only just last night got the JRC buffer tubes. I installed the tube onto the 9mm and for now, I have simply stacked some quarters to take up the space. I have it to where with the buffer compressed, the rear movement of the bolt is at the same position as it was with the carbine tube and buffer. I hope to try it out this weekend to see how it goes. I have also ordered some 1in dia aluminum bar stock to make some spacers out of. Once it gets here and I get some time, I will make a spacer with a thin flange to allow the buffer spring to go the full length of the tube (minus the thickness of the flange) and then try it and compare how it does vs the stacked quarters compressing the springs. I will be interested in seeing how it all goes. I have also removed the crap-tastic dairyland defense frt I was running in it, and replaced it with a rare breed 3 pos. I just switched over my 223 carbine to a SSA-E with a ARC-fire, so I took the RB from it and put it in my 9mm. The dairyland would actually lock up the BCG if you squeezed the trigger too hard. I am so glad to be done with that thing. Then later on, once I get the 9mm working, I will start the testing on my 223 carbine. |
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The aluminum bar stock showed up thursday, and I was off work yesterday (friday). I also ended up copying what you did to your carrier and trimmed the "key". I actually took the one off my old spring ejector BCG and cut it, since that BCG is useless now. That way if it does not work out, I can put the original "key" back on. I measured and made a spacer from the aluminum bar stock. It ended up being only 1/2in thick. I did make it flanged, to let the spring extend as much as I could. The flange I made about 1/8in thick. And since I had free time, I went ahead and swapped on the JRC buffer tube onto my 223, and measured for it. Funny, it ended up being the exact same 1/2in thick spacer. This gave the BCG the most travel it could have without having to mod the charging handle. The 9mm ran fine on semi auto. Recoil impulse felt a little different, but it had been a week since I shot it. Forced reset was inconclusive. It seemed to have a pretty decent ROF, but I did have a few malfunctions. Had a few times it stopped and there was a empty chamber, still ammo in the mag. I am also now using a rare breed trigger where before I was using a diaryland defense (that sucked). I will do a little more shooting to see how it goes. I didn't get through any mags without at least a couple stoppages. Now the 223, again, semi auto ran fine. Recoil impulse honestly did not really feel any different. I tried it on forced reset and was having a lit of stoppages. I was getting a dead trigger with a live round in the chamber, and also a few times of no round in the chamber, just like the 9mm. I opened the gas block 3-4 clicks to give it more gas and it still would get a stoppage where the chamber was empty. This gun was running fine with the old carbine buffer tube and H3 buffer. So I removed the JRC buffer tube and reinstalled my original carbine buffer tube and H3 buffer. So I decided to give the RB5007 another try in 223. I have a 20 inch A2 with rifle stock and rifle buffer tube and buffer, tubbs flat wire spring. I have a G2S and a arc-fire in it and this thing runs flawlessly with it. I measure it, made me a spacer for it, and gave it a try. I shot one mag with the original buffer, flawlessly. I then put in the spacer and the RB5007. It started to malfunction. Dead trigger with a live round in the chamber and light strike, then a couple times with a empty chamber. I remove the spacer and put the rifle buffer back in it and it is back to running flawlessly. So as of right now, these kynshot buffers do not seem to like my 223 rifles. I have a few carbines/lowers, so I am going to do a test on the 9mm and set one up with a carbine buffer tube and make me a H1 and H2 buffer, tubbs flat wire spring, and then swap the upper between the one with the JRC tube and kynshot and the standard buffer setup so I can do a back to back compare and see how things go. |
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There are 3 different Tubb flat springs . LW/300BLk, standard 555 and 308. I would try the LW or the Neverwear Warthog. I find the Warthog works well with the 5007 for both 9mm and 556. I will also say, I don't have any experience with the RDB with a 16" barrel like you are running. Note that CMMG advertises two different bolts for 40SW if you are running a 5 or 8" barrel vs a 16" barrel. So different bolt angles for the 16". That is the old spring loaded ejector. Unfortunately there is only one bolt that will work for the FE 9mm Banshee. Im in Florida where FRT's are illegal so don't have first hand experience with them. That said, in a real M16, the carrier needs to go back further in Full vs semi. I don't know about FRT's. If you were running FA, I would suspect it isn't going back far enough |
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Originally Posted By amphibian: There are 3 different Tubb flat springs . LW/300BLk, standard 555 and 308. I would try the LW or the Neverwear Warthog. I find the Warthog works well with the 5007 for both 9mm and 556. I will also say, I don't have any experience with the RDB with a 16" barrel like you are running. Note that CMMG advertises two different bolts for 40SW if you are running a 5 or 8" barrel vs a 16" barrel. So different bolt angles for the 16". That is the old spring loaded ejector. Unfortunately there is only one bolt that will work for the FE 9mm Banshee. Im in Florida where FRT's are illegal so don't have first hand experience with them. That said, in a real M16, the carrier needs to go back further in Full vs semi. I don't know about FRT's. If you were running FA, I would suspect it isn't going back far enough The tubbs springs I am running are the standard 5.56 versions. I do have the 308 versions in my two DPMS G2 308's and are happy with them. I may look into one of the 300blk ones. However at this point I am waiting till after the first of the year to order anything else to try and let the holiday rush die down. What is different about it Vs the 5.56 version? Yes all mine are different types of forced reset triggers. It did cross my mind that this could be effecting the results as I know you are running true full auto, which can behave differently than forced reset. I have the 16in barrel on my 9mm as at the time I built the carbine, pistol braces were questionable and I did not want to screw with a tax stamp. I am just sticking with it now as I do not feel like buying another barrel, handguard, and replacing the stock with a brace. Sometimes I wish I had a high speed camera to watch these when firing to see what happens. |
See Blowback9's site: https://blowback9.wordpress.com/2023/03/03/flat-wire-spring-comparison/  2lbs less force with the bolt closed. Warthog is 1lb less |
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Alright, now the holiday season has died down, all the traveling and family stuff is over, I finally had some time to get back at it. I ordered the tubbs 300BO recoil spring and gave it a try today. I ran 10 rounds through it semi auto with no issues, switched to forced reset and dumped the remaining 20 rounds flawlessly. I then tried another 30 round mag and it dumped it perfectly, not a single hiccup. I then loaded up the remaining of the 100 rounds I had and they all ran perfectly. So in 100 rounds I did not have 1 single issue. No jams, no nothing. All except for the first 10 were mag dumped forced reset. So it seems that 300BO spring was the final touch to get it working. It does seem much more controllable now. Still not as nice as my 20 inch 223, but it is a lot better than it was. I can control it a lot better now than I could before. I do not know what the rate of fire is, but it is a nice even steady chugging along. Seems slower than it was with the old spring ejector BCG, but it is not a bad thing. So to recap what I have now: 16in barrel CMMG fixed ejector upper and BCG Tubbs 300 blackout buffer spring JRC buffer tube Kynshot RB5007 Cut the "key" on the BCG in half to allow more reward bolt travel (just like you did in the picture in post #27) Custom made spacer for the buffer tube to prevent over travel, while allowing the max amount of travel I can get. RB 3 position FRT. |
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Originally Posted By Jeeps-And-Guns: Alright, now the holiday season has died down, all the traveling and family stuff is over, I finally had some time to get back at it. I ordered the tubbs 300BO recoil spring and gave it a try today. I ran 10 rounds through it semi auto with no issues, switched to forced reset and dumped the remaining 20 rounds flawlessly. I then tried another 30 round mag and it dumped it perfectly, not a single hiccup. I then loaded up the remaining of the 100 rounds I had and they all ran perfectly. So in 100 rounds I did not have 1 single issue. No jams, no nothing. All except for the first 10 were mag dumped forced reset. So it seems that 300BO spring was the final touch to get it working. It does seem much more controllable now. Still not as nice as my 20 inch 223, but it is a lot better than it was. I can control it a lot better now than I could before. I do not know what the rate of fire is, but it is a nice even steady chugging along. Seems slower than it was with the old spring ejector BCG, but it is not a bad thing. So to recap what I have now: 16in barrel CMMG fixed ejector upper and BCG Tubbs 300 blackout buffer spring JRC buffer tube Kynshot RB5007 Cut the "key" on the BCG in half to allow more reward bolt travel (just like you did in the picture in post #27) Custom made spacer for the buffer tube to prevent over travel, while allowing the max amount of travel I can get. RB 3 position FRT. Did you lighten (mill out) the carrier as well? I assume you are using the MEAN Endomag Pmag inserts? I also just remembered you are running a 16" barrel which is going to have more bolt thrust than a short barrel so you probably don't want to mill the carrier. I don't have any interest in a 16" barrel but can see how it wouldn't be as smooth as a short barrel with this operating system. |
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Originally Posted By amphibian: Sounds good. Did you lighten (mill out) the carrier as well? I assume you are using the MEAN Endomag Pmag inserts? I also just remembered you are running a 16" barrel which is going to have more bolt thrust than a short barrel so you probably don't want to mill the carrier. I don't have any interest in a 16" barrel but can see how it wouldn't be as smooth as a short barrel with this operating system. Nope, I did not do any milling or weight reduction on the carrier. I only shortened the "key". I actually removed the faux gas key from my old spring ejector BCG and cut it, since that BCG is useless now. That way if it did not work out, I still had the original fixed ejector key I could reinstall. I went with 16in as back when I originally built this, pistol braces were still questionable and I did not want to screw around with a tax stamp. I figured 16in was the easiest. I do not really have any reason right now to go shorter on the barrel length. It's working now and I am not going to touch it. Now if I can just get my 22lr to run 
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Interesting. I bought a CMMG Banshee FE 5" barrel with a 9mm glock mag lower. I removed the factory muzzle device and installed a KVP ASR brake. Using a DTT cassette FRT, it ran right out of the box with 115gr ammo. When I added a suppressor (SiCo Hybrid 46) it started to have hammer down on loaded chamber. Moving to an H buffer fixed this. It also works suppressed with an H and H2 buffer using 147gr fmj subs. Still using the factory buffer spring. The H2 really slows the rate down for me to a slow 600-ish "chugga-chugga" but I prefer a little faster like 750-800 rpm. Just yesterday I got a Partisan Disruptor and swapped it in, and the hammer down on live round malfunctions reappeared. I tried both the H and H2 buffers. Everything ran fine with the DTT. i don't have an H3 to try. Just thought I'd add these data point to the discussion. Differences in barrel length, bullet weight, suppressor back pressure, and even brand of FRT all affect tuning. Change any one thing and it's back to the drawing board. Eventually I will make a quick reference chart for different ammo, suppressed and unsuppressed to know which buffer to use for which situation. But that will only apply to one barrel length and one trigger.  |
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Here is something interesting. This 9mm has been running with the rare breed 3 position. However the trigger pull sucks. So I bought a ARC-fire and a $G trigger and swapped it in. Semi auto was fine, but it refuses to run with that trigger in forced reset mode. I get anywhere from 1-4 rounds then it is a dead trigger, hammer is down. It could be either a live round in the chamber or a empty chamber. Even had a couple jams. I swapped the rare breed back in and it went back to running fine. I am disappointed, as I was hoping to have a better trigger pull than the RB. Now for the interesting and confusing part. So after I swapped the RB back in and verified it was back to running fine, I decided to just try something. I had a lower that I had been using with my 22lr dedicated build. It has a rave 140 and a atrius. It also has a H3 and a tubbs flat wire spring (standard, not the lighter 300bo one). I pin my 9mm upper on it and it actually ran great. ROF was a little quicker, but it ran fine with no jams, and no instances of a dead trigger. Forced reset seems to be a whole can of worms to get working. Funny how it would not run with the RB trigger, a H3 and tubbs spring once I swapped in the fixed ejector kit. However using the same style H3 buffer and spring with a rave 140 and a atrius seems to work fine. |
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So I ran my 9mm rdb upper on that same lower that has the rave 140 and atrius, as well as a standard carbine buffer tube, tubbs flat wire spring and H3 buffer. I ran 200 rounds through it today flawlessly. I actually like the slightly higher ROF from this setup as opposed to the kynshot buffer. Just for curiosity, I swapped in the 300bo tubbs spring and gave it a go. It did not like it and would have lots of failures to fire. I put the standard tubbs back in it and it went back to running fine. I am just going to leave this lower and upper together, not going to touch a thing. I am going to ditch the JRC buffer tubes and the kynshot buffers. The juice was not worth the squeeze with them. |
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Are you still running a 16" barrel? If so, you are the only person I know of to use a 16" barrel with an FRT / SS / RDIAS / FA etc... That said, I think the longer barrels have more bolt thrust. Notice how CMMG sells two different .40SW BCG's depending on the barrel length. https://cmmg.com/bolt-carrier-group-mkgs-40-s-w-60d https://cmmg.com/bolt-carrier-group-mkgs-40-s-w-16-barrel-compatible The first one is most likely a 60degree bolt based on what I have seen and posted before and is for 5" and 8" barrels while the 16" I suspect may be using a 67 degree bolt seen in the 10mm version. I know that is .40SW but I have seen similar scenarios w/ long 9mm RDB setups. I have a few customers running 16" setups but not with FRT's. Using them for competition and I think they run heavier buffer setups. Or running the magnetic buffer setups like seen here: https://www.reddit.com/r/ar15/comments/1qhgt94/low_mass_high_resistance_testing_the_miculek/ I know some competition shooters don't like the impulse of the hydraulic. I discuss some of this here as well: https://c3junkie.com/?page_id=3168 If you scroll to the bottom, you will see that I did my own magnetic buffer since the Miculek sheared apart on me. My magnetic is designed differently and has not failed. This setup is sitting at 12.7oz or reciprocating mass with the buffer being only 3.7oz while the Kynshot is at 5.9oz. I prefer it to the Kynshot for full auto. However, my buddy who is an LE instructor that is also a lefty says the prototype and RB5007 is better for slower shooting and being less gassy. However, we didn't test any low back pressure cans either. I am also using my magnetic with an A5 buffer tube as well. |
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Originally Posted By amphibian: Are you still running a 16" barrel? If so, you are the only person I know of to use a 16" barrel with an FRT / SS / RDIAS / FA etc... That said, I think the longer barrels have more bolt thrust. Notice how CMMG sells two different .40SW BCG's depending on the barrel length. https://cmmg.com/bolt-carrier-group-mkgs-40-s-w-60d https://cmmg.com/bolt-carrier-group-mkgs-40-s-w-16-barrel-compatible The first one is most likely a 60degree bolt based on what I have seen and posted before and is for 5" and 8" barrels while the 16" I suspect may be using a 67 degree bolt seen in the 10mm version. I know that is .40SW but I have seen similar scenarios w/ long 9mm RDB setups. I have a few customers running 16" setups but not with FRT's. Using them for competition and I think they run heavier buffer setups. Or running the magnetic buffer setups like seen here: https://www.reddit.com/r/ar15/comments/1qhgt94/low_mass_high_resistance_testing_the_miculek/ I know some competition shooters don't like the impulse of the hydraulic. I discuss some of this here as well: https://c3junkie.com/?page_id=3168 If you scroll to the bottom, you will see that I did my own magnetic buffer since the Miculek sheared apart on me. My magnetic is designed differently and has not failed. This setup is sitting at 12.7oz or reciprocating mass with the buffer being only 3.7oz while the Kynshot is at 5.9oz. I prefer it to the Kynshot for full auto. However, my buddy who is an LE instructor that is also a lefty says the prototype and RB5007 is better for slower shooting and being less gassy. However, we didn't test any low back pressure cans either. I am also using my magnetic with an A5 buffer tube as well. Yes, still running the 16in barrel. I do not own any other 9mm AR uppers/barrel lengths. Everything else 9mm I have are pistols. |
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Well shit, I jinxed myself. I was shooting it today and was doing some short bursts on some steel plates just having fun and at first I thought I ran out, as I could not pull the trigger, till I looked at the ejection port and the bolt was closed. I pull the mag and there is still ammo. I rack the charging handle and a live round comes out. I reload and the trigger is still locked. I clear it and open the upper up and look and everything looks fine, nothing out of place. I close it and tested. It dry fired fine. I load the mag and 1 shot and the trigger locks. I open it back up and everything looks fine. I try it again and get a few more shots and the trigger locks again. WTF. This time I open it and carefully look as I am opening it and I see the issue. The atrius lever is getting under the BCG. When I open it, it pops back forward. I try semi auto and it runs perfectly, I try frt and it locks the trigger, the lever gets under the bolt carrier. I get it inside and get checking over things. Lever moves fine, all selector positions work, nothing is loose, nothing broken that I can see. I get looking at the bolt carrier and notice the track for the buffer retainer pin seems wider than normal. I check and sure enough, the CMMG cutout for the buffer retainer pin is wider. Normal AR BCG measured .156, the CMMG one measured .189. I think what is happening is because the atrius lever moves side to side a little, it is right at the very edge of the cutout when in frt mode, and I think now with a little wear on things, it is slipping into that track and getting caught. I looked at the lever and there is just a tiny bit of peening on it. Very hard to take a picture of. I tried my best. This sucks as I was really enjoying it with the rave 140 and atrius. For now I have reinstalled the upper back onto the lower with the RB and the kynshot buffer while I explore options to remedy this.  
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CMMG fixed ejector kit not reliable with FRT (Page 1 of 2)
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