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Originally Posted By zentradi: CMMG remains correct. The bolt is locked from rearward movement until it begins to rotate at which time the ramped area of the back of the bolt is in contact with the barrel lugs and the bolt glides smoothly over the barrel lugs. This is why I can stack weights against it, and the carrier must move first, to allow the rotation of the bolt. This is why the CMMG dissent sounds better suppressed than straight blowback guns. It is a very well-thought-out and timed action that allows for a smooth movement. The CMMG action is very well done. Unless you have the muscle fortitude of a weak pansy, there is hardly any recoil. A roller lock action such as an A3 Stribog does suppress better though, so I would love to see what CMMG could do to make a more inertia-driven action to further delay the movement of the bolt, because shooting unsuppressed guns is lame. I might custom make a bolt that has an increased flat area distance before ramp contact area, similar to the .40 bolt, to try and delay the unlocking further. The bolt does eventually move, it's not like a bolt or lever action that needs to be manually moved. Saying it doesn't lock because it moves means you don't get the whole semi-automatic repeating weapon idea. https://www.ar15.com/media/mediaFiles/14200/cmmg_contact_png-3314263.JPG  FUCK YES! PLEASE MAKE A CUSTOM BOLT WITH AN INCREASED FLAT AREA! I'll send you $87 if you do it. @amphibian made a custom 9x19mm bolt on one of his builds by filing a 5.45x39mm bolt. I'm sure he's got some tips. |
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Originally Posted By zentradi: CMMG remains correct. The bolt is locked from rearward movement until it begins to rotate at which time the ramped area of the back of the bolt is in contact with the barrel lugs and the bolt glides smoothly over the barrel lugs. This is why I can stack weights against it, and the carrier must move first, to allow the rotation of the bolt. This is why the CMMG dissent sounds better suppressed than straight blowback guns. It is a very well-thought-out and timed action that allows for a smooth movement. The CMMG action is very well done. Unless you have the muscle fortitude of a weak pansy, there is hardly any recoil. A roller lock action such as an A3 Stribog does suppress better though, so I would love to see what CMMG could do to make a more inertia-driven action to further delay the movement of the bolt, because shooting unsuppressed guns is lame. I might custom make a bolt that has an increased flat area distance before ramp contact area, similar to the .40 bolt, to try and delay the unlocking further. The bolt does eventually move, it's not like a bolt or lever action that needs to be manually moved. Saying it doesn't lock because it moves means you don't get the whole semi-automatic repeating weapon idea. https://www.ar15.com/media/mediaFiles/14200/cmmg_contact_png-3314263.JPG We are saying the bolt moves in relation to the barrel immediately as opposed to a locked breach gun in which the barrel and bolt either stay fixed in relation to each other upon firing. Your reference to the A3 Striborg as a "roller lock action" shows we have two entirely different definitions of a roller locked action. As Ian puts it, a roller lock firearm "differs from roller delayed firearm actions because a roller locked design requires a separate outside force to unlock the system. Typically this is a recoil operated force..." He then references the flat locking surfaces found on a roller locked gun in contrast to the angled surfaces of a roller delayed gun.  How Does It Work: Roller Delayed Blowback  How Does It Work: Roller Locking |
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Originally Posted By backbencher: FUCK YES! PLEASE MAKE A CUSTOM BOLT WITH AN INCREASED FLAT AREA! I'll send you $87 if you do it. @amphibian made a custom 9x19mm bolt on one of his builds by filing a 5.45x39mm bolt. I'm sure he's got some tips. I don't sell or advertise work on this site. I am not an industry partner. |
If you are putting a lot of effort into arguing with me, you are probably really just wasting your time, sorry.
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Originally Posted By OHBuckeyes: We are saying the bolt moves in relation to the barrel immediately as opposed to a locked breach gun in which the barrel and bolt either stay fixed in relation to each other upon firing. Your reference to the A3 Striborg as a "roller lock action" shows we have two entirely different definitions of a roller locked action. As Ian puts it, a roller lock firearm "differs from roller delayed firearm actions because a roller locked design requires a separate outside force to unlock the system. Typically this is a recoil operated force..." He then references the flat locking surfaces found on a roller locked gun in contrast to the angled surfaces of a roller delayed gun.  https://www.youtube.com/watch?v=sd8FrUe8fMM https://www.youtube.com/watch?v=68JQKznhjIYYou can't have a semi auto without moving parts. This is a stupid argument on your part and has no impact on what I have been saying, not even going further into this. You can go to the Stribog post in the armory pcc section and be told you are stupid there. |
If you are putting a lot of effort into arguing with me, you are probably really just wasting your time, sorry.
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CMMG has timed the perfectly that the bolt in the Dissent is locked from reward movement when it is forward, will slow the backward travel of the carrier as the released hammer is forward against the carrier. As mentioned before the rearward movement of the carrier allows the bolt to rotate and unlock for rearward travel. |
If you are putting a lot of effort into arguing with me, you are probably really just wasting your time, sorry.
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Originally Posted By zentradi: I don't sell or advertise work on this site. I am not an industry partner. Originally Posted By zentradi: Originally Posted By backbencher: FUCK YES! PLEASE MAKE A CUSTOM BOLT WITH AN INCREASED FLAT AREA! I'll send you $87 if you do it. @amphibian made a custom 9x19mm bolt on one of his builds by filing a 5.45x39mm bolt. I'm sure he's got some tips. I don't sell or advertise work on this site. I am not an industry partner. No, no, you misunderstand me, as usual. I will GIVE YOU $87 cash money if you make yourself a custom bolt for your CMMG radial DELAYED BLOWBACK and replace some of the angled surfaces of the bolt against the barrel extension lugs w/ flats. Make the bolt, send me pics via IM or post em up here before you go shoot it. I want you to have $87 cash in your hand before you go to the range. |
I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
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Originally Posted By zentradi: As mentioned before the rearward movement of the carrier allows the bolt to rotate and unlock for rearward travel. No. The bolt rotating as it’s forced back on the angle cut lugs is what moves the carrier to the rear. Yes a stronger action spring or hammer spring, or more buffer or carrier weight, will slow the action, but I’m not sure how much. Your comment on the StribogA3 being locked shows that you just haven’t wrapped your mind around the entire concept of delayed blowback operation. It’s very different than what you’re used to thinking about mechanically. It’s not personal, but you just don’t understand the operation. Try to watch some animations of a lever delayed system, those might help. |
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Here's probably an excellent explanation of ROLLER DELAY. Maybe this will help:  HK Director of Training Bob Schultz Unpacks The Roller Delayed Blowback System Sigh, not really. Should've watched it completely before I posted it. |
I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
Ok, HERE is a decent explanation of roller delay, followed by lever delay: Delayed Blowback System in Firearms Ian does a decent job of explaining CMMG's system w/o an animation:  CMMG Banshee: The Unique Radial Delayed Blowback System |
I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
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I think the issue is the short case. I think it rotates into the extension bolt lug space, then as the bolt travels to the rear, it gets pushed back toward the center by the extension lugs, then rotating again once past the extension and ejecting, fatiguing the ejector spring from multiple cycles per shot. |
| So in reading this thread and Amphibian's website, am I wasting my time trying to build a 9 MM PCC with the CMMG RDB setup? I've got a 9MM bolt/barrel combo ready to go with all the parts and my can is out of jail, but it seems that I need a degree in mechanical engineering to make this work. Or I just accept the fact that my spring might break between 300 and 1,000 rounds. |
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Originally Posted By netbrad: So in reading this thread and Amphibian's website, am I wasting my time trying to build a 9 MM PCC with the CMMG RDB setup? I've got a 9MM bolt/barrel combo ready to go with all the parts and my can is out of jail, but it seems that I need a degree in mechanical engineering to make this work. Or I just accept the fact that my spring might break between 300 and 1,000 rounds. The Dissent is very reliable and fixes the ejection issues but is not tune-able like the Banshee unless you do the custom machine work I have already posted about. Some don't care about tuning but you are fooling yourself if you think an out of the box Dissent or Banshee for that matter is MP5 smooth. Both are not. If you tune them, then they are both amazing. If you want it to be smoother than the typical straight blowback and accept the fact that it isn't MP5 smooth then the Dissent may be option for you. In my experience and everyone I know the ejector springs will 'fail' at around the 1K round mark with the Banshee. They don't 'break', they just wear out to the point that they are too weak to kick the brass out. I was going to reference a thread on here where two members here are saying they are like over 3K with no malfunctions. I guess these guys are lucky or something. That thread has aged out and I can't find it now. Most posts you see about people saying theirs runs great don't mention round count. If you already have the parts, I would run them. You may get lucky. I wouldn't rely on it though. If you really like it, maybe consider getting a spare bolt to leave in there with only a few rounds on it to make sure it is good. Then have your 'beater' bolt to run till failure. |
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Originally Posted By amphibian: Just to clarify, you are talking about the CMMG RDB Banshee which uses the spring loaded ejector in the bolt . The CMMG RDB Dissent is designed to use a fixed ejector. Both are RDB. The Dissent is very reliable and fixes the ejection issues but is not tune-able like the Banshee unless you do the custom machine work I have already posted about. Some don't care about tuning but you are fooling yourself if you think an out of the box Dissent or Banshee for that matter is MP5 smooth. Both are not. If you tune them, then they are both amazing. If you want it to be smoother than the typical straight blowback and accept the fact that it isn't MP5 smooth then the Dissent may be option for you. In my experience and everyone I know the ejector springs will 'fail' at around the 1K round mark with the Banshee. They don't 'break', they just wear out to the point that they are too weak to kick the brass out. I was going to reference a thread on here where two members here are saying they are like over 3K with no malfunctions. I guess these guys are lucky or something. That thread has aged out and I can't find it now. Most posts you see about people saying theirs runs great don't mention round count. If you already have the parts, I would run them. You may get lucky. I wouldn't rely on it though. If you really like it, maybe consider getting a spare bolt to leave in there with only a few rounds on it to make sure it is good. Then have your 'beater' bolt to run till failure. Thank you. I guess I should have clarified what I have. I have a 9MM bolt/barrel combo and I was going to use my own upper/lower/parts to build a PCC. The Dissent hadn't been released yet and I couldn't justify the price of the Banshee. Even adding your tuning parts like the hydraulic buffer I'll still come out way less than either a new Dissent or Banshee. I was going to maybe set it up for a home defense gun but it will likely be more of a range plinker. I won't be doing full auto. Someone had mentioned putting an O-ring from a BCM bolt repair kit somewhere in the mix but I can't find it. I don't know if its worth it to have the headspace slop removed like you did but I can't imagine that would be cheap (nor should it be). |
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Originally Posted By netbrad: Someone had mentioned putting an O-ring from a BCM bolt repair kit somewhere in the mix but I can't find it. Originally Posted By netbrad: Someone had mentioned putting an O-ring from a BCM bolt repair kit somewhere in the mix but I can't find it. I don't know if its worth it to have the headspace slop removed like you did but I can't imagine that would be cheap (nor should it be). |
I've got the initial Bolt and Barrel combo(5") and have approximately 1000+ rounds through it. I haven't noticed any issues with ejection, but I am honestly expecting it to happen sooner or later. I went ahead and purchased some replacement ejector springs for when that time comes. I built it using Amphibians 90% instructions(Tubbs 300blk spring, 5007 Hydraulic buffer, VLTOR a5 buffer tube) its ultra soft shooting and is a night an day difference when compared to the wife's AR-V. My personal opinion is go for it, build it up and enjoy shooting it, when it starts having ejection issues replace the faulty spring and start blasting some more  The springs are fairly cheap on CMMG's Website
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Here is an excellent illustration of lever-delayed blowback, showing the acceleration of the rearward bolt mass as the front of the bolt moves slowly: |
I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
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Originally Posted By backbencher: Here is an excellent illustration of lever-delayed blowback, showing the acceleration of the rearward bolt mass as the front of the bolt moves slowly: I really enjoy Serbu's videos. It's unfortunate Youtube has been so hostile to him, as he seems to be a pretty cool dude. |
Lovely diagrammed explanation between roller locking and roller delay: Roller Locking vs Delay: BotR Addendum To Ian's Forgotten Weapons Videos On The Topic |
I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
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I haven't been around in a while. I was going to start a new thread because I was messing with my 9mm bolt today, but saw this thread. I had the day off and decided to work on some projects that I had put aside. I dug through my pile of old forgotten projects and found the parts CMMG had sent me a while back (ejector spring, extractor spring, extractor buffer). I had reached out to CMMG the last time I had taken my 9mm AR to the range because the brass wasn't ejecting reliably and causing malfunctions. In the pile, I also found the bolt vice I had bought at some point to do the work. I have never taken the ejector out of a bolt before. I guess I never had a reason. The ejector was absolutely caked with crud in the cut-out area. The spring didn't come out very easy, I had to use a straightened paper clip to get it out. The spring looked more like a black pin than a spring because it was so dirty. I cleaned both as good as I could. I debated whether I should just reassemble everything now that it was clean and see if that fixed my issues, or go ahead and put the new parts in. In the end, I decided to put the new parts in. I was really hoping to hear that swapping the parts would fix the issue for good, but reading this thread, it doesn't sound like it. |
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Originally Posted By Joker23: I haven't been around in a while. I was going to start a new thread because I was messing with my 9mm bolt today, but saw this thread. I had the day off and decided to work on some projects that I had put aside. I dug through my pile of old forgotten projects and found the parts CMMG had sent me a while back (ejector spring, extractor spring, extractor buffer). I had reached out to CMMG the last time I had taken my 9mm AR to the range because the brass wasn't ejecting reliably and causing malfunctions. In the pile, I also found the bolt vice I had bought at some point to do the work. I have never taken the ejector out of a bolt before. I guess I never had a reason. The ejector was absolutely caked with crud in the cut-out area. The spring didn't come out very easy, I had to use a straightened paper clip to get it out. The spring looked more like a black pin than a spring because it was so dirty. I cleaned both as good as I could. I debated whether I should just reassemble everything now that it was clean and see if that fixed my issues, or go ahead and put the new parts in. In the end, I decided to put the new parts in. I was really hoping to hear that swapping the parts would fix the issue for good, but reading this thread, it doesn't sound like it. |
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Originally Posted By Alien: Yeah, it's really disappointing. CMMG understandably moved to the fixed ejector with their new guns, but they need to figure out what to do with the guns and parts they sold and fix that issue. Originally Posted By Alien: Originally Posted By Joker23: I haven't been around in a while. I was going to start a new thread because I was messing with my 9mm bolt today, but saw this thread. I had the day off and decided to work on some projects that I had put aside. I dug through my pile of old forgotten projects and found the parts CMMG had sent me a while back (ejector spring, extractor spring, extractor buffer). I had reached out to CMMG the last time I had taken my 9mm AR to the range because the brass wasn't ejecting reliably and causing malfunctions. In the pile, I also found the bolt vice I had bought at some point to do the work. I have never taken the ejector out of a bolt before. I guess I never had a reason. The ejector was absolutely caked with crud in the cut-out area. The spring didn't come out very easy, I had to use a straightened paper clip to get it out. The spring looked more like a black pin than a spring because it was so dirty. I cleaned both as good as I could. I debated whether I should just reassemble everything now that it was clean and see if that fixed my issues, or go ahead and put the new parts in. In the end, I decided to put the new parts in. I was really hoping to hear that swapping the parts would fix the issue for good, but reading this thread, it doesn't sound like it. Yeah, it's really disappointing. CMMG understandably moved to the fixed ejector with their new guns, but they need to figure out what to do with the guns and parts they sold and fix that issue. They have figured out what to do w/ the Mk 1, and they're doing it. They send out new springs, and sequentially label the fresh springs a new Mk # every few months. Mailing out cheap new springs (same as the old springs) is a helluva lot cheaper than recalling all those uppers, bolts, and carriers, and installing a fixed ejector in em that the carrier & bolts were never designed to accept. |
I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
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I finally got to the range today. I'm having mixed feelings. I shot 200 rounds suppressed, flawless. I decided to take the suppressor off and check for POI shift. *BANG* *click* Clear malfunction. *BANG* *click* Clear malfunction. *BANG* *click* Clear malfunction. This happened for 30 rounds, unsuppressed. On the one hand, I had zero issues with the suppressor on, so I'm thinking maybe I just need to clean it really good and try again. The additional back pressure may have given it just enough oomf to cycle. On the other hand, it was behaving exactly like it did before I replaced the ejector spring and extractor spring/buffer. I didn't bring my cleaning kit with me to the range, so I'm going to clean it really good this weekend and find out the next time I get a chance to go to the range. Has anyone else had an issue like this where their RDB was fine suppressed but failure to eject without the suppressor? |
| Put the suppressor back on and see if it cycles before doing anything. I would venture to guess the ejector tunnel is full of junk and the ejector spring is toast. Were the shot brass staying in the action? Gave up on mine and built a PSA AR-V with the left over bits. Runs like a top suppressed and with a Maxim Delayed buffer setup. |
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If I was a smart man, I would have put the suppressor back on and tried that before I left. The next live round was being stripped from the mag, but the empty brass was staying in the chamber, so the bolt couldn't go forward all the way. This was the first time I fired the rifle after replacing the parts CMMG sent (ejector spring, extractor spring and buffer). This was the first time I have ever replaced those parts, and it took me longer than expected. I may have done something incorrectly, but the first 200 rounds had no issues. It was only after taking the suppressor off that the issues started. Unfortunately, I don't get much free time anymore. Not sure when I'll get a chance to head back to the range. I've already decided that this upper is only a range toy so I'm not too concerned, more disappointed. |
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Haven't had a chance to get back to the range yet. I was thinking about this the other day and I remembered something. When I put the upper together, I used a regular AR upper. Back when I built it, some people were using uppers with larger ejection ports, some people were using standard uppers. I would think that if the issue was the size of the ejection port, I would have always had issues. After I first put it together, I had a few range sessions where it ran fine. After replacing the ejector spring and extractor spring and buffer, it initially ran fine. For other people that are having issues, did you use a regular upper or one with an enlarged ejection port? Edit to add - I just ordered an Aero XL receiver. I'll see if that helps or not. |
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Originally Posted By Joker23: It was only after taking the suppressor off that the issues started. Going to a fixed ejector eliminates all that and increases the operating window (as well as eliminates another wear item). As long as the bolt goes back far enough for the fixed ejector to hit the case, it is definitely getting kicked out. One of the guys I built a hybrid fixed ejector Dissent for is using a BRT ported barrel and the thing shoots so soft that it isn't bottoming out...he also reloads like me and needs to load accordingly for it to not bottom out. Of course he can always load hotter. |
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Both happy and sad to find this thread. I've been chasing reliability issues with my cmmg rdb for over a year. Finally got it going, made it through 12 mags without a hiccup, and then started getting failure to clear the ejection port with spent casing. Followed by a fed live round and a spent round trying to date in the chamber area. Installed BCM extractor upgrade, and now I get a malfunction every 1-3 rounds fired. Extractor overpowers the ejector spring, which is likely worn out after reading the posts here. My goal end point is the BRT cmmg rdb with MP5SD suppressor. Will try buffer spacer, A5, and improved ejector spring. |
I wouldn't say I'm a gun nut... but I'd consider extreme enthusiast.
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I reached out to CMMG support about my most recent issues with ejection - new round feeding, spent brass still in chamber. They sent me a new bolt marked 50. They also sent me an action tuning kit. Has anyone here used an action tuning kit with their RDB upper to address ejection issues? |
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Looks like CMMG finally did it.... https://cmmg.com/banshee  Advancing the Radial Delay Blowback System Website seems to indicate they will sell both versions though.... |
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Originally Posted By amphibian: Looks like CMMG finally did it.... https://cmmg.com/banshee https://www.youtube.com/watch?v=h00kUqu0J1EWebsite seems to indicate they will sell both versions though.... Great, so now we know there is no fix for the ar-style ejector issues... |
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Originally Posted By amphibian: Looks like CMMG finally did it.... https://cmmg.com/banshee https://www.youtube.com/watch?v=h00kUqu0J1EWebsite seems to indicate they will sell both versions though.... Did yer buddy sell them his ejector? Or have they been reading yer website? 
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I sell firearms produced by the finest child labor in the world, be it Filipino, Muslim, Mormon, Arizonan, or Texan.
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Originally Posted By backbencher: Did yer buddy sell them his ejector? Or have they been reading yer website? |
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The timing is amazing. I just got the new parts they sent me, and had email conversations with support about the ejection issue. I guess they wanted to keep the fixed ejector a secret until it was officially announced. I wonder if support will have any options for people that have been fighting the ejection issues for years, any kind of a trade in program or anything. |
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Originally Posted By amphibian: Looks like CMMG finally did it.... https://cmmg.com/banshee https://www.youtube.com/watch?v=h00kUqu0J1EWebsite seems to indicate they will sell both versions though.... Oh for goodness sake! Amphibian, I bet that is a bit justifying for you. You knew this stuff way before they got around to making this. They really should have brought you on board. I notice how much it looks like your work... |
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Originally Posted By Jmacken37: Oh for goodness sake! Amphibian, I bet that is a bit justifying for you. You knew this stuff way before they got around to making this. They really should have brought you on board. I notice how much it looks like your work... As you can see in my pictures below, I have probably the lightest 'BCG' for an AR9. I'm betting the new FE Banshee BCG will be around 17oz while I'm sitting at 9.5oz.   |
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