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FWIW, the Olympic Arms (OA) PCCs had a unique ejector assembly where the ejector included an integral spring. The ejector would be pushed out of the bolt path by the bolt in the two inches of bolt travel from and towards the breech. During that two inches of aft and fore travel, the ejector would press against the bolt and add about three to three and a half ounces of effective fore/aft drag force upon the motion of the bolt. The downside was that the ejector/spring would eventually break. One could probably put together a separate lever and spring mechanism (with more parts than the OA assembly) that could fit into the allowable space and perform the same functions. As no slot in the bolt is needed, such a mechanism would provide maintained bolt integrity. MHO, YMMV, etc. |
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Originally Posted By SecondAmend: One could probably put together a separate lever and spring mechanism (with more parts than the OA assembly) that could fit into the allowable space and perform the same functions. As no slot in the bolt is needed, such a mechanism would provide maintained bolt integrity. |
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Originally Posted By amphibian: The MDP-9 has such a mechanism + delayed roller blowback. Again reviews have been spotty but I don't think it has ejection issues. Originally Posted By amphibian: Originally Posted By SecondAmend: One could probably put together a separate lever and spring mechanism (with more parts than the OA assembly) that could fit into the allowable space and perform the same functions. As no slot in the bolt is needed, such a mechanism would provide maintained bolt integrity. Good to know. Thanks for the info. |
| I think I got less than 300 rounds out of the 10mm ejector spring I put in my original Banshee. I found that Bexar Arms sells one made of Inconel X750 and emailed to ask if they had any experience with them in the Banshee design, but never heard back from them. They aren't cheap at $7.99 each, but I ordered 4 to try (I have 3 Banshee 9mm uppers). I will report back once I have run them. I plan to take measurements and keep track of round count. |
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Originally Posted By chevrofreak: I think I got less than 300 rounds out of the 10mm ejector spring I put in my original Banshee. I found that Bexar Arms sells one made of Inconel X750 and emailed to ask if they had any experience with them in the Banshee design, but never heard back from them. They aren't cheap at $7.99 each, but I ordered 4 to try (I have 3 Banshee 9mm uppers). I will report back once I have run them. I plan to take measurements and keep track of round count. |
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Originally Posted By DOG556: Ok. Are these issues still Ongoing? How many rounds before they appear? For what I see in the internet, it seems to be all over the place, some say it has been like since day 1 and they are disgusted and some say they have had thousands of rounds with no issues. |
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Originally Posted By amphibian: the current hole is already orientated between where you would be making two new holes......so I don't think a good idea... I'm really tired of dealing with these two setups where the ejector spring is basically absorbing some of the initial recoil impulse.....so as mentioned, I hope to be moving away from both systems once I get a prototype working which involves a totally different upper from the MEAN and CMMG. Originally Posted By amphibian: Originally Posted By peachy: Would it be possible to drill a second hole in the CMMG bolt and add a second ejector, similar to the DPMS G2 bolts? https://www.gunsite.co.za/content/wp-content/uploads/2014/05/DPMS-G2-bolt.png I'm really tired of dealing with these two setups where the ejector spring is basically absorbing some of the initial recoil impulse.....so as mentioned, I hope to be moving away from both systems once I get a prototype working which involves a totally different upper from the MEAN and CMMG. On top of that, I had friends talk to them at Shot Show as well as my direct correspondence and they were unwilling to sell me a spare trunion and basically any spare parts and everything in that upper is proprietary. I knew that modifying the Dissent would be an easier route than the MDP-9 but since I was never impressed with the out of box recoil impulse with the RDB, I thought giving the MDP-9 a try would be better. However since the MDP-9 route was a failure, I figured the Dissent was my only path forward. BTW, I stumbled across this Youtube video where this guy mentions the same thing about the Dissent not being tune-able and that his tuned Banshee was the smoothest.  Ultimate 9mm PCC Comparison PART 2 | CMMG Dissent (CMMG Dissent vs Banshee vs Sig MPX vs MP5) If you look at his old video's and comments, his tuned Banshee is my 'old' CMMG setup that I have documented here: https://c3junkie.com/?page_id=280 Here is a link to my site with what I did to get the Dissent to run full auto, re-use the buffer tube and with my custom 'CE - Carrier Extension' even more tune-able with less reciprocating mass than the stock Dissent or a CMMG Banshee: https://c3junkie.com/?page_id=1733   As mentioned on my site, this setup is 'sustainable' since CMMG will sell you the Dissent BCG now. Think about the MP5 and it's wear items like the rollers, extractor spring and locking pieces. With the CMMG RDB, it is just the barrel extension and lugs on the bolt.....I guess you could also say maybe the cam pin since it has to take a lot of stress. I'm at over 50K with my custom SS 9mm CMMG RDB barrel and it is still fine. I'm only 2K into the custom Dissent Hybrid setup but since the cam pin has been moved further back as pictured below, I don't anticipate the bolt from cracking like they have in my CMMG Banshee slotted bolts for my custom fixed ejector.  Video of Phase I and II in action.  Amphibian's Hybrid CMMG Dissent |
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Originally Posted By amphibian: Just wanted to post an update to my comments above. I initially got an Angstadt MDP-9 upper to test with to make it full auto capable and use the buffer tube. However, during the baseline testing before I made any modifications, one of the rollers broke (again running in the stock form). It took a long time for them to fix it and was told that the issue was the trunion was misaligned. I had seen a post on Reddit about someone saying one of the rollers broke as well but thought those issues were resolved by now. Apparently not. On top of that, I had friends talk to them at Shot Show as well as my direct correspondence and they were unwilling to sell me a spare trunion and basically any spare parts and everything in that upper is proprietary. I knew that modifying the Dissent would be an easier route than the MDP-9 but since I was never impressed with the out of box recoil impulse with the RDB, I thought giving the MDP-9 a try would be better. However since the MDP-9 route was a failure, I figured the Dissent was my only path forward. BTW, I stumbled across this Youtube video where this guy mentions the same thing about the Dissent not being tune-able and that his tuned Banshee was the smoothest.  https://www.youtube.com/watch?v=aKpO36Jw6koIf you look at his old video's and comments, his tuned Banshee is my 'old' CMMG setup that I have documented here: https://c3junkie.com/?page_id=280 Here is a link to my site with what I did to get the Dissent to run full auto, re-use the buffer tube and with my custom 'CE - Carrier Extension' even more tune-able with less reciprocating mass than the stock Dissent or a CMMG Banshee: https://c3junkie.com/?page_id=1733 https://c3junkie.com/wp-content/uploads/2024/02/new-cam-pin-relief-1024x291.jpg https://c3junkie.com/wp-content/uploads/2024/02/CE-Tests-1024x432.jpg As mentioned on my site, this setup is 'sustainable' since CMMG will sell you the Dissent BCG now. Think about the MP5 and it's wear items like the rollers, extractor spring and locking pieces. With the CMMG RDB, it is just the barrel extension and lugs on the bolt.....I guess you could also say maybe the cam pin since it has to take a lot of stress. I'm at over 50K with my custom SS 9mm CMMG RDB barrel and it is still fine. I'm only 2K into the custom Dissent Hybrid setup but since the cam pin has been moved further back as pictured below, I don't anticipate the bolt from cracking like they have in my CMMG Banshee slotted bolts for my custom fixed ejector. https://c3junkie.com/wp-content/uploads/2024/02/bolt-comparison2-1024x559.jpg Video of Phase I and II in action. https://www.youtube.com/watch?v=nbHiJvWyEFoOriginally Posted By amphibian: Originally Posted By amphibian: Originally Posted By peachy: Would it be possible to drill a second hole in the CMMG bolt and add a second ejector, similar to the DPMS G2 bolts? https://www.gunsite.co.za/content/wp-content/uploads/2014/05/DPMS-G2-bolt.png the current hole is already orientated between where you would be making two new holes......so I don't think a good idea... I'm really tired of dealing with these two setups where the ejector spring is basically absorbing some of the initial recoil impulse.....so as mentioned, I hope to be moving away from both systems once I get a prototype working which involves a totally different upper from the MEAN and CMMG. Just wanted to post an update to my comments above. I initially got an Angstadt MDP-9 upper to test with to make it full auto capable and use the buffer tube. However, during the baseline testing before I made any modifications, one of the rollers broke (again running in the stock form). It took a long time for them to fix it and was told that the issue was the trunion was misaligned. I had seen a post on Reddit about someone saying one of the rollers broke as well but thought those issues were resolved by now. Apparently not. On top of that, I had friends talk to them at Shot Show as well as my direct correspondence and they were unwilling to sell me a spare trunion and basically any spare parts and everything in that upper is proprietary. I knew that modifying the Dissent would be an easier route than the MDP-9 but since I was never impressed with the out of box recoil impulse with the RDB, I thought giving the MDP-9 a try would be better. However since the MDP-9 route was a failure, I figured the Dissent was my only path forward. BTW, I stumbled across this Youtube video where this guy mentions the same thing about the Dissent not being tune-able and that his tuned Banshee was the smoothest. https://www.youtube.com/watch?v=aKpO36Jw6koIf you look at his old video's and comments, his tuned Banshee is my 'old' CMMG setup that I have documented here: https://c3junkie.com/?page_id=280 Here is a link to my site with what I did to get the Dissent to run full auto, re-use the buffer tube and with my custom 'CE - Carrier Extension' even more tune-able with less reciprocating mass than the stock Dissent or a CMMG Banshee: https://c3junkie.com/?page_id=1733 https://c3junkie.com/wp-content/uploads/2024/02/new-cam-pin-relief-1024x291.jpg https://c3junkie.com/wp-content/uploads/2024/02/CE-Tests-1024x432.jpg As mentioned on my site, this setup is 'sustainable' since CMMG will sell you the Dissent BCG now. Think about the MP5 and it's wear items like the rollers, extractor spring and locking pieces. With the CMMG RDB, it is just the barrel extension and lugs on the bolt.....I guess you could also say maybe the cam pin since it has to take a lot of stress. I'm at over 50K with my custom SS 9mm CMMG RDB barrel and it is still fine. I'm only 2K into the custom Dissent Hybrid setup but since the cam pin has been moved further back as pictured below, I don't anticipate the bolt from cracking like they have in my CMMG Banshee slotted bolts for my custom fixed ejector. https://c3junkie.com/wp-content/uploads/2024/02/bolt-comparison2-1024x559.jpg Video of Phase I and II in action. https://www.youtube.com/watch?v=nbHiJvWyEFoamphibian, that is amazing work. Let me see if I can put your Phase 2 in layman's terms: 1) Took a heavy, but off the shelf 9mm upper, and cut the Dissent's rearward cam clearance; 2) Swiped your Dissent ejector or fabricated a copy & bolted it into the new upper; 3) Chopped the Dissent bolt carrier into an AR type stub, and fabricated aluminum & stainless extensions to bring it back to stock AR carrier length, allowing auto sears & binary triggers, as well as tuning w/ buffer weights; 4) Added a sprung reciprocating mass in the carrier extension with a hard stop to prevent overcompression of the spring; 5) Used all your previous tuning tricks of various AR buffer springs, buffer tube lengths, internal spacers, and hydraulic buffers from tuning your previous RDB Guard/Banshee. Is that a decent summary or did I miss something? I presume you'll be trying a Dissent .40 S&W bolt if they release one? |
Death to quislings.
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Originally Posted By backbencher: amphibian, that is amazing work. Let me see if I can put your Phase 2 in layman's terms: 1) Took a heavy, but off the shelf 9mm upper, and cut the Dissent's rearward cam clearance; Originally Posted By backbencher: amphibian, that is amazing work. Let me see if I can put your Phase 2 in layman's terms: 1) Took a heavy, but off the shelf 9mm upper, and cut the Dissent's rearward cam clearance; 2) Swiped your Dissent ejector or fabricated a copy & bolted it into the new upper;  3) Chopped the Dissent bolt carrier into an AR type stub, and fabricated aluminum & stainless extensions to bring it back to stock AR carrier length, allowing auto sears & binary triggers, as well as tuning w/ buffer weights;   4) Added a sprung reciprocating mass in the carrier extension with a hard stop to prevent overcompression of the spring; 5) Used all your previous tuning tricks of various AR buffer springs, buffer tube lengths, internal spacers, and hydraulic buffers from tuning your previous RDB Guard/Banshee. Is that a decent summary or did I miss something? Also wanted to stress that the 9mm Dissent bolt has 55 degree angles while the 9mm Banshee is 50. I'm presuming since the Dissent has less reciprocating mass. Doing PhaseII, I am able to get the reciprocating mass even with the buffer to be lighter than a factory Dissent config. 15.1oz (10.4 for the BCG/CE and another 4.7 for the RB5005) vs the 17.2 oz pictured above. So I am 5.8oz heavier than a full size MP5 BCG but the MP5 shoots too fast. I also did some experimenting with a Delrin buffer since now that I have a spring loaded CE weight to kill bolt bounce I don't need that in the buffer. I did that with a Troy PDW compact stock and it just isn't as smooth as using the Kynshot hydraulic. Again, the more compact you go, the less smooth. I think this holds true even when comparing a full size MP5 to an MP5K. I presume you'll be trying a Dissent .40 S&W bolt if they release one? I would say yes to the former and would probably do a hybrid .40SW Dissent as well since if I did the former, as it would involve buying a .40SW Dissent BCG anyways so I could easily just retire my .40SW Banshee for a hybrid Dissent. I can honestly say this is smoother than my MP5 and I can dump rounds in full auto on target with this better than I can my full auto MP5 and I have a nice tune-able cyclic rate from the 500's to 700's. |
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Originally Posted By amphibian: Yes Yes, using an APC Ejector since CMMG wouldn't sell me a spare Dissent fixed ejector. https://c3junkie.com/wp-content/uploads/2024/03/EjectorComparison-1024x439.jpg Yes, more details below for those too lazy to click on the link to my site. https://c3junkie.com/wp-content/uploads/2024/02/Dissent-Phase2-BCG-weight-1024x302.jpg https://c3junkie.com/wp-content/uploads/2024/02/Banshee-vs-Dissent-BCG-weight.jpg Yep pretty much. Also wanted to stress that the 9mm Dissent bolt has 55 degree angles while the 9mm Banshee is 50. I'm presuming since the Dissent has less reciprocating mass. Doing PhaseII, I am able to get the reciprocating mass even with the buffer to be lighter than a factory Dissent config. 15.1oz (10.4 for the BCG/CE and another 4.7 for the RB5005) vs the 17.2 oz pictured above. So I am 5.8oz heavier than a full size MP5 BCG but the MP5 shoots too fast. I also did some experimenting with a Delrin buffer since now that I have a spring loaded CE weight to kill bolt bounce I don't need that in the buffer. I did that with a Troy PDW compact stock and it just isn't as smooth as using the Kynshot hydraulic. Again, the more compact you go, the less smooth. I think this holds true even when comparing a full size MP5 to an MP5K. You mean running a .40SW Dissent bolt in 9mm like I was doing with my old Banshee build? Or you mean doing a hybrid Dissent build in .40SW? I would say yes to the former and would probably do a hybrid .40SW Dissent as well since if I did the former, as it would involve buying a .40SW Dissent BCG anyways so I could easily just retire my .40SW Banshee for a hybrid Dissent. I can honestly say this is smoother than my MP5 and I can dump rounds in full auto on target with this better than I can my full auto MP5 and I have a nice tune-able cyclic rate from the 500's to 700's. Originally Posted By amphibian: Originally Posted By backbencher: amphibian, that is amazing work. Let me see if I can put your Phase 2 in layman's terms: 1) Took a heavy, but off the shelf 9mm upper, and cut the Dissent's rearward cam clearance; 2) Swiped your Dissent ejector or fabricated a copy & bolted it into the new upper; https://c3junkie.com/wp-content/uploads/2024/03/EjectorComparison-1024x439.jpg 3) Chopped the Dissent bolt carrier into an AR type stub, and fabricated aluminum & stainless extensions to bring it back to stock AR carrier length, allowing auto sears & binary triggers, as well as tuning w/ buffer weights; https://c3junkie.com/wp-content/uploads/2024/02/Dissent-Phase2-BCG-weight-1024x302.jpg https://c3junkie.com/wp-content/uploads/2024/02/Banshee-vs-Dissent-BCG-weight.jpg 4) Added a sprung reciprocating mass in the carrier extension with a hard stop to prevent overcompression of the spring; 5) Used all your previous tuning tricks of various AR buffer springs, buffer tube lengths, internal spacers, and hydraulic buffers from tuning your previous RDB Guard/Banshee. Is that a decent summary or did I miss something? Yep pretty much. Also wanted to stress that the 9mm Dissent bolt has 55 degree angles while the 9mm Banshee is 50. I'm presuming since the Dissent has less reciprocating mass. Doing PhaseII, I am able to get the reciprocating mass even with the buffer to be lighter than a factory Dissent config. 15.1oz (10.4 for the BCG/CE and another 4.7 for the RB5005) vs the 17.2 oz pictured above. So I am 5.8oz heavier than a full size MP5 BCG but the MP5 shoots too fast. I also did some experimenting with a Delrin buffer since now that I have a spring loaded CE weight to kill bolt bounce I don't need that in the buffer. I did that with a Troy PDW compact stock and it just isn't as smooth as using the Kynshot hydraulic. Again, the more compact you go, the less smooth. I think this holds true even when comparing a full size MP5 to an MP5K. I presume you'll be trying a Dissent .40 S&W bolt if they release one? I would say yes to the former and would probably do a hybrid .40SW Dissent as well since if I did the former, as it would involve buying a .40SW Dissent BCG anyways so I could easily just retire my .40SW Banshee for a hybrid Dissent. I can honestly say this is smoother than my MP5 and I can dump rounds in full auto on target with this better than I can my full auto MP5 and I have a nice tune-able cyclic rate from the 500's to 700's. I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits. If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance? Could you mill a complete aluminum unitary bolt carrier, or would the cam pin loads just wreck that? If you were to slot the right side of the upper & screw in a fixed bolt handle into the front of the carrier, could you come close to a constant recoil system in auto? |
Death to quislings.
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Originally Posted By backbencher: I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits. If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance? Originally Posted By backbencher: I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits. If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance? I didn't want to go too thin on the Al CE as I was concerned about strength which is also why I copied the Surefire OBC carrier dimensions at the top to give it more strength. Could you mill a complete aluminum unitary bolt carrier, or would the cam pin loads just wreck that? If you were to slot the right side of the upper & screw in a fixed bolt handle into the front of the carrier, could you come close to a constant recoil system in auto? |
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Originally Posted By amphibian: I thought about that but I purposely bored out the CE to utilize common AR buffer weights that everyone has access to vs custom weights. I didn't want to go too thin on the Al CE as I was concerned about strength which is also why I copied the Surefire OBC carrier dimensions at the top to give it more strength. Yeah...highly doubt that would go well. You lost me there. You want to add more mass Originally Posted By amphibian: Originally Posted By backbencher: I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits. If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance? I didn't want to go too thin on the Al CE as I was concerned about strength which is also why I copied the Surefire OBC carrier dimensions at the top to give it more strength. Could you mill a complete aluminum unitary bolt carrier, or would the cam pin loads just wreck that? If you were to slot the right side of the upper & screw in a fixed bolt handle into the front of the carrier, could you come close to a constant recoil system in auto? You lost me there. You want to add more mass No - I want to remove the greebles on the top of the bolt carrier so the bolt carrier can go farther back into the receiver extension, lowering the impact on the buffer tube buffer cap. Why the Ultimax light machinegun is so smooth - the bolt carrier never bottoms out, all the energy is absorbed by the recoil spring, slowing the bolt carrier to a stop, then pushing it forward. |
Death to quislings.
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Originally Posted By backbencher: No - I want to remove the greebles on the top of the bolt carrier so the bolt carrier can go farther back into the receiver extension, lowering the impact on the buffer tube buffer cap. Why the Ultimax light machinegun is so smooth - the bolt carrier never bottoms out, all the energy is absorbed by the recoil spring, slowing the bolt carrier to a stop, then pushing it forward. Originally Posted By backbencher: Originally Posted By amphibian: Originally Posted By backbencher: I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits. If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance? I didn't want to go too thin on the Al CE as I was concerned about strength which is also why I copied the Surefire OBC carrier dimensions at the top to give it more strength. Could you mill a complete aluminum unitary bolt carrier, or would the cam pin loads just wreck that? If you were to slot the right side of the upper & screw in a fixed bolt handle into the front of the carrier, could you come close to a constant recoil system in auto? You lost me there. You want to add more mass No - I want to remove the greebles on the top of the bolt carrier so the bolt carrier can go farther back into the receiver extension, lowering the impact on the buffer tube buffer cap. Why the Ultimax light machinegun is so smooth - the bolt carrier never bottoms out, all the energy is absorbed by the recoil spring, slowing the bolt carrier to a stop, then pushing it forward. I can remove the rear 'stud' on the back of the carrier now to gain another 1/2" of travel before the cam pin would hit the lower....but that isn't the issue....I can really only do about 1/4" otherwise the hammer will slip in front of the carrier like this:  Also bear in mind that in my old CMMG RDB setup I had my carrier machined to go deeper into the buffer tube and cut the key back to use a single bolt as shown below. That configuration was not reliable so I went back to the RB5007.  Now with the hybrid Dissent I'm finding that I am liking the RB5005 more than the RB5007. I'm only 2K into the hybrid Dissent and still have a few more permutations I want to try and then may try to see what happens if I gain a 1/4" in travel with the Geissele SSF and I can get more with a Milspec hammer. |
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Originally Posted By amphibian: Oh, yeah. Don't know if you've seen that I was able to get 5.56 not bottom out like the Ultimax here: https://c3junkie.com/?page_id=1403 I can remove the rear 'stud' on the back of the carrier now to gain another 1/2" of travel before the cam pin would hit the lower....but that isn't the issue....I can really only do about 1/4" otherwise the hammer will slip in front of the carrier like this: https://c3junkie.com/wp-content/uploads/2023/06/SSF-OBC-1024x523.jpg Also bear in mind that in my old CMMG RDB setup I had my carrier machined to go deeper into the buffer tube and cut the key back to use a single bolt as shown below. That configuration was not reliable so I went back to the RB5007. https://c3junkie.com/wp-content/uploads/2020/06/300BLK-A5-RB5005-40SWBolt-NoCan-1024x525.jpg Now with the hybrid Dissent I'm finding that I am liking the RB5005 more than the RB5007. I'm only 2K into the hybrid Dissent and still have a few more permutations I want to try and then may try to see what happens if I gain a 1/4" in travel with the Geissele SSF and I can get more with a Milspec hammer. Originally Posted By amphibian: Originally Posted By backbencher: Originally Posted By amphibian: Originally Posted By backbencher: I think I got most of the overview from your site, I've followed your experiments for quite some time and I'm terribly pleased you found a way to use the Dissent bolt & carrier with more standard AR bits. If you were to drill out the interior of your aluminum carrier extension, could you get to a lighter reciprocating mass or have a larger sprung weight with more travel distance? I didn't want to go too thin on the Al CE as I was concerned about strength which is also why I copied the Surefire OBC carrier dimensions at the top to give it more strength. Could you mill a complete aluminum unitary bolt carrier, or would the cam pin loads just wreck that? Yeah...highly doubt that would go well. If you were to slot the right side of the upper & screw in a fixed bolt handle into the front of the carrier, could you come close to a constant recoil system in auto? You lost me there. You want to add more mass No - I want to remove the greebles on the top of the bolt carrier so the bolt carrier can go farther back into the receiver extension, lowering the impact on the buffer tube buffer cap. Why the Ultimax light machinegun is so smooth - the bolt carrier never bottoms out, all the energy is absorbed by the recoil spring, slowing the bolt carrier to a stop, then pushing it forward. Oh, yeah. Don't know if you've seen that I was able to get 5.56 not bottom out like the Ultimax here: https://c3junkie.com/?page_id=1403 I can remove the rear 'stud' on the back of the carrier now to gain another 1/2" of travel before the cam pin would hit the lower....but that isn't the issue....I can really only do about 1/4" otherwise the hammer will slip in front of the carrier like this: https://c3junkie.com/wp-content/uploads/2023/06/SSF-OBC-1024x523.jpg Also bear in mind that in my old CMMG RDB setup I had my carrier machined to go deeper into the buffer tube and cut the key back to use a single bolt as shown below. That configuration was not reliable so I went back to the RB5007. https://c3junkie.com/wp-content/uploads/2020/06/300BLK-A5-RB5005-40SWBolt-NoCan-1024x525.jpg Now with the hybrid Dissent I'm finding that I am liking the RB5005 more than the RB5007. I'm only 2K into the hybrid Dissent and still have a few more permutations I want to try and then may try to see what happens if I gain a 1/4" in travel with the Geissele SSF and I can get more with a Milspec hammer. I think I saw that on your site before but had forgotten. Can you weld an extension on top of the Geissele hammer to get more travel? Adds weight, of course. |
Death to quislings.
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Originally Posted By backbencher: I think I saw that on your site before but had forgotten. Can you weld an extension on top of the Geissele hammer to get more travel? Adds weight, of course. |
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Originally Posted By amphibian: I have no desire to weld on a Geissele SSF. I am still tinkering with various permutations and already have it running better than my full auto MP5 so don't really care if it is bottoming out or not. Originally Posted By amphibian: Originally Posted By backbencher: I think I saw that on your site before but had forgotten. Can you weld an extension on top of the Geissele hammer to get more travel? Adds weight, of course. I have no desire to weld on a Geissele SSF. I am still tinkering with various permutations and already have it running better than my full auto MP5 so don't really care if it is bottoming out or not. Fair nuff. Thanks for sharing all the tinkering you do. Ready to try a rotary delayed blowback 5.56? 
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Death to quislings.
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Originally Posted By backbencher: Ready to try a rotary delayed blowback 5.56? I think 10mm is already pushing the limits of the RDB system considering that it comes from the factory with the heaviest CMMG tuning weight installed in the carrier and I'm skeptical how much bigger they can make the angles on the bolt before it just won't rotate and then shear off like what I think would happen in 556. Also, my 'Ultimax' setup in 556 is an absolute dream to shoot suppressed and un-suppressed. I don't know what else I could do to make it better. |
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Originally Posted By amphibian: I know you must be joking but seriously that would be a bad idea. I think 10mm is already pushing the limits of the RDB system considering that it comes from the factory with the heaviest CMMG tuning weight installed in the carrier and I'm skeptical how much bigger they can make the angles on the bolt before it just won't rotate and then shear off like what I think would happen in 556. Also, my 'Ultimax' setup in 556 is an absolute dream to shoot suppressed and un-suppressed. I don't know what else I could do to make it better. Originally Posted By amphibian: Originally Posted By backbencher: Ready to try a rotary delayed blowback 5.56? I know you must be joking but seriously that would be a bad idea. I think 10mm is already pushing the limits of the RDB system considering that it comes from the factory with the heaviest CMMG tuning weight installed in the carrier and I'm skeptical how much bigger they can make the angles on the bolt before it just won't rotate and then shear off like what I think would happen in 556. Also, my 'Ultimax' setup in 556 is an absolute dream to shoot suppressed and un-suppressed. I don't know what else I could do to make it better. Mill your own carrier. I do think radial delayed blowback would suffice for subsonic .300 Blackout, but all bets would be off with a Super in there. |
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I'll preface this with the disclaimer that I have minimal familiarity with the RDB system, and only have one example currently. My hypothesis about the ejector spring life is a combination of two things: 1. Amphibian's observation about the case slamming rearward upon ignition. 2. The short 9mm case pivoting to the right inside the barrel extension then being forced back to nearly straight as the BCG continues rearward. The idea being the ejector spring could be getting battered twice with each cycle. I have not researched to see if 2 is valid or not, just a hunch. SIG ARs used to have an insert in the extension void inline with the extractor while in battery. Not sure if something similar is feasible, but inline with the extractor while "unlocked", to limit my hypothetical case pivot action. If anyone is smart enough to validate or invalidate this idea it's @amphibian. ETA: I got curious and dug my Guard SBR out. Dropped an empty case in the chamber, and closed the action. Upon slowly opening it, the observed casing angle is small, not as much as I imagined. Repeated this several times. Another observation: Ejector pressure felt decent, but the case stayed held by the extractor. Might have to play with springs for both. Final observation: I should probably clean and lube this thing if I expect it to have a chance at working.
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Originally Posted By badkarmaiii: I'll preface this with the disclaimer that I have minimal familiarity with the RDB system, and only have one example currently. My hypothesis about the ejector spring life is a combination of two things: 1. Amphibian's observation about the case slamming rearward upon ignition. 2. The short 9mm case pivoting to the right inside the barrel extension then being forced back to nearly straight as the BCG continues rearward. The idea being the ejector spring could be getting battered twice with each cycle. I have not researched to see if 2 is valid or not, just a hunch. SIG ARs used to have an insert in the extension void inline with the extractor while in battery. Not sure if something similar is feasible, but inline with the extractor while "unlocked", to limit my hypothetical case pivot action. If anyone is smart enough to validate or invalidate this idea it's @amphibian. I have moved on to getting these configurations working with Glock, Endomags, Colt mags and now Scorpion mags which require more work. |
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Wow, tons of great info here. I purchased my 9mm banshee around March this year and am having failure to eject issues after maybe 200-300 rounds. I can use a pick and push down the ejection pic down without much force. However, when comparing it to the force needed on any of my other ar’s (556/223), the force needed to push the ejection spring down feels very similar. So I’m not completely convinced that the ejection spring or pin is the issue. I also am trying to compare the ejection process on the banshee to my ar’s, not sure if that’s a smart way to do it since they are two different animals. But, that’s what I have to go off for now. So, in doing so I do notice that I can cycle unified rounds through my ar15’s by pulling the charging handle back and watching the bolt fling the round out of the ejection port. I assume the ar9 is no different since the bolt acts the same as far as the ejection process. I made this video today: https://youtube.com/shorts/mHIZL3F8rFc?si=O_FSYSTsJHI_yXEN You can see that the extractor grabs the round but the bolt just holds it. Also, the round isn’t flat on the bolt, it’s sitting on the bolt at an angle so the pin isn’t able to throw the round off the bolt. A couple things come to mind: 1) maybe the extractor spring is weak and not allowing the extractor to hold the case firmly when the bolt/bcg moves back? 2) maybe the extractor itself is worn/damaged and not holding the case firmly in the bolt when the bolt/bcg moves back? |
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Originally Posted By svdude: Wow, tons of great info here. I purchased my 9mm banshee around March this year and am having failure to eject issues after maybe 200-300 rounds. I can use a pick and push down the ejection pic down without much force. However, when comparing it to the force needed on any of my other ar’s (556/223), the force needed to push the ejection spring down feels very similar. So I’m not completely convinced that the ejection spring or pin is the issue. I also am trying to compare the ejection process on the banshee to my ar’s, not sure if that’s a smart way to do it since they are two different animals. But, that’s what I have to go off for now. So, in doing so I do notice that I can cycle unified rounds through my ar15’s by pulling the charging handle back and watching the bolt fling the round out of the ejection port. I assume the ar9 is no different since the bolt acts the same as far as the ejection process. I made this video today: https://youtube.com/shorts/mHIZL3F8rFc?si=O_FSYSTsJHI_yXEN You can see that the extractor grabs the round but the bolt just holds it. Also, the round isn’t flat on the bolt, it’s sitting on the bolt at an angle so the pin isn’t able to throw the round off the bolt. A couple things come to mind: 1) maybe the extractor spring is weak and not allowing the extractor to hold the case firmly when the bolt/bcg moves back? 2) maybe the extractor itself is worn/damaged and not holding the case firmly in the bolt when the bolt/bcg moves back?  Failed To Load Title |
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Originally Posted By svdude: Wow, tons of great info here. I purchased my 9mm banshee around March this year and am having failure to eject issues after maybe 200-300 rounds. I can use a pick and push down the ejection pic down without much force. However, when comparing it to the force needed on any of my other ar's (556/223), the force needed to push the ejection spring down feels very similar. So I'm not completely convinced that the ejection spring or pin is the issue. I also am trying to compare the ejection process on the banshee to my ar's, not sure if that's a smart way to do it since they are two different animals. But, that's what I have to go off for now. So, in doing so I do notice that I can cycle unified rounds through my ar15's by pulling the charging handle back and watching the bolt fling the round out of the ejection port. I assume the ar9 is no different since the bolt acts the same as far as the ejection process. I made this video today: https://youtube.com/shorts/mHIZL3F8rFc?si=O_FSYSTsJHI_yXEN You can see that the extractor grabs the round but the bolt just holds it. Also, the round isn't flat on the bolt, it's sitting on the bolt at an angle so the pin isn't able to throw the round off the bolt. A couple things come to mind: 1) maybe the extractor spring is weak and not allowing the extractor to hold the case firmly when the bolt/bcg moves back? 2) maybe the extractor itself is worn/damaged and not holding the case firmly in the bolt when the bolt/bcg moves back? Now back to your point of the extractor not holding onto the case with enough tension for the ejector pin doing it's job is possible but as I've posted many times, I run almost exclusively suppressed and the CMMG RDB system appears to extract without an extractor even installed in the bolt with a suppressor mounted as seen in my video:  CMMG RDB Excessive Headspace Some have posted getting the BCM extractor kit. Some say it resolved their issues and some say it didn't. Either way, I think it is just a band aid. I think you need to measure the strength of your ejector spring as I mentioned on my site. https://c3junkie.com/?page_id=221 I have also updated my webpage above w/ 10 points at the top for people that don't want to read the whole thing. |
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Originally Posted By amphibian: The title of you video says failure to 'extract' but in the video, it is extracting the case from the chamber fine. Your issue is ejection not extraction. Now back to your point of the extractor not holding onto the case with enough tension for the ejector pin doing it's job is possible but as I've posted many times, I run almost exclusively suppressed and the CMMG RDB system appears to extract without an extractor even installed in the bolt with a suppressor mounted as seen in my video: https://www.youtube.com/watch?v=Y0DXCouLsIwSome have posted getting the BCM extractor kit. Some say it resolved their issues and some say it didn't. Either way, I think it is just a band aid. I think you need to measure the strength of your ejector spring as I mentioned on my site. https://c3junkie.com/?page_id=221 I have also updated my webpage above w/ 10 points at the top for people that don't want to read the whole thing. Given the CMMG is a delayed blowback system, hardly surprising it extracts w/o the extractor - if it didn't, it wouldn't be a semi-auto. |
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Originally Posted By backbencher: Given the CMMG is a delayed blowback system, hardly surprising it extracts w/o the extractor - if it didn't, it wouldn't be a semi-auto. Originally Posted By backbencher: Originally Posted By amphibian: The title of you video says failure to 'extract' but in the video, it is extracting the case from the chamber fine. Your issue is ejection not extraction. Now back to your point of the extractor not holding onto the case with enough tension for the ejector pin doing it's job is possible but as I've posted many times, I run almost exclusively suppressed and the CMMG RDB system appears to extract without an extractor even installed in the bolt with a suppressor mounted as seen in my video: https://www.youtube.com/watch?v=Y0DXCouLsIwSome have posted getting the BCM extractor kit. Some say it resolved their issues and some say it didn't. Either way, I think it is just a band aid. I think you need to measure the strength of your ejector spring as I mentioned on my site. https://c3junkie.com/?page_id=221 I have also updated my webpage above w/ 10 points at the top for people that don't want to read the whole thing. Given the CMMG is a delayed blowback system, hardly surprising it extracts w/o the extractor - if it didn't, it wouldn't be a semi-auto. |
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Originally Posted By svdude: Wow, tons of great info here. I purchased my 9mm banshee around March this year and am having failure to eject issues after maybe 200-300 rounds. I can use a pick and push down the ejection pic down without much force. However, when comparing it to the force needed on any of my other ar’s (556/223), the force needed to push the ejection spring down feels very similar. So I’m not completely convinced that the ejection spring or pin is the issue. I also am trying to compare the ejection process on the banshee to my ar’s, not sure if that’s a smart way to do it since they are two different animals. But, that’s what I have to go off for now. So, in doing so I do notice that I can cycle unified rounds through my ar15’s by pulling the charging handle back and watching the bolt fling the round out of the ejection port. I assume the ar9 is no different since the bolt acts the same as far as the ejection process. I made this video today: https://youtube.com/shorts/mHIZL3F8rFc?si=O_FSYSTsJHI_yXEN You can see that the extractor grabs the round but the bolt just holds it. Also, the round isn’t flat on the bolt, it’s sitting on the bolt at an angle so the pin isn’t able to throw the round off the bolt. A couple things come to mind: 1) maybe the extractor spring is weak and not allowing the extractor to hold the case firmly when the bolt/bcg moves back? 2) maybe the extractor itself is worn/damaged and not holding the case firmly in the bolt when the bolt/bcg moves back? The rim diameter of 9mm and .223 are not the same. I’ve had your exact problem with regular blowback ARs with M16 extractors when using subsonic ammo because the extractor was holding the brass too hard. Colt bolts do not use M16 extractors, though they certainly could have. They instead chose to design a new, narrower extractor for 9mm. My solution with blowback guns was to round the edge on the outer thirds of the M16’s extractor claw so that it only grips the rim with the center third of the claw. This has been successful in solving the issue with 4 blowback uppers that shared 2 bolts. My Colt-style bolt that came with a narrow extractor never had problems in any of these guns. I’d be willing to send you a modified extractor for free to see if it helps on a RDB setup also. |
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Originally Posted By amphibian: Did you look at my video showing that it only extracts w/o the extractor when suppressed with a 'good' barrel? Remove the suppressor and it doesn't extract. With a 'bad' barrel it will extract w/o the suppressor. The 'bad' barrel will kill ejector springs extremely fast. Originally Posted By amphibian: Originally Posted By backbencher: Originally Posted By amphibian: The title of you video says failure to 'extract' but in the video, it is extracting the case from the chamber fine. Your issue is ejection not extraction. Now back to your point of the extractor not holding onto the case with enough tension for the ejector pin doing it's job is possible but as I've posted many times, I run almost exclusively suppressed and the CMMG RDB system appears to extract without an extractor even installed in the bolt with a suppressor mounted as seen in my video: https://www.youtube.com/watch?v=Y0DXCouLsIwSome have posted getting the BCM extractor kit. Some say it resolved their issues and some say it didn't. Either way, I think it is just a band aid. I think you need to measure the strength of your ejector spring as I mentioned on my site. https://c3junkie.com/?page_id=221 I have also updated my webpage above w/ 10 points at the top for people that don't want to read the whole thing. Given the CMMG is a delayed blowback system, hardly surprising it extracts w/o the extractor - if it didn't, it wouldn't be a semi-auto. Did you look at my video showing that it only extracts w/o the extractor when suppressed with a 'good' barrel? Remove the suppressor and it doesn't extract. With a 'bad' barrel it will extract w/o the suppressor. The 'bad' barrel will kill ejector springs extremely fast. I did. In the CMMG system, what starts bolt movement? |
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Originally Posted By 1168RGR: Yeah, the extractor has a very different job in a (delayed) blowback 9mm than a 5.56 gun, given that the cartridge case is the gas piston. How is the job different? When the cartridge fires, the bolt will still rotate within the bcg. The difference is that in a 556, the bolt will rotate and move back at the same time where in the rdb setup, the bolt will rotate and draw the bcg forward till the chamfered lugs on the bolt clear the lugs on the barrel. The extractor still does the same job. The only difference I can imagine are possibly the forces acting on the extractor since with the rdb system, the extractor may play a part in holding the round while the bolt rotates and the friction of the cartridge in the chamber may put some extra stress on the extractor. I’m just speculating here because I don’t know if the cartridge rotates with the bolt or the bolt rotates around the cartridge. The 556 is similar except the cartridge moves away from the chamber as the bolt rotates and moves back. |
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Originally Posted By svdude: How is the job different? When the cartridge fires, the bolt will still rotate within the bcg. The difference is that in a 556, the bolt will rotate and move back at the same time where in the rdb setup, the bolt will rotate and draw the bcg forward till the chamfered lugs on the bolt clear the lugs on the barrel. The extractor still does the same job. The only difference I can imagine are possibly the forces acting on the extractor since with the rdb system, the extractor may play a part in holding the round while the bolt rotates and the friction of the cartridge in the chamber may put some extra stress on the extractor. I’m just speculating here because I don’t know if the cartridge rotates with the bolt or the bolt rotates around the cartridge. The 556 is similar except the cartridge moves away from the chamber as the bolt rotates and moves back. |
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Originally Posted By backbencher: Originally Posted By svdude: Wow, tons of great info here. I purchased my 9mm banshee around March this year and am having failure to eject issues after maybe 200-300 rounds. I can use a pick and push down the ejection pic down without much force. However, when comparing it to the force needed on any of my other ar's (556/223), the force needed to push the ejection spring down feels very similar. So I'm not completely convinced that the ejection spring or pin is the issue. I also am trying to compare the ejection process on the banshee to my ar's, not sure if that's a smart way to do it since they are two different animals. But, that's what I have to go off for now. So, in doing so I do notice that I can cycle unified rounds through my ar15's by pulling the charging handle back and watching the bolt fling the round out of the ejection port. I assume the ar9 is no different since the bolt acts the same as far as the ejection process. I made this video today: https://youtube.com/shorts/mHIZL3F8rFc?si=O_FSYSTsJHI_yXEN You can see that the extractor grabs the round but the bolt just holds it. Also, the round isn't flat on the bolt, it's sitting on the bolt at an angle so the pin isn't able to throw the round off the bolt. A couple things come to mind: 1) maybe the extractor spring is weak and not allowing the extractor to hold the case firmly when the bolt/bcg moves back? 2) maybe the extractor itself is worn/damaged and not holding the case firmly in the bolt when the bolt/bcg moves back? https://www.youtube.com/watch?v=mHIZL3F8rFc It really bugs me because I put so much work into this gun. |
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Originally Posted By svdude: How is the job different? When the cartridge fires, the bolt will still rotate within the bcg. The difference is that in a 556, the bolt will rotate and move back at the same time where in the rdb setup, the bolt will rotate and draw the bcg forward till the chamfered lugs on the bolt clear the lugs on the barrel. The extractor still does the same job. The only difference I can imagine are possibly the forces acting on the extractor since with the rdb system, the extractor may play a part in holding the round while the bolt rotates and the friction of the cartridge in the chamber may put some extra stress on the extractor. I’m just speculating here because I don’t know if the cartridge rotates with the bolt or the bolt rotates around the cartridge. The 556 is similar except the cartridge moves away from the chamber as the bolt rotates and moves back. Originally Posted By svdude: Originally Posted By 1168RGR: Yeah, the extractor has a very different job in a (delayed) blowback 9mm than a 5.56 gun, given that the cartridge case is the gas piston. How is the job different? When the cartridge fires, the bolt will still rotate within the bcg. The difference is that in a 556, the bolt will rotate and move back at the same time where in the rdb setup, the bolt will rotate and draw the bcg forward till the chamfered lugs on the bolt clear the lugs on the barrel. The extractor still does the same job. The only difference I can imagine are possibly the forces acting on the extractor since with the rdb system, the extractor may play a part in holding the round while the bolt rotates and the friction of the cartridge in the chamber may put some extra stress on the extractor. I’m just speculating here because I don’t know if the cartridge rotates with the bolt or the bolt rotates around the cartridge. The 556 is similar except the cartridge moves away from the chamber as the bolt rotates and moves back. Think about what operates a blowback gun. |
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| Well sure, the bcg moves rearward in a gas gun due to the redirection of gasses through a gas tube. But my point above is in regards to the stresses put on the extractor and how I think (could be wrong since I cannot test/prove the physics of it) the forces on it are extremely similar and that the extractor itself in a gas gun vs a blowback gun (ar specifically) has the same job. |
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Originally Posted By svdude: Well sure, the bcg moves rearward in a gas gun due to the redirection of gasses through a gas tube. But my point above is in regards to the stresses put on the extractor and how I think (could be wrong since I cannot test/prove the physics of it) the forces on it are extremely similar and that the extractor itself in a gas gun vs a blowback gun (ar specifically) has the same job. Quite a number of blowback guns will operate without an extractor present, as it is the case itself pushing the bolt open - the case is self extracting. In a delayed blowback gun, such as the CMMG, it's dependent on the residual gas pressure in the chamber & the tightness of the chamber. The repeated failures of the EJECTOR spring in the CMMG RDB seem to be related to the case compressing the spring flat on firing and the case continuing to keep pushing that spring flat as the case continues to push the bolt open, rather than being pulled by the ejector. Looks like a tight chamber such as Amphibians might mitigate that somewhat, but then add a can and you're back to square one. Hence the fixed ejector on CMMG's folow-on design. |
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Originally Posted By backbencher: The repeated failures of the EJECTOR spring in the CMMG RDB seem to be related to the case compressing the spring flat on firing and the case continuing to keep pushing that spring flat as the case continues to push the bolt open, rather than being pulled by the ejector. I’d tend to agree with you on the spring being compressed flat. But I don’t think that the headspace has anything to do with that. If the spring is being compressed flat, then it would seem to me that the issue is that the cavity that the spring and ejector pin sits in isn’t deep enough for the spring to compress properly. The ejector pin should be able to be pushed flush with the bolt cavity without the ejector spring being compressed flat. Regardless of headspace and the velocity at which the spring is compressed, that shouldn’t wear out a spring (at least not that much). I have some tubbs springs on the way. When they get here I’m going to measure the cavity that the spring and pin sits in and how much the tubs springs can compress to see if the spring is over compressed when the ejector pin is pushed flush with the bolt cavity. I’m betting that the math will tell me that the spring will be over compressed and in turn killing the spring. If this is the case then maybe the hole for the spring and ejector needs to be drilled another 1/32-1/16 deeper. Hopefully what I’ve written makes sense, I’ll try to have a more graphical illustration later on when I take my measurements. |
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Originally Posted By svdude: I’d tend to agree with you on the spring being compressed flat. But I don’t think that the headspace has anything to do with that. If the spring is being compressed flat, then it would seem to me that the issue is that the cavity that the spring and ejector pin sits in isn’t deep enough for the spring to compress properly. The ejector pin should be able to be pushed flush with the bolt cavity without the ejector spring being compressed flat. Regardless of headspace and the velocity at which the spring is compressed, that shouldn’t wear out a spring (at least not that much). I have some tubbs springs on the way. When they get here I’m going to measure the cavity that the spring and pin sits in and how much the tubs springs can compress to see if the spring is over compressed when the ejector pin is pushed flush with the bolt cavity. I’m betting that the math will tell me that the spring will be over compressed and in turn killing the spring. If this is the case then maybe the hole for the spring and ejector needs to be drilled another 1/32-1/16 deeper. Hopefully what I’ve written makes sense, I’ll try to have a more graphical illustration later on when I take my measurements. Originally Posted By svdude: Originally Posted By backbencher: The repeated failures of the EJECTOR spring in the CMMG RDB seem to be related to the case compressing the spring flat on firing and the case continuing to keep pushing that spring flat as the case continues to push the bolt open, rather than being pulled by the ejector. I’d tend to agree with you on the spring being compressed flat. But I don’t think that the headspace has anything to do with that. If the spring is being compressed flat, then it would seem to me that the issue is that the cavity that the spring and ejector pin sits in isn’t deep enough for the spring to compress properly. The ejector pin should be able to be pushed flush with the bolt cavity without the ejector spring being compressed flat. Regardless of headspace and the velocity at which the spring is compressed, that shouldn’t wear out a spring (at least not that much). I have some tubbs springs on the way. When they get here I’m going to measure the cavity that the spring and pin sits in and how much the tubs springs can compress to see if the spring is over compressed when the ejector pin is pushed flush with the bolt cavity. I’m betting that the math will tell me that the spring will be over compressed and in turn killing the spring. If this is the case then maybe the hole for the spring and ejector needs to be drilled another 1/32-1/16 deeper. Hopefully what I’ve written makes sense, I’ll try to have a more graphical illustration later on when I take my measurements. You might be on to something. How deep can that hole be drilled in the CMMG bolt? In hardened steel? |
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Originally Posted By backbencher: You might be on to something. How deep can that hole be drilled in the CMMG bolt? In hardened steel? I’m not sure. If it has to be drilled I’ll take my parts and suspicion to a good gunsmith and have them do the work. I don’t have the tooling to do that. |
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| The first question is, what is the hole depth compared to a 5.56 ejector hole? If the ejector and the spring are the same between both and the hole depth is the same then the spring shouldn't be compressing flat, or any flatter than it does with 5.56. Second question would be, would drilling deeper be of any benefit to the ejector function? |
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Originally Posted By SSTPAC: The first question is, what is the hole depth compared to a 5.56 ejector hole? If the ejector and the spring are the same between both and the hole depth is the same then the spring shouldn't be compressing flat, or any flatter than it does with 5.56. Second question would be, would drilling deeper be of any benefit to the ejector function? I plan on comparing the bolt measurements soon to see if there is a difference between the depths of the hole. One thing that I did notice when taking the spring and pin out of the bolt was that it was absolutely filthy. It may be possible that the carbon and other junk in there was taking up the valuable space and reducing the amount of room the spring has to compress and causing the spring to compress flat. I will admit, there’s definitely not much room to play with. I measured between 0.009-0.010” of space between the coils on the spring. So there’s not much room there for junk to go and still allow room for spring compression. Cmmg did however drill a hole at the end of the spring cavity so I’m assuming that they did this to allow an exit for some of the junk? |
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So, a few quick measurements. The depth of the spring/pin ejector hole to the end of the lugs on the bolt is around 1.28”. The length of the spring and pin combined is 1.32”. From the end of the bolt at the lugs to the surface where the back of the casing sits on the bolt is 0.14”. So from the spring/pin hole to the recess of the bolt where the casing sits is 1.14”. That means that the spring will need to compress 0.18” when the case is seated firmly on the bolt. Also from my measurements the spring is capable of compressing 0.216” when it is fully compressed flat. So it appears that there’s room for the ejector pin to be pushed all the way down before over compressing the spring. Also for kicks I took apart a bolt from a Springfield saint victor chambered in 556. All the dimensions were exactly the same. The hole depth, spring/pin length, and the depth of the bolt from the lugs to where the case sits in the recess on the bolt. There was one difference in the ejector spring though which was that the spring from the Springfield rifle has 26 coils where the Cmmg spring has 24. I didn’t measure how much the spring can compress in the Springfield though since I didn’t see how that data would be relevant. |
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Continuing from above (2000 char limit for new members) At this point I don’t think the ejection spring is being over compressed. I did compare (only by feel) the extractor spring. It feels like the extractor spring in the Springfield ar15 is much stiffer than the spring in the Cmmg ar9. The ejector spring also feels (by hand) to have the same weight. I don’t have a gauge to test that but by just pushing the ejection pin down, they both feel the same. It’s hardly a solid science there but it’s all I have at the moment. I know that amphibian has taken measurements of the spring weight for the ejector and has hypothesized that a weight below 10 pounds is where failures start to occur. What I don’t recall reading were measurements of spring weight when the spring was new and when the spring had a few hundred or a thousand rounds on it. I would be curious to know those numbers. Either way, when I get my new springs in the mail, I’ll replace the extraction spring first and see if I can get some consistent extraction and ejection. If I do then I’ll assume the issue is a weak extraction spring causing the extractor to not hold the fired case firmly enough for the ejection pin to get a good push to eject the round. I’m not saying amphibian is wrong about the headspace being the issue. I’m just saying that I’m not able to wrap my head around why/how that would cause this. |
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Originally Posted By svdude: So, a few quick measurements. The depth of the spring/pin ejector hole to the end of the lugs on the bolt is around 1.28”. The length of the spring and pin combined is 1.32”. From the end of the bolt at the lugs to the surface where the back of the casing sits on the bolt is 0.14”. So from the spring/pin hole to the recess of the bolt where the casing sits is 1.14”. That means that the spring will need to compress 0.18” when the case is seated firmly on the bolt. Also from my measurements the spring is capable of compressing 0.216” when it is fully compressed flat. So it appears that there’s room for the ejector pin to be pushed all the way down before over compressing the spring. Also for kicks I took apart a bolt from a Springfield saint victor chambered in 556. All the dimensions were exactly the same. The hole depth, spring/pin length, and the depth of the bolt from the lugs to where the case sits in the recess on the bolt. There was one difference in the ejector spring though which was that the spring from the Springfield rifle has 26 coils where the Cmmg spring has 24. I didn’t measure how much the spring can compress in the Springfield though since I didn’t see how that data would be relevant. So the most extra depth we might be able to get would be maybe .07"? As far as understanding the extraction and ejection issues, pretend for a moment this is a straight blowback action, there are no bolt lugs, and the bolt does not rotate. |
Joined:
Jul 2024
Posts:
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EE: 100% (7)
AZ, USA
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Originally Posted By backbencher: So the most extra depth we might be able to get would be maybe .07"? As far as understanding the extraction and ejection issues, pretend for a moment this is a straight blowback action, there are no bolt lugs, and the bolt does not rotate. What I’m saying is that the cavity for the spring and pin is 1.14”, and the total length of the spring and pin is 1.32”. So the spring will need to compress 0.18” and is able to compress 0.216 inches. So basically when the bolt is firmly holding a round, the spring is 0.036” from fully compressed. In short, I don’t believe the ejector spring is ever being compressed flat. I agree, I don’t think that this being a rdb pistol has anything to do with the ejection issue. |
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