Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
BCM
User Panel

Page AR-15 » Rimfire and Pistol Calibers
AR Sponsor: bravocompany
Page / 3
Link Posted: 9/8/2023 11:59:10 AM EST
[#1]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Mad-Machinist:  Not trying to be a smart ass.....but with an unlocked action headspace isn't really possible to check. Do not decieve yourself, at no time is an RDB action ever locked.  When I make RDB barrels I make then like a make DI barrels, with a locking bolt. It seems to work as I have done quite a few with out complaint.
View Quote


Can't you run Go/No-Go gauges in straight blowback pistols?  Never used one before, nor tried to check, but if the action has an OOB safety, shouldn't the NoGo gague & OOB safety prevent the hammer/striker from falling?
VP
Link Posted: 9/12/2023 7:36:43 PM EST
[#2]
Reached out to CMMG for an updated bolt. They said they would send one out. Fingers crossed it works better.
Link Posted: 9/23/2023 4:11:45 PM EST
[#3]
New bolt arrived. Time to start the shot counter and see how long it lasts.
Link Posted: 9/24/2023 11:57:11 PM EST
[Last Edit: chevrofreak] [#4]
My girlfriend and I shot 2 matches last weekend and both of our CMMG's crapped the bed. Neither rifle had over 300 rounds on their current ejector spring.   I broke down today and bought her a Dissent upper to see if it will be more reliable.
Link Posted: 9/25/2023 11:28:58 AM EST
[#5]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By chevrofreak:
My girlfriend and I shot 2 matches last weekend and both of our CMMG's crapped the bed. Neither rifle had over 300 rounds on their current ejector spring.   I broke down today and bought her a Dissent upper to see if it will be more reliable.
View Quote
That sucks...have you considered the JP-5?  
Link Posted: 9/25/2023 12:03:11 PM EST
[#6]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
That sucks...have you considered the JP-5?  
View Quote

I have, and I have 2 of them configured on the JP site and just haven't pulled the trigger.   I built a new PCC for competition use with the Maxim RDB buffer and it talked me out of spending the money on a JP.

Unfortunately both CMMG PCC's were being used by my girlfriend when they had repeated malfunctions.  We had a day match, followed by a night match and during the day match my girlfriend's rifle jammed so bad that she had to quit a stage and unfortunately got DQ'd when she AD'd the rifle during unload and show clear.  The spent, unejected case remained on the bolt face, and fed another cartridge into the chamber.  When she cleared the spent case, the gun would not chamber another round and she did not think to rack the bolt without a magazine inserted to ensure the chamber was clear, and when she dropped the hammer fired a round into the ground in front of the target array.   During the night match she ran my rifle with a suppressor and ended up having the same failure to extract problems that plagued her during the day match.   Needless to say, she was very frustrated.  We both have other PCC's, but our CMMG's are SBR's and that is what she prefers shooting in matches.
Link Posted: 9/25/2023 12:20:46 PM EST
[#7]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By chevrofreak:

I have, and I have 2 of them configured on the JP site and just haven't pulled the trigger.   I built a new PCC for competition use with the Maxim RDB buffer and it talked me out of spending the money on a JP.

Unfortunately both CMMG PCC's were being used by my girlfriend when they had repeated malfunctions.  We had a day match, followed by a night match and during the day match my girlfriend's rifle jammed so bad that she had to quit a stage and unfortunately got DQ'd when she AD'd the rifle during unload and show clear.  The spent, unejected case remained on the bolt face, and fed another cartridge into the chamber.  When she cleared the spent case, the gun would not chamber another round and she did not think to rack the bolt without a magazine inserted to ensure the chamber was clear, and when she dropped the hammer fired a round into the ground in front of the target array.   During the night match she ran my rifle with a suppressor and ended up having the same failure to extract problems that plagued her during the day match.   Needless to say, she was very frustrated.  We both have other PCC's, but our CMMG's are SBR's and that is what she prefers shooting in matches.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By chevrofreak:
Originally Posted By amphibian:
That sucks...have you considered the JP-5?  

I have, and I have 2 of them configured on the JP site and just haven't pulled the trigger.   I built a new PCC for competition use with the Maxim RDB buffer and it talked me out of spending the money on a JP.

Unfortunately both CMMG PCC's were being used by my girlfriend when they had repeated malfunctions.  We had a day match, followed by a night match and during the day match my girlfriend's rifle jammed so bad that she had to quit a stage and unfortunately got DQ'd when she AD'd the rifle during unload and show clear.  The spent, unejected case remained on the bolt face, and fed another cartridge into the chamber.  When she cleared the spent case, the gun would not chamber another round and she did not think to rack the bolt without a magazine inserted to ensure the chamber was clear, and when she dropped the hammer fired a round into the ground in front of the target array.   During the night match she ran my rifle with a suppressor and ended up having the same failure to extract problems that plagued her during the day match.   Needless to say, she was very frustrated.  We both have other PCC's, but our CMMG's are SBR's and that is what she prefers shooting in matches.
That sucks...As you may have seen me post before, I think the JP-5 looks awesome and I would buy one if it was full auto compatible but the ejector sits right where the sear needs to go and I confirmed with JP that it wouldn't work.  I am still testing the MEAN Arms which I have running pretty good now but still need to see how many rounds it will go before it too starts having extractor / ejector spring failures.

I don't think I've seen anyone post any feedback on the JP-5.  I don't think I've seen anyone post on the Dissent either.  (not including Youtube influencers, talking here on ar15.com).

Good luck with the Dissent and hope to you post some feedback on it.  Since it has a fixed ejector, I would assume you would be GTG.
Link Posted: 9/25/2023 12:27:06 PM EST
[#8]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
That sucks...As you may have seen me post before, I think the JP-5 looks awesome and I would buy one if it was full auto compatible but the ejector sits right where the sear needs to go and I confirmed with JP that it wouldn't work.  I am still testing the MEAN Arms which I have running pretty good now but still need to see how many rounds it will go before it too starts having extractor / ejector spring failures.

I don't think I've seen anyone post any feedback on the JP-5.  I don't think I've seen anyone post on the Dissent either.  (not including Youtube influencers, talking here on ar15.com).

Good luck with the Dissent and hope to you post some feedback on it.  Since it has a fixed ejector, I would assume you would be GTG.
View Quote


Since I had it sitting in my cart for a couple of days before ordering, CMMG emailed me a 10% off coupon. At $1305 shipped for a Sniper Grey 6.5" upper that will match her registered lower I couldn't pass it up.   I will try to post feedback about the reliability compared to the Banshee's.
Link Posted: 10/3/2023 5:42:58 PM EST
[#9]
Does anyone have a high round county 5.7 or 4.6 rdb? Did they have the spring issues? Did they use the same spring?
Link Posted: 10/4/2023 6:17:01 AM EST
[Last Edit: Joedirt199] [#10]
Lots of JP5 chatter over on the BrianEnos forum under their pistol caliber carbine section.
Link Posted: 10/16/2023 12:39:28 AM EST
[#11]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:

Good luck with the Dissent and hope to you post some feedback on it.  Since it has a fixed ejector, I would assume you would be GTG.
View Quote

We've had a chance to run the Dissent upper a bit, and so far so good.  The ejection is very positive, tossing cases at least 10ft even with some of my light loaded 135gr subsonic.   My girlfriend was doing fast, accurate double and triple taps that put a huge grin on her face.  She shot it back to back with her Banshee and she likes the Dissent so much more.  I don't know if the 6.5" barrel vs 8" barrel makes much difference l, but I agree with her that the Dissent is more fun to shoot.  It sounded awesome suppressed, too.

The down side is that you *have* to use their included end plate, which will prevent you from swapping uppers around unless whatever upper you put on uses a forward side charging handle.  I ended up ordering a Glock mag lower that we are going to SBR to alleviate the other problem she has, of not being able to easily seat the Endomag on a closed bolt, even when downloaded.
Link Posted: 10/30/2023 12:36:23 AM EST
[Last Edit: Alien] [#12]
My home built 9mm RDB gun ran a lot better with the heaviest weight and BCM extractor upgrade, but the failures still reared their head at the end of my session (which was surprising when it happened because it was fine before that). I swapped the ejector spring after my last outing where I had a few failures to extract. The factory spring was slightly shorter than the spares/replacements I ordered from CMMG a while back. I'm hoping that this solves the issue. I'll be taking her back out next weekend.

Edit: I finally got out to shoot. I only wound up shooting a couple of mags through it, but no malfunctions with the RDB with the new ejector spring, BCM extractor upgrade kit, and heaviest BCG weight. I might try and reduce the BCG weight to the lightest one and see how it performs next time since it might not be necessary if the ejector spring was the issue.


Link Posted: 11/11/2023 8:34:45 AM EST
[#13]
I bought a 9mm bolt and barrel kit this summer. My bolt is marked 50, so apparently it's the new bolt.  The gun ran fine for 200 rounds, all suppressed. Yesterday, the ejection issue reared its ugly head. I pulled the bolt and there's very little tension on the ejector. So no, the new bolt and MK10 spring did not solve the issues.!
Link Posted: 11/11/2023 9:45:10 PM EST
[#14]
What buffer weight and bcg weight is everyone running? Is the ejection issue potentially related to bolt speed? CMMG recommends a H1 buffer I have heard, but I personally haven't seen this literature.  In the RDB manual pdf I have it only references buffer weight with the MK10 10mm platform. In the 9mm AR platforms in general we use reciprocating mass to reduce recoil, but can this have the negative side effect of reducing ejection reliability aswell? Does having a lower reciprocating mass/higher bolt speed make the system more "punchy" but increase ejection reliability?
Link Posted: 11/12/2023 9:35:10 AM EST
[#15]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By SSTPAC:
What buffer weight and bcg weight is everyone running? Is the ejection issue potentially related to bolt speed? CMMG recommends a H1 buffer I have heard, but I personally haven't seen this literature.  In the RDB manual pdf I have it only references buffer weight with the MK10 10mm platform. In the 9mm AR platforms in general we use reciprocating mass to reduce recoil, but can this have the negative side effect of reducing ejection reliability aswell? Does having a lower reciprocating mass/higher bolt speed make the system more "punchy" but increase ejection reliability?
View Quote


I'm using a H2 buffer. It ejects about 4:30. An H1 would probably be better, as it wont lock back on empty using subs and a H2 buffer. I put a new 5.56 ejector spring in it yesterday and fired 60 rounds without issue. Based on my experiences, Id say bolt speed is not the issue.
Link Posted: 11/12/2023 2:17:58 PM EST
[#16]
I ordered mine in June of 2019 and haven't had to replace anything as of yet. Knock on wood... I shoot a couple hundred rounds once a month or so when my wife and I go to our local range. I do use Amphibian's 300blk flatwire and RB5007 buffer upgrades though. It's a 5" barrel SBR and is only shot suppressed. I guess I have something to look forward to...
Link Posted: 11/13/2023 6:11:34 PM EST
[#17]
Link Posted: 11/13/2023 8:24:48 PM EST
[#18]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Mad-Machinist:  I don't see how the problem can ever be eliminated with the ejector spring......short of a redisign with a fixed ejector. Having the ejector push the rim to front of the extractor groove and then having it slam against the bolt face when fired compressing the spring in milliseconds is probably exceeding the capability of the spring. Perhaps an extractor with a thinner groove that holds the case closer to the bolt face would help, but that has the drawback of possibly inpacting reliable feeding and the ability of the case to roll off/out of the extractor groove on ejection.
View Quote


That's exactly what they went to when they did their ARish bufferless design.
Link Posted: 11/14/2023 5:48:19 AM EST
[#19]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Mad-Machinist:
I don't see how the problem can ever be eliminated with the ejector spring......short of a redisign with a fixed ejector. Having the ejector push the rim to front of the extractor groove and then having it slam against the bolt face when fired compressing the spring in milliseconds is probably exceeding the capability of the spring. Perhaps an extractor with a thinner groove that holds the case closer to the bolt face would help, but that has the drawback of possibly inpacting reliable feeding and the ability of the case to roll off/out of the extractor groove on ejection.
View Quote


What effect would too stiff an extractor spring have on the ejector spring, if any. In my.gun, which wore out the ejector spring around 200 rounds, it is very difficult to move the extractor at all. There is considerably more wear on the extractor face than one would expect from such a low round count.
Link Posted: 11/14/2023 3:02:32 PM EST
[#20]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By molar:


What effect would too stiff an extractor spring have on the ejector spring, if any. In my.gun, which wore out the ejector spring around 200 rounds, it is very difficult to move the extractor at all. There is considerably more wear on the extractor face than one would expect from such a low round count.
View Quote
If you look at page 1 of this thread and the second video I posted, I prove that if you completely remove the extractor from the bolt of a suppressed CMMG RDB it will extract on it's own.  In fact, I ran a match of around 500 rounds where the extractor pin was broken and the extractor was just flopping around in there and it never missed a beat.  Didn't even know till I went home to clean it and the pieces fell out.
If you remove the suppressor, it will not extract though.  I guess some could also argue on the type of suppressor, ammo etc...whatever...I'm just saying in my configuration this is what happens.  My point is that not much extraction force is needed when suppressed which is 99% of my shooting.
Link Posted: 11/14/2023 3:44:33 PM EST
[#21]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:


If you look at page 1 of this thread and the second video I posted, I prove that if you completely remove the extractor from the bolt of a suppressed CMMG RDB it will extract on it's own.  In fact, I ran a match of around 500 rounds where the extractor pin was broken and the extractor was just flopping around in there and it never missed a beat.  Didn't even know till I went home to clean it and the pieces fell out.
If you remove the suppressor, it will not extract though.  I guess some could also argue on the type of suppressor, ammo etc...whatever...I'm just saying in my configuration this is what happens.  My point is that not much extraction force is needed when suppressed which is 99% of my shooting.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
Originally Posted By molar:  What effect would too stiff an extractor spring have on the ejector spring, if any. In my.gun, which wore out the ejector spring around 200 rounds, it is very difficult to move the extractor at all. There is considerably more wear on the extractor face than one would expect from such a low round count.


If you look at page 1 of this thread and the second video I posted, I prove that if you completely remove the extractor from the bolt of a suppressed CMMG RDB it will extract on it's own.  In fact, I ran a match of around 500 rounds where the extractor pin was broken and the extractor was just flopping around in there and it never missed a beat.  Didn't even know till I went home to clean it and the pieces fell out.
If you remove the suppressor, it will not extract though.  I guess some could also argue on the type of suppressor, ammo etc...whatever...I'm just saying in my configuration this is what happens.  My point is that not much extraction force is needed when suppressed which is 99% of my shooting.


Given the action depends on the cartridge pushing the bolt to work, that it would run w/o an extractor isn't very surprising.
Link Posted: 11/15/2023 7:29:24 PM EST
[#22]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
If you look at page 1 of this thread and the second video I posted, I prove that if you completely remove the extractor from the bolt of a suppressed CMMG RDB it will extract on it's own.  In fact, I ran a match of around 500 rounds where the extractor pin was broken and the extractor was just flopping around in there and it never missed a beat.  Didn't even know till I went home to clean it and the pieces fell out.
If you remove the suppressor, it will not extract though.  I guess some could also argue on the type of suppressor, ammo etc...whatever...I'm just saying in my configuration this is what happens.  My point is that not much extraction force is needed when suppressed which is 99% of my shooting.
View Quote


It seems like the more tension on the extractor, the stiffer the ejector spring needs to be to overcome.  Would that be safe to assume?
Link Posted: 11/15/2023 9:33:15 PM EST
[Last Edit: amphibian] [#23]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By molar:


It seems like the more tension on the extractor, the stiffer the ejector spring needs to be to overcome.  Would that be safe to assume?
View Quote
I don't think it really matters in regards to the ejector spring life.   Again, video I posted on page 1 pasted below.
Dummy round in chamber.
Imagine when the round is detonated and you have this much slop between the lugs of the bolt and barrel extension.  
Like hitting a brick wall, that is what is killing the ejector springs.  
Do this same test with an MP5 and this doesn't happen there is no slop.  I tested my new MEAN Arms bearing delay and it doesn't do this either.


Again, I had a custom barrel made with no slop but then it isn't violent enough to work with the spring loaded ejector and now you must have a custom fixed ejector like I did.
Link Posted: 11/15/2023 10:32:42 PM EST
[#24]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
I don't think it really matters in regards to the ejector spring life.   Again, video I posted on page 1 pasted below.
Dummy round in chamber.
Imagine when the round is detonated and you have this much slop between the lugs of the bolt and barrel extension.  
Like hitting a brick wall, that is what is killing the ejector springs.  
Do this same test with an MP5 and this doesn't happen there is no slop.  I tested my new MEAN Arms bearing delay and it doesn't do this either.
https://www.youtube.com/watch?v=xhm4omLtW2s

Again, I had a custom barrel made with no slop but then it isn't violent enough to work with the spring loaded ejector and now you must have a custom fixed ejector like I did.
View Quote


Interesting. My recent manufacture barrel and bolt doesnt have much slop at all it seems, but the ejector spring still wore out after a couple hundred rounds
Link Posted: 11/21/2023 10:03:58 AM EST
[Last Edit: Gotterdammerung] [#25]
Mean Arms just announced "exomags" that will work with their Bearing Delay upper and the CMMG RDB. They will come in 10,15,20,32 and 40 round capacities.  

Exomags

Link Posted: 11/21/2023 11:06:34 AM EST
[#26]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Gotterdammerung:
Mean Arms just announced "exomags" that will work with their Bearing Delay upper and the CMMG RDB. They will come in 10,15,20,32 and 40 round capacities.  

Exomags

View Quote
Thanks!   I just pre ordered a 10 pack.  Hope they are reliable.
Link Posted: 11/21/2023 11:08:40 AM EST
[#27]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
Thanks!   I just pre ordered a 10 pack.  Hope they are reliable.
View Quote

I just ordered a 10 pack of the 40 rounders myself.  I hope they seat more easily on a closed bolt.
Link Posted: 11/23/2023 12:08:08 PM EST
[#28]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Mad-Machinist:
I don't see how the problem can ever be eliminated with the ejector spring......short of a redisign with a fixed ejector. Having the ejector push the rim to front of the extractor groove and then having it slam against the bolt face when fired compressing the spring in milliseconds is probably exceeding the capability of the spring. Perhaps an extractor with a thinner groove that holds the case closer to the bolt face would help, but that has the drawback of possibly inpacting reliable feeding and the ability of the case to roll off/out of the extractor groove on ejection.
View Quote


As far as I can tell (I've been following this for years) there is not a solution the RDB ejector problem except for a fixed ejector.  Is it possible that you can create a fixed ejector solution and offer it to RDB owners?  I feel this would be a viable product with a lot of orders.
Link Posted: 11/23/2023 1:37:03 PM EST
[#29]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BartCarter:


As far as I can tell (I've been following this for years) there is not a solution the RDB ejector problem except for a fixed ejector.  Is it possible that you can create a fixed ejector solution and offer it to RDB owners?  I feel this would be a viable product with a lot of orders.
View Quote

I would buy that.
Link Posted: 1/6/2024 7:34:38 PM EST
[#30]
I see no fixed ejector solution available yet.
Link Posted: 1/6/2024 8:12:32 PM EST
[#31]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BartCarter:


As far as I can tell (I've been following this for years) there is not a solution the RDB ejector problem except for a fixed ejector.  Is it possible that you can create a fixed ejector solution and offer it to RDB owners?  I feel this would be a viable product with a lot of orders.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BartCarter:
Originally Posted By Mad-Machinist:
I don't see how the problem can ever be eliminated with the ejector spring......short of a redisign with a fixed ejector. Having the ejector push the rim to front of the extractor groove and then having it slam against the bolt face when fired compressing the spring in milliseconds is probably exceeding the capability of the spring. Perhaps an extractor with a thinner groove that holds the case closer to the bolt face would help, but that has the drawback of possibly inpacting reliable feeding and the ability of the case to roll off/out of the extractor groove on ejection.


As far as I can tell (I've been following this for years) there is not a solution the RDB ejector problem except for a fixed ejector.  Is it possible that you can create a fixed ejector solution and offer it to RDB owners?  I feel this would be a viable product with a lot of orders.
I'm not @Mad-Machinist but as mentioned in other threads, I have a custom fixed ejector and I installed another one for a Colt 633 DoE build last week using the CMMG RDB system.

The bolt needs to be milled near the cam pin hole which creates a weak spot and mine eventually cracked..... it is a pain to deal with when a bolt breaks as the gun is all locked up.

I've had several people ask me to do the work for them but I won't do it since I know it will fail at some point and I don't want to support it.  It is also a bit of work to mill out the carrier as well and I don't want to deal with refinishing the parts after machining either.  

Bottom line, iMHO there is no money in doing it (time consuming and if hourly shop rates were used forget it..)  I suspect CMMG probably already knows this and didn't do the fixed ejector for this reason.  They did it on the Dissent since it uses a longer bolt and they were able to stay away from the cam pin hole.
Link Posted: 1/9/2024 10:35:51 AM EST
[#32]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
I'm not @Mad-Machinist but as mentioned in other threads, I have a custom fixed ejector and I installed another one for a Colt 633 DoE build last week using the CMMG RDB system.

The bolt needs to be milled near the cam pin hole which creates a weak spot and mine eventually cracked..... it is a pain to deal with when a bolt breaks as the gun is all locked up.

I've had several people ask me to do the work for them but I won't do it since I know it will fail at some point and I don't want to support it.  It is also a bit of work to mill out the carrier as well and I don't want to deal with refinishing the parts after machining either.  

Bottom line, iMHO there is no money in doing it (time consuming and if hourly shop rates were used forget it..)  I suspect CMMG probably already knows this and didn't do the fixed ejector for this reason.  They did it on the Dissent since it uses a longer bolt and they were able to stay away from the cam pin hole.
View Quote


Not to shift the topic, but have you found the MEAN bearing delayed upper to be a suitable alternative to the CMMG? I know you were working with that system for awhile but haven't seen much on it recently and don't see any write-ups on your site.
Link Posted: 1/9/2024 11:11:22 AM EST
[Last Edit: amphibian] [#33]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:


Not to shift the topic, but have you found the MEAN bearing delayed upper to be a suitable alternative to the CMMG? I know you were working with that system for awhile but haven't seen much on it recently and don't see any write-ups on your site.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:
Originally Posted By amphibian:
I'm not @Mad-Machinist but as mentioned in other threads, I have a custom fixed ejector and I installed another one for a Colt 633 DoE build last week using the CMMG RDB system.

The bolt needs to be milled near the cam pin hole which creates a weak spot and mine eventually cracked..... it is a pain to deal with when a bolt breaks as the gun is all locked up.

I've had several people ask me to do the work for them but I won't do it since I know it will fail at some point and I don't want to support it.  It is also a bit of work to mill out the carrier as well and I don't want to deal with refinishing the parts after machining either.  

Bottom line, iMHO there is no money in doing it (time consuming and if hourly shop rates were used forget it..)  I suspect CMMG probably already knows this and didn't do the fixed ejector for this reason.  They did it on the Dissent since it uses a longer bolt and they were able to stay away from the cam pin hole.


Not to shift the topic, but have you found the MEAN bearing delayed upper to be a suitable alternative to the CMMG? I know you were working with that system for awhile but haven't seen much on it recently and don't see any write-ups on your site.
Nope... I'm pretty discouraged with it after replacing the ejector spring and it basically dying in 300 rounds....worse than the CMMG....  Although I know I'm a special case as not many people are running suppressed and full auto...it may be fine for those not running suppressed and full auto.
I'm shelving both right now....although if I had to run a match right now with a closed bolt 9mm it would be the CMMG RDB w/ my fixed ejector...till the bolt breaks again but I'd estimate, I have approximately at least another 20K rounds before that happens again.


I'm working on something now that I have high hopes for...should have none of these ejector issues.
Link Posted: 1/9/2024 11:30:00 AM EST
[#34]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
Nope... I'm pretty discouraged with it after replacing the ejector spring and it basically dying in 300 rounds....worse than the CMMG....  Although I know I'm a special case as not many people are running suppressed and full auto...it may be fine for those not running suppressed and full auto.
I'm shelving both right now....although if I had to run a match right now with a closed bolt 9mm it would be the CMMG RDB w/ my fixed ejector...till the bolt breaks again but I'd estimate, I have approximately at least another 20K rounds before that happens again.


I'm working on something now that I have high hopes for...should have none of these ejector issues.
View Quote


Would it be possible to drill a second hole in the CMMG bolt and add a second ejector, similar to the DPMS G2 bolts?

Link Posted: 1/9/2024 11:38:47 AM EST
[Last Edit: amphibian] [#35]
Discussion ForumsJump to Quoted PostQuote History
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
View Quote
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.
Link Posted: 1/9/2024 11:53:39 AM EST
[#36]
Discussion ForumsJump to Quoted PostQuote History
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.
View Quote


Could something like a dual-ejector KAK bolt have the lugs milled at an angle to create a RDB bolt?

https://kakindustry.com/k-spec-enhanced-ar15-bolt-5-56-300-blackout-dual-ejector-c158-nitride/

Seems like if you had two ejectors that each settled to about 4lb, you'd have 8lbs total even after the springs shortened from their initial length.
Link Posted: 1/9/2024 12:03:55 PM EST
[#37]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:


Could something like a dual-ejector KAK bolt have the lugs milled at an angle to create a RDB bolt?

https://kakindustry.com/k-spec-enhanced-ar15-bolt-5-56-300-blackout-dual-ejector-c158-nitride/

Seems like if you had two ejectors that each settled to about 4lb, you'd have 8lbs total even after the springs shortened from their initial length.
View Quote
You go for it...I'm done....
Personally, I would rather run my fixed ejector than dual spring loaded ejectors.
Link Posted: 1/9/2024 12:20:08 PM EST
[#38]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
You go for it...I'm done....
Personally, I would rather run my fixed ejector than dual spring loaded ejectors.
View Quote


I wish I had the skills or equipment to do so . . .
Link Posted: 1/9/2024 12:22:58 PM EST
[#39]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:


I wish I had the skills or equipment to do so . . .
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:
Originally Posted By amphibian:
You go for it...I'm done....
Personally, I would rather run my fixed ejector than dual spring loaded ejectors.


I wish I had the skills or equipment to do so . . .
Are you running full auto?
Link Posted: 1/9/2024 1:00:10 PM EST
[#40]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
Are you running full auto?
View Quote


Yes on open-bolt platforms, but not on an AR/M16. However, I got the green light from my wife to buy another MG this year with the M16 being my current top choice, though I am discouraged by what I perceive as the lack of a trouble-free PCC option for it. I shoot almost exclusively suppressed these days and shoot many more pistol caliber rounds (mostly 9mm and .45) than rifle rounds, so that functionality is fairly key to my decision making.
Link Posted: 1/9/2024 1:12:17 PM EST
[#41]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:


Yes on open-bolt platforms, but not on an AR/M16. However, I got the green light from my wife to buy another MG this year with the M16 being my current top choice, though I am discouraged by what I perceive as the lack of a trouble-free PCC option for it. I shoot almost exclusively suppressed these days and shoot many more pistol caliber rounds (mostly 9mm and .45) than rifle rounds, so that functionality is fairly key to my decision making.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:
Originally Posted By amphibian:
Are you running full auto?


Yes on open-bolt platforms, but not on an AR/M16. However, I got the green light from my wife to buy another MG this year with the M16 being my current top choice, though I am discouraged by what I perceive as the lack of a trouble-free PCC option for it. I shoot almost exclusively suppressed these days and shoot many more pistol caliber rounds (mostly 9mm and .45) than rifle rounds, so that functionality is fairly key to my decision making.
Don't count out the AR/M16 yet...I'm waiting on parts to come in but if / when I have it working will post on the M16 forum of the Armory and probably UZItalk's M16 section.  May also post here in the Rimfire and Pistol section but it will really be focused on full auto users.
Link Posted: 1/9/2024 1:20:38 PM EST
[#42]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
Don't count out the AR/M16 yet...I'm waiting on parts to come in but if / when I have it working will post on the M16 forum of the Armory and probably UZItalk's M16 section.  May also post here in the Rimfire and Pistol section but it will really be focused on full auto users.
View Quote


That is great to hear. Maybe a premature question, but would it have any limitations in terms of RR, DIAS, or RLL? I've been leaning towards an RR.
Link Posted: 1/9/2024 1:46:40 PM EST
[#43]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:


That is great to hear. Maybe a premature question, but would it have any limitations in terms of RR, DIAS, or RLL? I've been leaning towards an RR.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By peachy:
Originally Posted By amphibian:
Don't count out the AR/M16 yet...I'm waiting on parts to come in but if / when I have it working will post on the M16 forum of the Armory and probably UZItalk's M16 section.  May also post here in the Rimfire and Pistol section but it will really be focused on full auto users.


That is great to hear. Maybe a premature question, but would it have any limitations in terms of RR, DIAS, or RLL? I've been leaning towards an RR.
I'm making it work for the RR and RDIAS but could easily do RLL as well.
Link Posted: 1/10/2024 2:29:56 PM EST
[#44]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:
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.
View Quote
Does anyone know why both Mean and CMMG abandoned the fixed ejector of the Colt Blowback design?


Link Posted: 1/10/2024 3:20:28 PM EST
[Last Edit: amphibian] [#45]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By dmk0210:
Does anyone know why both Mean and CMMG abandoned the fixed ejector of the Colt Blowback design?
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By dmk0210:
Originally Posted By amphibian:
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.
Does anyone know why both Mean and CMMG abandoned the fixed ejector of the Colt Blowback design?
Straight blowback is simple since it the bolt is one hunk of steel.... fixed ejector is a no-brainer there.

For the CMMG RDB, the bolt has to rotate so not so simple, not much metal at the bottom of the carrier...I also suspect CMMG may have also tried to do the fixed ejector initially with the RDB and maybe they had failed bolts like I did since you have to cut close to the cam pin hole (where my bolt broke on my fixed ejector setup).
Which is why they are now doing the Dissent RDB with a fixed ejector as they have elongated the bolt and kept it away from the cam pin hole.

If you want to read more about the custom fixed ejector for the CMMG: https://uzitalk.com/forums/index.php?threads/i-did-it-fixed-ejector-rdb.97420/

As mentioned in that thread, my buddy told me not to post any pictures but I spoke to him last week and he is OK with me doing it now so if there is enough interest I may do so but it looks a lot like what you seen in that thread but cleaner.

The prototype MEAN showed off at the 2020 Shot Show used some kind of cam mechanism for the ejector instead of relying on a spring that I was excited about but obviously didn't release that version.  I was told they had some reliability issues with that version (don't know if ejector related) which is why it wasn't released.
Link Posted: 1/10/2024 10:20:03 PM EST
[#46]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By amphibian:...Straight blowback is simple since it the bolt is one hunk of steel.... fixed ejector is a no-brainer there.

For the CMMG RDB, the bolt has to rotate so not so simple, not much metal at the bottom of the carrier...I also suspect CMMG may have also tried to do the fixed ejector initially with the RDB and maybe they had failed bolts like I did since you have to cut close to the cam pin hole (where my bolt broke on my fixed ejector setup).
Which is why they are now doing the Dissent RDB with a fixed ejector as they have elongated the bolt and kept it away from the cam pin hole.

If you want to read more about the custom fixed ejector for the CMMG: https://uzitalk.com/forums/index.php?threads/i-did-it-fixed-ejector-rdb.97420/

As mentioned in that thread, my buddy told me not to post any pictures but I spoke to him last week and he is OK with me doing it now so if there is enough interest I may do so but it looks a lot like what you seen in that thread but cleaner...
View Quote



I think people have been interested in this since you first mentioned it.  By all means, let's see the details.

Did this have any problems with cracks, etc.?  Does your buddy's fixed ejector get cut close to the cam pin hole?
Link Posted: 1/11/2024 5:19:21 AM EST
[#47]
Amphibian,
Do you think the machining for the ejector cut is just too close to the cam pin hole making the material too weak? Or is it the machining work hardens the bolt and makes a brittle spot/changes the heat treat making a weak spot?
Link Posted: 1/11/2024 7:01:53 AM EST
[#48]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BartCarter:


I think people have been interested in this since you first mentioned it.  By all means, let's see the details.

Did this have any problems with cracks, etc.?  Does your buddy's fixed ejector get cut close to the cam pin hole?
View Quote
My friend's setup is for his gas piston 9mm upper he made.   Since it is a piston the bolt is truly LOCKED there is no issue of stressing the bolt the same way the CMMG RDB does.  With the CMMG RDB, CMMG stated that there is more stress on the cam pin and it is supposedly made of stronger material to encounter this stress (BTW, I have broken two factory CMMG cam pins)
You can see a pic of the broken cam pin here:
CMMG RDB Excessive Headspace



He actually patented his setup and here is a link to his patent: https://patents.google.com/patent/US10690425B2/en?oq=10690425



Some of you may remember I was cutting my own angles on 5.45x39 bolts before CMMG came out with a .40SW bolt to further delay the action which is what I use now in my 9mm.

I also modified some bolts I got from my buddy that were for his 9mm piston but the bolts started to develop a crack near the cam pin hole...again due to the way the CMMG RDB works.  He has no issues with his bolts in a piston operating system.

Going with his bolt was nice since I didn't have to clearance it for the fixed ejector has his were made that way but again it started to develop a crack.

I will try to take some pics of mine and put on my web site for reference instead of posting multiple times the same thing.


Link Posted: 1/11/2024 7:03:40 AM EST
[#49]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By SSTPAC:
Amphibian,
Do you think the machining for the ejector cut is just too close to the cam pin hole making the material too weak? Or is it the machining work hardens the bolt and makes a brittle spot/changes the heat treat making a weak spot?
View Quote
It is the former, not leaving enough meat there for the CMMG RDB's method of operation which puts abuse on the cam pin.
Link Posted: 1/11/2024 7:13:51 AM EST
[Last Edit: amphibian] [#50]
I really think it is a lost cause at this point....however you do see some people say they have no problems and they supposedly shoot a lot too??

I guess myself and my local friends running full auto are just all unlucky.

That said, if I were NOT shooting full auto and wanted a delayed blowback setup to run on an AR pattern lower, why are you guys not looking at:

1.  The CMMG Dissent which uses the RDB action and a fixed ejector - available in 6.5" and 10.5" barrels
OR
2.  Angstadt Arms MDP-9 - they started selling just the upper Fall 2023 - uses an ejector mechanism like an MP5 where it moves in/out of the way of the bolt like a real MP5

I currently have no experience with either one at this time and I know both are expensive.
Both require you getting the entire upper not just a barrel and BCG like the original RDB

On the Dissent since it still uses the RDB system and I mentioned, I really wasn't that impressed with the out of the box recoil impulse until I went with a Kynshot RB5007 buffer, flat spring and a .40SW bolt, I'm skeptical I could get it to run as smooth as an MP5 or MP5K considering none of those options are available to be used with the Dissent....there is also the issue of possibly broken cam pins with the CMMG like I had (I broke them in stock form with no mods before I did the fixed ejector).

The MDP-9 has some bad reviews but they seem to be the early ones and may be resolved now
Page / 3
Page AR-15 » Rimfire and Pistol Calibers
AR Sponsor: bravocompany
Close Join Our Mail List to Stay Up To Date! Win a FREE Membership!

Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!

You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.


By signing up you agree to our User Agreement. *Must have a registered ARFCOM account to win.
Top Top