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Posted: 11/22/2019 7:03:41 PM EDT
[#1]
Quote HistoryQuoted:
I've got a Stern Defense 9mm mag block and an 8" CMMG Guard upper I assembled. With the upper mounted, the mag block will not insert all the way. With the upper removed, the mag block will insert properly. What do I need to modify so it all works properly? https://www.ar15.com/forums/armory/CMMG-Guard-with-Stern-defense-mag-block/23-494697/ https://www.ar15.com/forums/ar-15/CMMG-Banshee-9MM-Upper-and-Stern-Defense-Glock-Adapter/15-741698/ |
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Posted: 11/22/2019 9:04:34 PM EDT
[#2]
I was starting to have poor ejection with both my complete factory banshee and barrel/bolt banshee build on my registered sbr using endo mags. Sent an email to CMMG and they sent me two new ejector springs which were invoiced as MK10 springs.
So it looks like they are using the springs from the new 10mm banshee. Shot them both today and the ejection is definitely stronger than the original springs. Hopefully they last longer than the originals. |
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Posted: 11/23/2019 6:48:19 AM EDT
[#3]
Quote HistoryQuoted:
I've got a Stern Defense 9mm mag block and an 8" CMMG Guard upper I assembled. With the upper mounted, the mag block will not insert all the way. With the upper removed, the mag block will insert properly. What do I need to modify so it all works properly? |
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Posted: 11/23/2019 8:57:08 AM EDT
[#4]
Quote HistoryQuoted:
I was starting to have poor ejection with both my complete factory banshee and barrel/bolt banshee build on my registered sbr using endo mags. Sent an email to CMMG and they sent me two new ejector springs which were invoiced as MK10 springs. So it looks like they are using the springs from the new 10mm banshee. Shot them both today and the ejection is definitely stronger than the original springs. Hopefully they last longer than the originals.T I was experiencing the same ejection spring failure of around 1K rounds with the .40SW CMMG RDB as well and when they announced the 10mm, I was thinking to myself that the spring would die even faster in 10mm and was hoping that they did something to address the spring failures for the 10mm that would carry over to the other calibers. The latest replacement ejector springs I received from CMMG (I got mine on 10/19) were after the 10mm came out and I was told they were made from new material and have resolved the ejector spring issues. I was assured these were the latest but mine were not invoiced as MK10 springs like yours were. I haven't started using the replacements they sent me yet but when I do, I'll be sure to keep track of the round count. Thanks for the info! |
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Posted: 11/23/2019 10:10:54 AM EDT
[#5]
Quote HistoryQuoted:
Do you know how many rounds you went through before you started having ejection failures? Around 1K like me and others? I was experiencing the same ejection spring failure of around 1K rounds with the .40SW CMMG RDB as well and when they announced the 10mm, I was thinking to myself that the spring would die even faster in 10mm and was hoping that they did something to address the spring failures for the 10mm that would carry over to the other calibers. The latest replacement ejector springs I received from CMMG (I got mine on 10/19) were after the 10mm came out and I was told they were made from new material and have resolved the ejector spring issues. I was assured these were the latest but mine were not invoiced as MK10 springs like yours were. I haven't started using the replacements they sent me yet but when I do, I'll be sure to keep track of the round count. Thanks for the info! These new springs are stronger. Brass was launched more to the 3-4 oclock position and further away than the old 1 o'clock ejection and at my feet. |
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Posted: 11/23/2019 3:24:25 PM EDT
[#6]
Today's report on my 11" 9mm Guard using 9ARC mags and stock spring/buffer setup:
170 round match No malfunctions I am at 1,540 total rounds with 1 FTEject malfunction around the 1,300 round mark, which was last match. I'll give it the benefit of the doubt and say it was ammo related. For today's match I did clean the gun well. A few hundred rounds before the FTE I had only been lubing it and not cleaning between matches. Not that it matters, but just as a data point. |
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Posted: 11/23/2019 5:25:25 PM EDT
[#7]
Are any of you that are using the 9arc mags having trouble inserting/seating the mags on a closed bolt? I cannot get mine to seat. I'm using a complete CMMG factory RDB upper on my built out lower. I bought six of the 9arc adapters and put them in brand new Gen3 Pmags.
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Posted: 11/23/2019 5:58:11 PM EDT
[#8]
Quote HistoryQuoted:
Are any of you that are using the 9arc mags having trouble inserting/seating the mags on a closed bolt? I cannot get mine to seat. I'm using a complete CMMG factory RDB upper on my built out lower. I bought six of the 9arc adapters and put them in brand new Gen3 Pmags. |
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Posted: 11/23/2019 6:38:02 PM EDT
[#9]
Quote HistoryQuoted:
Make sure you have 30 rounds. The 30th round should end on the left when looking down range. 31 rounds will fit, but will not lock on a closed bolt. 30 rounds still require a nice little mag tap on a closed bolt, cause it's tight. Quote HistoryQuoted:
Quoted:
Are any of you that are using the 9arc mags having trouble inserting/seating the mags on a closed bolt? I cannot get mine to seat. I'm using a complete CMMG factory RDB upper on my built out lower. I bought six of the 9arc adapters and put them in brand new Gen3 Pmags. 
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Posted: 11/24/2019 3:40:06 PM EDT
[#10]
Quote HistoryQuoted:
I didn't read all 22 pages, so bare with me please I Have an NFA glock mag lower and the CMMG RDB 9mm barrel and bolt in a standard aero precision upper. Been shooting it successfully with a standard lower and endo mags. Was able to pick up the NFA glock lower and wanted to try it out, as I have many guns that take glock mags and wanted to see how much it would take to work. I removed the ejector and it seemed to work fine. Had it at the range today and it functioned except a couple hang ups in the last round. Feeding issue. Reading the link to the post above makes me think the mag is sitting a hair high. Anyone here do this with a NFA glock lower or is everyone doing rhe DDLS lowers. I think I had 2 ftfs in about 70 rounds. Pic of the jammed round. https://www.AR15.Com/media/mediaFiles/3591/20191023_141428_jpg-1135144.JPG I put an RDB aero upper on an NFA glock lower yesterday. I only had about an hour with it, shot maybe 50-60 rounds with no issues, 5 rounds per mags, so several mag changes. I did notice some wear to the mag followers from the bolt on the last rounds. Try putting a glock mag into the NFA lower by itself (no upper). You'll notice that it allows for over insertion of the mags when the blow back ejector has been removed, and it has a lot of slop. The mag catch is undersized, because the blow back ejector is designed to limit magazine travel. I took some measurements: 0.186" NFA mag catch height 0.278" Glock OEM Gen3 mag catch height 0.323" ETS mag catch opening on magazine A re-designed mag catch would solve the problem. Maybe add material to the mag catch and file/form to fit correctly at the right height. The hole in the lower for the mag catch would probably need enlarged. A bit of work. An easier solution might be to file down the blow back ejector, to use it as a mag insertion limit. As long as it can clear the bolt, it should be fine. I'll have to look into this some more. This could be related to your ftf's on last rounds, or maybe not. I just started looking into the NFA glock lower + guard upper. Edit: if there was any upward pressure on the mag, it would likely jam. |
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Posted: 11/24/2019 3:41:56 PM EDT
[#11]
Quote HistoryQuoted:
I’ve been having an issue with extraction. Using the guard upper and the endomags. I think I’ve narrowed it down to my bolt catching on the endomag feedlips. The bolt is hitting them, then slowing down enough to not fully grab onto the empty case to extract it from the chamber. I’m getting some decent wear on the two feedlips(I’m assuming that’s what to call them) they’re the two rails at the front of the insert, in front of the 9mm follower. Anyone else see this issue? Any known fix? It almost seems that the endomag insert is sitting to proud of the pmag. My gen 2 endomags have a couple scratches on the feed ramp inside, sides, but nothing major. One had a burr on the follower. Minor wear. |
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Posted: 11/24/2019 5:41:30 PM EDT
[#12]
Quote HistoryQuote HistoryQuoted:
IM sent 
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Posted: 11/24/2019 11:43:06 PM EDT
[#13]
Those of you that have setup your guard for an RLL, who did you have modify the carrier? Thanks.
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Posted: 11/24/2019 11:55:18 PM EDT
[#14]
Quote HistoryQuoted:
Thanks guys. After removing the bullet guide and ejector, and filing down the mag catch by ~.04", the Guard-based upper I built worked flawlessly on my M16. https://i.imgur.com/aw1oyECl.jpg |
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Posted: 11/25/2019 7:21:02 AM EDT
[#15]
Quote HistoryQuoted:
Thanks guys. After removing the bullet guide and ejector, and filing down the mag catch by ~.04", the Guard-based upper I built worked flawlessly on my M16. www.dropbox.com/s/5zrx0rchuk94185/NFA_glock_lower_guard_mod.png?dl=0 I filed down the blow back extractor until it cleared the bolt. Now it only serves as a magazine over travel stop. I also shifted the ejector left, by shimming the gap with 8 layers of soda can. Now the ejector lines up with the mag lip. I'm going to try it as is before modding anything else. If the mag needs lowered a bit, like the stern block, then both the top of the mag catch and bottom of the blow back extractor would need reduced an equal amount. |
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Posted: 11/25/2019 1:13:18 PM EDT
[#16]
I bought the bolt and barrel 9mm "kit". I made a mag adepter for a lower that uses Sten and with another adapter uses Uzi magazines. I managed to get that thing to run very reliably. I wanted to have a LRBHO so I put together a Colt style lower and it worked for about a hundred rounds. Then started getting the dreaded fail to eject. So I put the upper on my working Sten/Uzi lower and same thing. Fail to eject. Kinda of a bummer. The bolt/barrel "kit" has about a little over 600 rounds through it. It started out strong and kind of petered out. I'm in communication with CMMG so we'll see what they say. After reading everything here and i'm guessing it's the ejector spring.
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Posted: 11/25/2019 8:48:40 PM EDT
[#17]
Quote HistoryQuoted:
Basically what I did. I also keep a spare unmodified AR 15 mag catch in my parts box and just swap them out if I want to fire 556 with the appropriate upper and mags. Don't even have to mess with changing the buffer and spring since I use adjustable gas blocks on most of my uppers. Sort of like gunsmithing with Leggos. Quote HistoryQuoted:
Basically what I did. I also keep a spare unmodified AR 15 mag catch in my parts box and just swap them out if I want to fire 556 with the appropriate upper and mags. Don't even have to mess with changing the buffer and spring since I use adjustable gas blocks on most of my uppers. Sort of like gunsmithing with Leggos. Quoted:
I'm wondering if the NFA glock lower needs something similar, since they were both designed to work with blowback systems. The locking lugs gouge the mag followers when moving the bolt in both directions. Lowering the mag a bit would probably help with clearance. Was your bolt catching on the mag follower? |
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Posted: 11/27/2019 6:18:24 PM EDT
[#18]
Thanks for the info. Looks like NFA sells replacement mag catches and ejectors, so I'll go ahead and lower the mag for clearance.
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Posted: 11/28/2019 6:09:18 PM EDT
[#19]
Quote HistoryQuoted:
I haven't shot it in 5.56mm with the modified magazine catch yet, but I cycled a bunch of dummy rounds through a 5.56mm upper last night and it seemed to work OK. |
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Posted: 11/30/2019 8:40:18 PM EDT
[#20]
Sorry I've been a ghost lately. Having a kid sure cuts into your shooting time.
Quick update to my 16" 9mm build that was having a light strike every 100rnds roughly. Between 150rnds and 600rnds when I didn't clean it at all. First off I cleaned the gun extremely well and really scrubbed the chamber as light strikes may have been from the bolt not fully seating. Finally got out to another local USPSA match this morning. Did great but totally biffed one stage so that took me out of the runnings. Shot roughly 175-180 rounds of the same Fiocchi 9ap 115grn ive been shooting previously and that I had issue with. Brings my total round count up to almost 800 rounds. Had zero light strikes today. So maybe the gun was just too dirty after not cleaning it since the first 150rnds. Also as far as I could tell ejection was still really strong. |
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Posted: 12/1/2019 1:07:50 PM EDT
[#21]
Updating my situation......
Everything is running flawlessly finally. I don’t know if going back and doing the recommended endomag “break in” is what did it, but things are going great now. Setup Cmmg 8” barrel and bolt combo Endomags Vltor a5 buffer Tubb spring Kynshot hydraulic buffer Amphibians recommended setup. Colt m16 lower and also using the same timer as amphibian. Some slight differences in rpm though. The ammo choice will change rof, so I’m wondering what ammo you tested amphibian that resulted in 622 rpm. I had 3 types of ammo out yesterday; Wolf 115-680 rpm PPU 124-680 rpm Maxxtech brass 115-620 rpm I tested 6 round bursts unsupressed. |
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Posted: 12/1/2019 1:49:11 PM EDT
[#22]
Quote HistoryQuoted:
Updating my situation...... Everything is running flawlessly finally. I don't know if going back and doing the recommended endomag "break in" is what did it, but things are going great now. Setup Cmmg 8" barrel and bolt combo Endomags Vltor a5 buffer Tubb spring Kynshot hydraulic buffer Amphibians recommended setup. Colt m16 lower and also using the same timer as amphibian. Some slight differences in rpm though. The ammo choice will change rof, so I'm wondering what ammo you tested amphibian that resulted in 622 rpm. I had 3 types of ammo out yesterday; Wolf 115-680 rpm PPU 124-680 rpm Maxxtech brass 115-620 rpm I tested 6 round bursts unsupressed. I also always do 10 round dumps for cyclic rate. How well lubed the gun is will greatly affect the cyclic rate as well. |
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Posted: 12/1/2019 1:51:52 PM EDT
[#23]
Just an FYI, I've been doing some buffer testing in this thread: https://www.ar15.com/forums/ar-15/DPM-Recoil-Reduction-System-vs-Hydraulic-buffer-EDIT-Armament-LARB-Mod-2-and-3-added-to-the-test-/118-744494/?r=-1&page=3&anc=7995870#i7995870
It has expanded to include an accelerometer but we had some issues with it so it is still ongoing but figured you guys may want to see some of the videos I took at 1000FPS. 4 shots in semi were to be done for each configuration. Firing from the lead sled was to reduce the 'human factor' as much as possible. Here is what the 8" CMMG RDB setup looked like: 
Here is what it looked like with the CMMG recommended buffer/spring configuration, running 115 Gr blazer, it would function fine when shoulder fired but would jam in the lead sled, only 2 rounds fired in the video below. https://youtu.be/m3ujzgklg3w You can clearly see how much smoother my preferred setup is over the CMMG recommended configuration in the following videos. Here is a video of my preferred setup with a modified 5.45 bolt for suppressed usage only with my 147Gr reloads but I'm shooting 115 Gr Blazer unsuppressed here. What is interesting about this is that since it is for suppressed usage only, the BCG doesn't go back far enough to engage the BHO but functions 100% https://youtu.be/1MPXyvVAbDI Lastly here is what the same setup above with my fixed ejector, modified 5.45 bolt, my 147Gr reloads and suppressed. https://youtu.be/bNRIuQpminc |
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Posted: 12/1/2019 2:33:01 PM EDT
[#24]
Quote HistoryQuoted:
Just an FYI, I've been doing some buffer testing in this thread: https://www.ar15.com/forums/ar-15/DPM-Recoil-Reduction-System-vs-Hydraulic-buffer-EDIT-Armament-LARB-Mod-2-and-3-added-to-the-test-/118-744494/?r=-1&page=3&anc=7995870#i7995870 It has expanded to include an accelerometer but we had some issues with it so it is still ongoing but figured you guys may want to see some of the videos I took at 1000FPS. 4 shots in semi were to be done for each configuration. Firing from the lead sled was to reduce the 'human factor' as much as possible. Here is what the 8" CMMG RDB setup looked like: http://c3junkie.com/wp-content/uploads/2019/12/CMMG-RDB-1024x512.jpg Here is what it looked like with the CMMG recommended buffer/spring configuration, running 115 Gr blazer, it would function fine when shoulder fired but would jam in the lead sled, only 2 rounds fired in the video below. https://youtu.be/m3ujzgklg3w You can clearly see how much smoother my preferred setup is over the CMMG recommended configuration in the following videos. Here is a video of my preferred setup with a modified 5.45 bolt for suppressed usage only with my 147Gr reloads but I'm shooting 115 Gr Blazer unsuppressed here. What is interesting about this is that since it is for suppressed usage only, the BCG doesn't go back far enough to engage the BHO but functions 100% https://youtu.be/1MPXyvVAbDI Lastly here is what the same setup above with my fixed ejector, modified 5.45 bolt, my 147Gr reloads and suppressed. https://youtu.be/bNRIuQpminc Pretty cool videos. The last video shows that the cutout buffer tube makes an excellent gas to shooter's face deliver system :) |
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Posted: 12/1/2019 8:54:48 PM EDT
[#25]
Quote HistoryQuoted:...Here is what it looked like with the CMMG recommended buffer/spring configuration, running 115 Gr blazer, it would function fine when shoulder fired but would jam in the lead sled, only 2 rounds fired in the video below... |
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Posted: 12/1/2019 8:59:22 PM EDT
[#26]
Quote HistoryQuoted:
Any idea why the lead sled jammed and shoulder fired didn't? |
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Posted: 12/12/2019 11:45:55 PM EDT
[#27]
Aw hell. I wish I had not found my way here searching for a solution to my 9mm fail to eject.
I sent a pic of my malfunction to CMMG and they are sending me "a few" new ejector springs. Does the fact that they are sending me more than one spring indicate that the issue is not resolved yet? I don't know my round count. Don't think I'm at 1000 yet, but past 500 for sure. I bought the 8" barrel/bolt and matched it with a CMMG 9mm upper with the larger port. I'm using the CMMG "pmag" conversion magazines. ammo is 147 grain jhp reloads, suppressed using 3.6 grains bullseye which has run flawlessly in my regular (colt magazine) 9mm until it got so dirty I could no longer pull the charging handle back one time from all the funk. I know for a fact the first 300 rounds ran perfect through the rifle and I was very happy with how much more quiet, lightweight and soft shooting it was. I appreciate any suggestions. |
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Posted: 12/13/2019 1:21:09 AM EDT
[#28]
Quote HistoryQuoted:
Aw hell. I wish I had not found my way here searching for a solution to my 9mm fail to eject. I sent a pic of my malfunction to CMMG and they are sending me "a few" new ejector springs. Does the fact that they are sending me more than one spring indicate that the issue is not resolved yet? I don't know my round count. Don't think I'm at 1000 yet, but past 500 for sure. I bought the 8" barrel/bolt and matched it with a CMMG 9mm upper with the larger port. I'm using the CMMG "pmag" conversion magazines. ammo is 147 grain jhp reloads, suppressed using 3.6 grains bullseye which has run flawlessly in my regular (colt magazine) 9mm until it got so dirty I could no longer pull the charging handle back one time from all the funk. I know for a fact the first 300 rounds ran perfect through the rifle and I was very happy with how much more quiet, lightweight and soft shooting it was. I appreciate any suggestions. |
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Posted: 12/13/2019 8:00:58 AM EDT
[#29]
Quote HistoryQuoted:
If this doesn't work a fixed or maybe an Oly style ejector However, I still have a few other RDB setups using the spring loaded ejector setup that I don't want to modify in hopes CMMG finally fixes it. |
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Posted: 12/13/2019 10:28:30 AM EDT
[#30]
Quote HistoryQuoted:
It is a drastic step but it certainly does work. My fixed ejector equipped CMMG RDB is the one I grab the most and has the highest round count. BTW, my setup isn't like the Oly style at all. However, I still have a few other RDB setups using the spring loaded ejector setup that I don't want to modify in hopes CMMG finally fixes it. |
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Posted: 12/15/2019 1:15:05 AM EDT
[#31]
Round count report:
I have reached 2,123 rounds using my replacement ejector spring CMMG sent me some time ago. This upper probably has closer to or over 3,000 rounds combined, but I only really started logging proper round counts after CMMG sent me the replacement ejector spring, which I then switched to a carbine buffer and spring to go to CMMGs stock setup. I am using the 9ARC endo mags. 95% of this ammo diet has been my own reloads - 115gr FMJ, Titegroup 4.5gr, mixed FC brass cases, pushing around 1,320 FPS out of my 11" Guard barrel. On the 2,123 rounds: 1 FTEject around 1,300th round So all in all, the setup is going strong so far. The FTEject at 1,300 rounds is not enough data to conclude any issues with the ejector spring at this time, and could have very well been ammo related but I have no evidence to conclude that way. I will continue to round count this setup until it starts failing consistently. I'll probably come back and post around 2,500 or later depending on what happens. |
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Posted: 12/15/2019 7:13:07 AM EDT
[#32]
Quote HistoryQuoted:
Round count report: I have reached 2,123 rounds using my replacement ejector spring CMMG sent me some time ago. This upper probably has closer to or over 3,000 rounds combined, but I only really started logging proper round counts after CMMG sent me the replacement ejector spring, which I then switched to a carbine buffer and spring to go to CMMGs stock setup. I am using the 9ARC endo mags. 95% of this ammo diet has been my own reloads - 115gr FMJ, Titegroup 4.5gr, mixed FC brass cases, pushing around 1,320 FPS out of my 11" Guard barrel. On the 2,123 rounds: 1 FTEject around 1,300th round So all in all, the setup is going strong so far. The FTEject at 1,300 rounds is not enough data to conclude any issues with the ejector spring at this time, and could have very well been ammo related but I have no evidence to conclude that way. I will continue to round count this setup until it starts failing consistently. I'll probably come back and post around 2,500 or later depending on what happens. I don't think that is the 'latest' which is the one for the 10mm...description of, "10BA455; Spring, Ejector MK10" I got some replacement springs when the 10mm came out (I think that was in October?) and was told they were the same but mine were NOT invoiced like above....mine were invoiced as being the 45 version. So I don't know if they were invoiced wrong or what. Others have been posting about getting the MK10 with no issues from CMMG but I'm not getting a response from them...I'll wait a few more days and bug them again. Anyways due to the timing of when you got your replacement spring, you may not have the MK10 ejector spring in there either....Do you still have the invoice of the replacement? |
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Posted: 12/15/2019 3:11:28 PM EDT
[#33]
I installed the new ejector spring that CMMG had sent me. My invoice says, 10BA455-Spring, Ejector, Mk10. It is certainly more robust than the original. I really hopes this works.
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Posted: 12/15/2019 8:47:16 PM EDT
[#34]
Quote HistoryQuoted:
Thanks for the update. I looked back on page 20 of this thread of your old posts regarding the replacement ejector spring you got from CMMG back in August 2019. I don't think that is the 'latest' which is the one for the 10mm...description of, "10BA455; Spring, Ejector MK10" I got some replacement springs when the 10mm came out (I think that was in October?) and was told they were the same but mine were NOT invoiced like above....mine were invoiced as being the 45 version. So I don't know if they were invoiced wrong or what. Others have been posting about getting the MK10 with no issues from CMMG but I'm not getting a response from them...I'll wait a few more days and bug them again. Anyways due to the timing of when you got your replacement spring, you may not have the MK10 ejector spring in there either....Do you still have the invoice of the replacement? |
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Posted: 12/17/2019 9:38:46 PM EDT
[#35]
Will any standard ar handguard work on these, say a bcm mcmr?
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Posted: 12/18/2019 4:36:15 AM EDT
[#36]
Yep, any handguard will work...what barrel length are you looking at?
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Posted: 12/18/2019 9:06:42 PM EDT
[#37]
8 inch
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Posted: 12/18/2019 10:48:59 PM EDT
[#38]
This may be relevant to you: https://www.ar15.com/forums/AR-15/Recommended-handguard-for-8-guard-barrel-and-3-lug-tip/15-746004/
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Posted: 12/28/2019 8:48:18 PM EDT
[#39]
Follow up on my short chamber barrel issue:
CMMG came through. After some good comms back and forth with Bryan from CMMG, they sent me an RMA prepaid shipping label for the assembled upper. They requested I send them the entire upper. I disassembled the upper and only sent them the upper receiver with the barrel installed with barrel nut, bolt and CH. I used a milspec barrel nut, so no special wrench would be required to remove the barrel in case they wanted to work on it. It took them about a week or so to get back to me via email once they received it. Bryan confirmed that they reamed the chamber. He also sent me a video of test firing the fully assembled upper after they had reamed the chamber, which I thought was very nice of them. During the same time, I went ahead and asked for a couple of the new MK10 replacement ejector springs. I got it all in the mail today nicely packed. Hand written notes from their gunsmith were also in the box, mentioning that the chamber leads were tight, that he reamed it, and tasked the testers to manual eject different factory live rounds. Nice little level of detail there. In the box were two new ejector springs with no markings on the bag, and no invoice, so I have no idea if they are the MK10s. I obviously plunk tested the newly chamber-reamed barrel. All factory rounds I tried passed the plunk tests. I must have tried 6 or more different types of factory rounds, rounds that were failing before, all were passing now. However, my 115gr FMJ reloads sometimes would stick, they must be right at the edge. These 115gr FMJs bullet profile is more akin to .357 Sig bullets in which the ogive comes out almost in a straight wall and then tapers in fast. These same reloads plunk test fine out of my other two 9mm Guard barrels. So I will have to start sitting them a little deeper, and use this upper as my default bullet seating checker. All in all, I think CMMG's customer service came through and made it right. I haven't shot it yet, but ill reassemble the upper and test fire soon. |
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Posted: 12/29/2019 7:00:31 AM EDT
[#40]
Quote HistoryQuoted:
Follow up on my short chamber barrel issue: CMMG came through. After some good comms back and forth with Bryan from CMMG, they sent me an RMA prepaid shipping label for the assembled upper. They requested I send them the entire upper. I disassembled the upper and only sent them the upper receiver with the barrel installed with barrel nut, bolt and CH. I used a milspec barrel nut, so no special wrench would be required to remove the barrel in case they wanted to work on it. It took them about a week or so to get back to me via email once they received it. Bryan confirmed that they reamed the chamber. He also sent me a video of test firing the fully assembled upper after they had reamed the chamber, which I thought was very nice of them. During the same time, I went ahead and asked for a couple of the new MK10 replacement ejector springs. I got it all in the mail today nicely packed. Hand written notes from their gunsmith were also in the box, mentioning that the chamber leads were tight, that he reamed it, and tasked the testers to manual eject different factory live rounds. Nice little level of detail there. In the box were two new ejector springs with no markings on the bag, and no invoice, so I have no idea if they are the MK10s. I obviously plunk tested the newly chamber-reamed barrel. All factory rounds I tried passed the plunk tests. I must have tried 6 or more different types of factory rounds, rounds that were failing before, all were passing now. However, my 115gr FMJ reloads sometimes would stick, they must be right at the edge. These 115gr FMJs bullet profile is more akin to .357 Sig bullets in which the ogive comes out almost in a straight wall and then tapers in fast. These same reloads plunk test fine out of my other two 9mm Guard barrels. So I will have to start sitting them a little deeper, and use this upper as my default bullet seating checker. All in all, I think CMMG's customer service came through and made it right. I haven't shot it yet, but ill reassemble the upper and test fire soon. Can you take dummy round or a round with no primer/powder, chamber it then take a rod and push on the round and see if you can feel a gap between the back of the bolt lugs and the extension lugs? All 3 of my factory CMMG barrels have at least a mm or so of movement when I do this test. I had a custom SS barrel made with that headspace slop removed that functions fine but haven't fired enough rounds to know if it fixed the issue yet. Seeing how some people have this ejection spring problem and some don't, I wonder if those that do not have the problem have little or no headspace gap. |
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Posted: 12/30/2019 10:07:04 PM EDT
[#41]
Quote HistoryQuoted:
I had posted several times that both of my 9mm CMMG RDB barrels and my .40SW barrel appear to have excessive headspacing. I think the excessive headspacing maybe what is killing the ejector springs so fast. Ejector springs die right around 1K rounds with all 3 of those barrels. (I just received the new MK10 ejector springs and haven't run them yet to see if it really resolves the issue though). Can you take dummy round or a round with no primer/powder, chamber it then take a rod and push on the round and see if you can feel a gap between the back of the bolt lugs and the extension lugs? All 3 of my factory CMMG barrels have at least a mm or so of movement when I do this test. I had a custom SS barrel made with that headspace slop removed that functions fine but haven't fired enough rounds to know if it fixed the issue yet. Seeing how some people have this ejection spring problem and some don't, I wonder if those that do not have the problem have little or no headspace gap. |
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Posted: 1/11/2020 10:56:08 AM EDT
[#42]
Quote HistoryQuoted:
I installed the new ejector spring that CMMG had sent me. My invoice says, 10BA455-Spring, Ejector, Mk10. It is certainly more robust than the original. I really hopes this works. And managed to kill a really large hog with my 9 mm this week. I only have about three magazines down the tube with that new spring, but so far so good. |
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Posted: 1/11/2020 10:57:20 AM EDT
[#43]
sorry for the double post
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Posted: 1/11/2020 5:40:49 PM EDT
[#44]
@Amphibian, if you had to guess, how much did you lower your feed ramps? I'm running rounds straight into the ramp enough that the feed ramp edge digs into the lower half of the bullet locking it up. I lowered my mag release .06" at first and it worked enough to run 4 or 5 mags through with 3 failures using a standard upper. I switched to a Gibbz G4 and I could not chamber a round. Lowered the mag release .015" and now the rounds are hitting the feed ramp. This is a QC10 Colt lower, I'm worried if I lower the feed ramps it will become too thin. I will round and polish that edge 1st but wanted to see how much you removed and what you have left.
 Attached File |
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Posted: 1/11/2020 6:40:42 PM EDT
[#45]
Quote HistoryQuoted:
@Amphibian, if you had to guess, how much did you lower your feed ramps? I'm running rounds straight into the ramp enough that the feed ramp edge digs into the lower half of the bullet locking it up. I lowered my mag release .06" at first and it worked enough to run 4 or 5 mags through with 3 failures using a standard upper. I switched to a Gibbz G4 and I could not chamber a round. Lowered the mag release .015" and now the rounds are hitting the feed ramp. This is a QC10 Colt lower, I'm worried if I lower the feed ramps it will become too thin. I will round and polish that edge 1st but wanted to see how much you removed and what you have left.https://www.AR15.Com/media/mediaFiles/369449/20200110_201005_2_jpg-1230316.JPG I just used a Dremel till it worked. Sorry I don't have a more quantitative answer. My ramps go all the way down to the top of the lower. http://c3junkie.com/?page_id=597 
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Posted: 1/11/2020 7:26:09 PM EDT
[#46]
I started this project right as the Endomags started to come out.....in hindsight I would have gone that route for many other reason to include this issue.
I hit the ramps with a file, the block does not seem as hard as I would have thought. A couple mins and I have a knife edge. If it is still not enough I have a couple options. 1) Tig a couple beads under the ledge to build that area up and keep shaping it. 2) Drill a new roll pin hole in the feed ramp and lower receiver to shift the whole block down .03 - .04". Might cause issue at the transition into the chamber. 3) Mill a new block, I was cautious of this at first thinking the original was harder than it was. Thanks for everything you've done for the Cmmg RDBs Amphibian, I just received the A5 tube, Tubbs spring and hydraulic buffer to test as soon as I get this sorted, can't wait. |
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Posted: 1/15/2020 9:42:18 AM EDT
[#47]
Good thread with lots of good info.
I have a factory Banshee upper that I have been using with Endomags on a pistol lower that sees double duty with an 11.5 5.56 upper. That lower has an H3 buffer, which works with the Banshee upper (5 inch). I need to do some more side by side tests. But it feels like the recoil is softer on the 9mm upper when I swap out that H3 buffer for a lighter one. When I get more time and some decent weather I will do some more direct comparisons. I haven't had as much time to shoot lately as I would like. Reliability has been excellent with both factory winchester white box, and my own 124gr handloads. I need to get my Form 1 can going. I bought this with the intention to shoot it suppressed 100% of the time. Fun range gun for rifle like shooting at distances less than 100 yards without damaging all my steel targets. Reliability has been excellent. Ejection started looking a little weak so I emailed CMMG and they sent me out a new ejector spring. Great fast response and customer service. No affiliation whatsoever, but for you guys who shoot a lot. Young Manufacturing has a bolt assembly tool fixture that holds a bolt securely in place and has a threaded plunger that you can use to compress the ejector. Also comes with a punch and a roll pin seating punch. It makes swapping ejectors and springs a two minute job with no cussing or needing 3 extra hands. I ordered mine from Dillon Precision but other retailers carry them. About $50 shipped. It made the job so easy that I replaced the ejector springs on all my high round count 5.56 rifles in about 15 minutes. It is the slickest AR related tool I have used since I bought my Reaction Rod. |
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Posted: 1/16/2020 12:33:47 PM EDT
[#48]
anyone on here used the matador mag x on this? i called them, they said they would return it if it didnt work. they said someone told them that it would work if you removed the ejector. but i feel that thats not quite gonna work,
depends on which bolt they were using? cause if this is made for glocks, dont the glock bolt sit higher than the guard? ie, it will never pick the round up? seems thats what happened when i tried to use the endo mag erroneously purchased for glocks vs the guard... i have made my own redneck cz 75 mag block, but its weird engineering a mag catch... theirs seems pretty good https://shopusa.matadorarms.com/Mag-X_p_73.html |
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Posted: 1/19/2020 4:10:51 PM EDT
[#49]
Quote HistoryQuoted:
Any idea why the lead sled jammed and shoulder fired didn't? Quote HistoryQuoted:
Quoted:...Here is what it looked like with the CMMG recommended buffer/spring configuration, running 115 Gr blazer, it would function fine when shoulder fired but would jam in the lead sled, only 2 rounds fired in the video below... That being said. I have pondered if the spring around the firing pin isn't behaving in some way similar to the inertia spring in Benelli shotguns. Putting an inertia drive shotgun in a rigid fixture will generally cause it to malfunction. I don't know for sure if this is going on. I have a good understanding of how gas operated AR-15s work. I roughly understand how the RDB mechanism works but I still have some questions in my mind about what exactly is going on. |
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Posted: 1/21/2020 9:08:26 PM EDT
[#50]
@amphibian would recommend the 9mm blitzkrieg buffer on a AR45 using the CMMG bolt and barrel setup? I tried messaging you but your inbox is full.
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