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Originally Posted By amphibian: Unfortunately, I haven't shot it since the last SMG match where I had another FTE on the first stage and stopped shooting it so I could take more material off the extractor and test again. Originally Posted By amphibian: Originally Posted By TheGunslinger: @amphibian Any updates with yours? |
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Shot in our local subgun match using a 7.5 inch upper with a New Frontier billet Glock lower running a RDIAS.. Standard spring and buffer tube with an H2 buffer K lifter Glock factory 33 round and a Beta mag used. After 200 rounds of Norma 115gr rounds fired the gun would fail to eject. Emailed Mean so will wait for a a-fix hopefully. |
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Shot about 200 rounds through mine at a USPSA match this weekend. Total round count is a little over 500. Ran like a champ with zero malfunctions. Fiocchi 115gr K lifter Armaspec SRS Gen 4/Carbine buffer with a cutdown recoil spring. The stock spring was oversprung for me, it took about #20 to compress (my Tubbs flatwire took about #14.5). I trimmed the spring till it took about the same force to compress. |
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The fluted chamber is the Achilles heel of the design in my opinion. After a few hundred rounds the bolt is filthy from powder fouling. The failure to eject came after about 600 rounds or so. My ejector can best be described as sticky. It does not pop out after being depressed without some help. Powder fouling and tight fit seem to be the culprit. A really tiny pin holds the ejector so without the proper punch, a replacement pin and the Mean bolt fixture I wouldn't attempt disassembly for cleaning. Instead it going into my ultrasonic cleaner. Not sure a little sanding or polishing of the ejector would help but not going to try in any event. In our monthly subgun match we shoot about 300 rounds. So if the ultrasonic cleaning does the job the bolt will get dunked after each shoot. I will be extremely happy if that will make it run reliably and make my blowback 9MM a wall ornament. |
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After a trip to the ultrasonic cleaner the ejector works freely again. After speaking with Keith from Mean he suggested I send them the bolt to replace the pin and spring. He stated that the pin can be flaired when installed and could cause drag. Also suggested adding oil can free it up if sticking. For me ultrasonic cleaning after each match is not a hardship. As long as I know how to keep it reliable I am happy. |
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Originally Posted By subgunner: After a trip to the ultrasonic cleaner the ejector works freely again. After speaking with Keith from Mean he suggested I send them the bolt to replace the pin and spring. He stated that the pin can be flaired when installed and could cause drag. Also suggested adding oil can free it up if sticking. For me ultrasonic cleaning after each match is not a hardship. As long as I know how to keep it reliable I am happy. I put the picture below on page 2 of this thread before firing it.  I am right at around 1K rounds now and the strength is now down to about 4lbs.... so maybe it is getting a bit weak. |
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Keith told me the ejector spring is stock ar15. Since my bolt is on the way to Mean I can't take a measurement. After 600 rounds it required quite a bit of force to depress it so the spring seems fine. if it's kept clean and lubed I expect it will work okay . Probably replace the spring every few thousand rounds? |
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Originally Posted By subgunner: Keith told me the ejector spring is stock ar15. Since my bolt is on the way to Mean I can't take a measurement. After 600 rounds it required quite a bit of force to depress it so the spring seems fine. if it's kept clean and lubed I expect it will work okay . Probably replace the spring every few thousand rounds? I think 2.5k is too short and was told very conservative numbers but seeing my ejector spring strength went from 8 to 4 lbs at only 1k rounds does have me concerned. Maybe need to divide the 5k by 3 if shooting full auto and suppressed like I am....but even that is like 1667 rounds. I had asked before about getting a go / no-go specification on when to replace springs and never got an answer. If anyone has read my documentation on the CMMG RDB, I consider 5lbs or less is when FTE's start happening. |
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Originally Posted By amphibian: I posted pictures from the manual stating that you need to replace the extractor/ejector springs at 5k and if shooting full auto and/or suppressed to cut that in half. I think 2.5k is too short and was told very conservative numbers but seeing my ejector spring strength went from 8 to 4 lbs at only 1k rounds does have me concerned. Maybe need to divide the 5k by 3 if shooting full auto and suppressed like I am....but even that is like 1667 rounds. I had asked before about getting a go / no-go specification on when to replace springs and never got an answer. If anyone has read my documentation on the CMMG RDB, I consider 5lbs or less is when FTE's start happening. Does the fluted chamber on this platform counter the 5lbs or less for FTEs? |
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Originally Posted By mikego_34: Does the fluted chamber on this platform counter the 5lbs or less for FTEs? Originally Posted By mikego_34: Originally Posted By amphibian: I posted pictures from the manual stating that you need to replace the extractor/ejector springs at 5k and if shooting full auto and/or suppressed to cut that in half. I think 2.5k is too short and was told very conservative numbers but seeing my ejector spring strength went from 8 to 4 lbs at only 1k rounds does have me concerned. Maybe need to divide the 5k by 3 if shooting full auto and suppressed like I am....but even that is like 1667 rounds. I had asked before about getting a go / no-go specification on when to replace springs and never got an answer. If anyone has read my documentation on the CMMG RDB, I consider 5lbs or less is when FTE's start happening. Does the fluted chamber on this platform counter the 5lbs or less for FTEs? The fluted chamber should ease extraction, but I don't see how it would aid ejection. |
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Got my M and P lifters in yesterday. Went to the range to test it out. Had a very interesting issue as my gun was getting so many light strikes almost every other shot regardless of what lifter was installed. So it was basically impossible to test out the recoil impulse since it was basically a single shot when it did fire. I noticed that it was very hard to extract a round when there was a light strike. When cycling the BCG with no ammo, there was a noticeable resistance and click before it went into battery. My original thought was the Armaspec SRS wasn’t going into full battery because i had trimmed the spring to lighten it up. I let my friend shoot it some and verified that on every light strike, the hammer strike would visibly push the BCG into battery. Spiltting the upper and cocking the hammer to fire it would work. At least this verifies that it will not fire OOB. I took the BCG out when I got home to check the lifter/bearing interaction. When pushing the lifter into the bolt, I noticed that one ball was sticking and took some effort to push the lifter in regardless of which lifter I tried. It turned out to be the opening of small circlip that retains the ball bearing was lined up with one of the bearings, so when it unlocked, it pushed the bearing in further and wedged itself in that gap. I took a scribe and pushed the circlip so the opening was not lined up with the bearing. This fixed the sticky bearing issue and all lifters were able to smoothly push the bearing outwards. I’m going to switch back to the Tubbs/carbine buffer in the mean time. The Armaspec has very minimal preload on the bolt due to the 2 spring system. At full extension, the secondary spring is providing the preload on the BCG. It takes about #4.5 pounds of pressure for the BCG to start moving backwards. It was probably enough preload to push the BCG into battery when it was clean (I hadn’t cleaned it until after todays session). I’d have to get some spacers to add some preload. The Tubbs spring takes around #9.5 pounds before it starts moving. So all in all, I learned some stuff about the BCG but nothing about how the lifters felt seeing as it was basically a single shot all day. The good news is that my ejector spring is still strong and has zero ejection issues with 650 rounds through it now. |
| I like the tubbs lightweight flatwire spring in my suppressed 556 as it doesn't sacrifce preload compared to a normal carbine spring but allows me to turn the gas down for a lower bolt velocity and greater bolt unlock delay. I plan on trying that spring along with a light buffer when I get my mean arms upper if I can get lifter that will work with that combo. |
| Shot around another 150 rounds yesterday evening. This time with the Tubbs/Carbine buffer and “P” lifter setup with Fiocchi 115 gr. Gun operated flawlessly and felt really good, this will be my preferred setup. Didn’t get a chance to swap lifter and compare them back to back. My buddies were impressed with how consistent the ejection pattern was. Over 800 rounds in without a single ejection issue to report. |
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Originally Posted By amphibian: https://c3junkie.com/wp-content/uploads/2023/12/ejector-spring2.jpg Was it still ejecting? |
Death to quislings.
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Originally Posted By backbencher: Was it still ejecting? Originally Posted By backbencher: Originally Posted By amphibian: https://c3junkie.com/wp-content/uploads/2023/12/ejector-spring2.jpg Was it still ejecting? |
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Originally Posted By amphibian: It has been unreliable in ejecting. Originally Posted By amphibian: Originally Posted By backbencher: Originally Posted By amphibian: https://c3junkie.com/wp-content/uploads/2023/12/ejector-spring2.jpg Was it still ejecting? It has been unreliable in ejecting. Beginning to think that bolt mounted ejectors are not the answer for delayed blowback systems in the AR. |
Death to quislings.
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Originally Posted By backbencher: Beginning to think that bolt mounted ejectors are not the answer for delayed blowback systems in the AR. Originally Posted By backbencher: Originally Posted By amphibian: Originally Posted By backbencher: Originally Posted By amphibian: https://c3junkie.com/wp-content/uploads/2023/12/ejector-spring2.jpg Was it still ejecting? It has been unreliable in ejecting. Beginning to think that bolt mounted ejectors are not the answer for delayed blowback systems in the AR. You mean to say that Gen. Thompson/Auto Ordnance got it right over 100 years ago? Who'd a thought. MHO, YMMV, etc. Be well. |
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Originally Posted By -k-: Or it could be one bad spring that caused all his problems. I'm interested to hear how it runs with a replacement, and for how long. Pictured below is what MEAN was showing at the 2020 Shot Show which didn't use a spring loaded ejector. I was really hoping the final product would continue to NOT use a spring loaded ejector.  I have done so much testing with the CMMG RDB with a lot of various springs and nothing I found was as strong as the CMMG MK10 spring as it is using thicker gauge wire. I went ahead and put a brand new CMMG MK10 spring in my MEAN bolt and it is measuring around 12 lbs of force. My trigger pull gauge maxes out at 12 so not exactly sure. The same spring in a CMMG bolt is about 11lbs. I tested it today and ran about 4 mags through it and it ran 100%. I am going to run it in the next match and see if it can make it without an FTE. |
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Originally Posted By -k-: Or it could be one bad spring that caused all his problems. I’m interested to hear how it runs with a replacement, and for how long. It could be - but we've similar issues in CMMG's rotary delayed blowback bolts as well. |
Death to quislings.
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Originally Posted By -k-: Yes, but only one example of an ejector spring failure in the MEAN so far. At this point, I have no doubt that if we supplied amphibian with enough ammo, he could probably break ejector springs weekly. It's fascinating that the momentary force on the ejector in locked breech ARs isn't a problem, but the continuous pressure in a delayed blowback system is. |
Death to quislings.
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Shot a little over 90 rounds today at a local mini match. I short stroked it as well. This thing is flat. Like equally as flat if not more than the MPX PCC 16”, which is also a heavier gun I believe. Zero issues once again. Solid ejection. I let a M class/PCC USAF Shooting Team member try it out and was very impressed with how flat it was. He currently shoots a JP GMR-15 and had a MPX with all the go fast parts available. He said the JP-5 wasn’t wasnt a huge difference compared to his tuned GMR-15, but this MEAN Arms gun was super flat and he’s already looking at selling some stuff to pick up an upper  .Took the W today with it   MEAN Arms bearing delay 9mm upper - USPSA 03-09 classifier |
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Originally Posted By backbencher: At this point, I have no doubt that if we supplied amphibian with enough ammo, he could probably break ejector springs weekly. It’s entirely possible that there are not enough out there, with enough rounds to see the problem replicated yet. I’m saying it’s also possible that was just a single bad spring. Probably worth waiting for a bit more data points. |
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Originally Posted By -k-: It’s entirely possible that there are not enough out there, with enough rounds to see the problem replicated yet. I’m saying it’s also possible that was just a single bad spring. Probably worth waiting for a bit more data points. Originally Posted By -k-: Originally Posted By backbencher: At this point, I have no doubt that if we supplied amphibian with enough ammo, he could probably break ejector springs weekly. It’s entirely possible that there are not enough out there, with enough rounds to see the problem replicated yet. I’m saying it’s also possible that was just a single bad spring. Probably worth waiting for a bit more data points. It could be - but the continuous pressure of a case head on an extractor spring in a delayed blowback action is seemingly very different from the momentary pressure of a case head in a locked action. |
Death to quislings.
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Originally Posted By amphibian: Even with a bad spring, I wish the design didn't rely on a spring loaded ejector in the first place. Pictured below is what MEAN was showing at the 2020 Shot Show which didn't use a spring loaded ejector. I was really hoping the final product would continue to NOT use a spring loaded ejector. https://c3junkie.com/wp-content/uploads/2020/04/MeanRollerDelayed-ShotShow2020-1.png I have done so much testing with the CMMG RDB with a lot of various springs and nothing I found was as strong as the CMMG MK10 spring as it is using thicker gauge wire. I went ahead and put a brand new CMMG MK10 spring in my MEAN bolt and it is measuring around 12 lbs of force. My trigger pull gauge maxes out at 12 so not exactly sure. The same spring in a CMMG bolt is about 11lbs. I tested it today and ran about 4 mags through it and it ran 100%. I am going to run it in the next match and see if it can make it without an FTE. Originally Posted By amphibian: Originally Posted By -k-: Or it could be one bad spring that caused all his problems. I'm interested to hear how it runs with a replacement, and for how long. Pictured below is what MEAN was showing at the 2020 Shot Show which didn't use a spring loaded ejector. I was really hoping the final product would continue to NOT use a spring loaded ejector. https://c3junkie.com/wp-content/uploads/2020/04/MeanRollerDelayed-ShotShow2020-1.png I have done so much testing with the CMMG RDB with a lot of various springs and nothing I found was as strong as the CMMG MK10 spring as it is using thicker gauge wire. I went ahead and put a brand new CMMG MK10 spring in my MEAN bolt and it is measuring around 12 lbs of force. My trigger pull gauge maxes out at 12 so not exactly sure. The same spring in a CMMG bolt is about 11lbs. I tested it today and ran about 4 mags through it and it ran 100%. I am going to run it in the next match and see if it can make it without an FTE. The thicker wire in the CMMG spring might result in a lower service life in other applications if it results in the spring being compressed to near solid height every cycle. |
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Originally Posted By castlebravo84: The thicker wire in the CMMG spring might result in a lower service life in other applications if it results in the spring being compressed to near solid height every cycle. This is a viable reason for early spring failure, the constant pressure theory isn’t likely to overstress the spring. |
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Originally Posted By -k-: This is a viable reason for early spring failure, the constant pressure theory isn’t likely to overstress the spring. Originally Posted By -k-: Originally Posted By castlebravo84: The thicker wire in the CMMG spring might result in a lower service life in other applications if it results in the spring being compressed to near solid height every cycle. This is a viable reason for early spring failure, the constant pressure theory isn’t likely to overstress the spring. My theory on the RDB failure mechanism is that the slop in head space results in the ejector pushing the case head out a few thousandths while in battery (but not enough prevent primer ignition), and then upon firing, the case head slams back in into the ejector with enough force to sink it below the bolt face and compress the spring to solid height. A bit off topic for this thread, but has anyone tried a weaker/shorter spring in the CMMG? The Mean Arms bolt shouldn't have that problem, but the Mean ejector is a lot bigger and heavier than the mil spec spring is designed for, so maybe it will have similar symptoms. I haven't got my Mean upper yet so I can't check it out, but if the ejector bottoms out on the bolt head before the spring fully compresses, I don't see why it should have a problem. If the ejector can be pushed in past the bolt face and only bottoms out on the spring hitting solid height, I would expect the spring to wear quickly. |
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Originally Posted By castlebravo84: My theory on the RDB failure mechanism is that the slop in head space results in the ejector pushing the case head out a few thousandths while in battery (but not enough prevent primer ignition), and then upon firing, the case head slams back in into the ejector with enough force to sink it below the bolt face and compress the spring to solid height. A bit off topic for this thread, but has anyone tried a weaker/shorter spring in the CMMG? Originally Posted By castlebravo84: My theory on the RDB failure mechanism is that the slop in head space results in the ejector pushing the case head out a few thousandths while in battery (but not enough prevent primer ignition), and then upon firing, the case head slams back in into the ejector with enough force to sink it below the bolt face and compress the spring to solid height. A bit off topic for this thread, but has anyone tried a weaker/shorter spring in the CMMG? As mentioned in the link above, I have tried several different springs. Including the HK 416 braided wire ejector spring. The CMMG MK10 lasts the longest IME.  9mm CMMG RDB Headspacing The Mean Arms bolt shouldn't have that problem, but the Mean ejector is a lot bigger and heavier than the mil spec spring is designed for, so maybe it will have similar symptoms. I haven't got my Mean upper yet so I can't check it out, but if the ejector bottoms out on the bolt head before the spring fully compresses, I don't see why it should have a problem. If the ejector can be pushed in past the bolt face and only bottoms out on the spring hitting solid height, I would expect the spring to wear quickly. As I mentioned early on in this thread, I didn't detect the headspace slop with the MEAN like the CMMG RDB has but again, compare this to a straight blowback 9mm which uses a fixed ejector and an extractor that is made from spring steel and very rare to ever hear of either failing or wearing out. Yes, the MEAN is way softer than a straight blowback 9mm...but was hoping it would do that retaining the reliability of the a straight blowback 9. I am going to see how long I can go before I start having malfunctions again. I plan on making it to the next SMG match and will run it then but as soon as I have a single malfunction, I'm going to switch guns. Last match it had an FTE in the first stage and went back to an Uzi but it probably had the broken ejector spring at that time. |
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Shot another 120 rounds yesterday to test out some new buffer configurations. First configuration: Short stroked Armaspec SRS Carbine buffer with nylon spacer from Home Depot and an additional spacer for the secondary spring to increase preload on the BCG. I did not encounter any light strikes with it this time. I’d have to say this reduced muzzle movement like 10% compared to the short stroked Tubbs AR flatwire/carbine buffer setup.  Second configuration: Short stroked Tubbs AR spring and Kynshot 5000HP. My friend had one that he was not going to use so I asked if I could try it out before he returned it. My oh my. I thought my gun was flat before but this combo was even flatter. I did 6 shots of doubles at 15 yards and could cover the entire 12 rounds group with just 3 pasters. I was almost stacking bullets on bullets with the doubles BCG stroke bottomed out. Buffer is not bottomed out  BCG and Kynshot buffer fully bottomed out 
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Originally Posted By mikego_34: How hard is it to change the ejector spring should it fail? Seems like its not that big of a deal to me but could be wrong. Also, any updates @amphibian ? As I posted in this thread, I swapped the ejector spring out for a CMMG MK10 ejector spring which is the strongest ejector spring I've seen and it went from 12lbs new to around 4lbs in less than 300 rounds. I also started to have FTE's again which also prompted me to check the strength. I am shelving my MEAN upper for now. Others don't seem to be having the same issues I am so I will chalk it up to me trying to achieve slow full auto cyclic rates which it can do but I think stresses the ejector spring more. |
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Originally Posted By amphibian: Not a big deal to swap the ejector spring. As I posted in this thread, I swapped the ejector spring out for a CMMG MK10 ejector spring which is the strongest ejector spring I've seen and it went from 12lbs new to around 4lbs in less than 300 rounds. I also started to have FTE's again which also prompted me to check the strength. I am shelving my MEAN upper for now. Others don't seem to be having the same issues I am so I will chalk it up to me trying to achieve slow full auto cyclic rates which it can do but I think stresses the ejector spring more. Have you by chance measured how deep the ejector spring channel and compressed spring height + ejector is? I wonder if you’re getting coil bind which is breaking your ejector springs. I’ve since shot 2 local matches and let a couple of people try it out since my last update. Zero issues to report. |
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Originally Posted By tt350z: Have you by chance measured how deep the ejector spring channel and compressed spring height + ejector is? I wonder if you're getting coil bind which is breaking your ejector springs. Originally Posted By tt350z: Originally Posted By amphibian: Not a big deal to swap the ejector spring. As I posted in this thread, I swapped the ejector spring out for a CMMG MK10 ejector spring which is the strongest ejector spring I've seen and it went from 12lbs new to around 4lbs in less than 300 rounds. I also started to have FTE's again which also prompted me to check the strength. I am shelving my MEAN upper for now. Others don't seem to be having the same issues I am so I will chalk it up to me trying to achieve slow full auto cyclic rates which it can do but I think stresses the ejector spring more. Have you by chance measured how deep the ejector spring channel and compressed spring height + ejector is? I wonder if you're getting coil bind which is breaking your ejector springs. The fact that the manual calls out the lifespan for the ejector and extractor springs at 2,500 rounds for full auto OR suppressed shooters is just too low for me. I've since shot 2 local matches and let a couple of people try it out since my last update. Zero issues to report. I am waiting on some raw materials for another delayed blowback upper right now that doesn't have these ejector spring caveats.....if that fails, then I will probably work on the MEAN again or if they make any improvements that I think will extend the life, I would be interested. |
| I got my 7.5" upper in and have been playing with it. I shoot suppressed with 150gr syntech, which is a fairly weak load. I was able to get it to run that weak ammo with the L lifter using a tubbs lightweight flatwire spring and taccom ultralight buffer. It would also kinda run with the R lifter, but it wouldn't lock back, and would occasionally fail to go fully into battery resulting in no primer strike. It was very soft shooting, and was FAR quieter suppressed than my straight blowback upper. The R lifter made it even more quiet. I might try a JRC extended tube and cut down a standard carbine flatwire spring. I should be able to get the bolt closed force down to the same as the lightweight flatwire (which is itself about the same as a standard milspec carbine spring), but the bolt open force would be a bit lower hopefully allowing the R lifter to fully cycle it. |
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We're still getting the word out to more people about the Bearing Delay upper. We did add a Layaway option for people who don't want to spend the full price right away. The video from PSR that came out on Christmas Eve has helped and we have some additional reviewers lined up who should be posting in the future.  New Delayed Blowback Just Dropped Thanks to all of our customers and people who have supported MEAN. |
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@MEAN_Arms Is selling a complete bolt assembly something you would consider doing? I think the availability of a spare bolt would be a great option for competitors. I know that ejection issue is the most talked about issues and this would greatly alleviate those concerns when traveling out of state for matches. Nobody is gonna want to try to swap ejector/extractor springs during a match, but a bolt swap would be no problem. |
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Originally Posted By tt350z: @MEAN_Arms Is selling a complete bolt assembly something you would consider doing? I think the availability of a spare bolt would be a great option for competitors. I know that ejection issue is the most talked about issues and this would greatly alleviate those concerns when traveling out of state for matches. Nobody is gonna want to try to swap ejector/extractor springs during a match, but a bolt swap would be no problem. I agree...this sounds like an EXCELLENT idea!! |
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Finally got to try out a CMMG radial delayed gun today. One of the guy I shoot with had a Banshee that basically wouldnt eject. I told him I’d take a look at it and found that his ejector only had like #3 of pressure. I pulled the ejector spring out and it was considerably shorter than a new spring. He said he only had like 300 rounds through that spring since he replaced the original spring for ejection issues. The MEAN Arms blows the CMMG out of the water in all shooting attributes. It is way softer, flatter, and way more consistent ejection. The only thing the CMMG has the MEAN Arms best is cost, but I am so glad that I spent the extra money on the MEAN Arms. I haven’t added any new update simply because this thing has been running perfectly with zero malfunctions or quirks. It’s been used for matches twice a month and has not been cleaned since I switched to the optional lifter back in December 2023. |
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Originally Posted By tt350z: Finally got to try out a CMMG radial delayed gun today. One of the guy I shoot with had a Banshee that basically wouldnt eject. I told him I’d take a look at it and found that his ejector only had like #3 of pressure. I pulled the ejector spring out and it was considerably shorter than a new spring. He said he only had like 300 rounds through that spring since he replaced the original spring for ejection issues. The MEAN Arms blows the CMMG out of the water in all shooting attributes. It is way softer, flatter, and way more consistent ejection. The only thing the CMMG has the MEAN Arms best is cost, but I am so glad that I spent the extra money on the MEAN Arms. I haven’t added any new update simply because this thing has been running perfectly with zero malfunctions or quirks. It’s been used for matches twice a month and has not been cleaned since I switched to the optional lifter back in December 2023. Thanks for posting! |
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Originally Posted By tt350z: Finally got to try out a CMMG radial delayed gun today. One of the guy I shoot with had a Banshee that basically wouldnt eject. I told him I’d take a look at it and found that his ejector only had like #3 of pressure. I pulled the ejector spring out and it was considerably shorter than a new spring. He said he only had like 300 rounds through that spring since he replaced the original spring for ejection issues. The MEAN Arms blows the CMMG out of the water in all shooting attributes. It is way softer, flatter, and way more consistent ejection. The only thing the CMMG has the MEAN Arms best is cost, but I am so glad that I spent the extra money on the MEAN Arms. I haven’t added any new update simply because this thing has been running perfectly with zero malfunctions or quirks. It’s been used for matches twice a month and has not been cleaned since I switched to the optional lifter back in December 2023. What lifter exactly did you switch to and why? |
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Anyone pull the barrel and have pictures? I need to get a MP5-SD integral barrel mounted to this thing, and was hoping it was more of a "turn some threads on a regular barrel for the roller extension" and not a "machine all kinds of weirdo interlocking parts" kind of thing. i have the integral SD on a CMMG RDB build and have one on blowback that I was hoping to move to this upper. maybe I'll pull my barrel this weekend. |