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[ARCHIVED THREAD] - Full Auto CMMG Guard Tuning (Page 3 of 4)
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Quoted:
Before I left the range, I put a Tubbs in there and ran another 30 round Endomag. Felt it and it had already weakened considerably. I took it apart when I got home and it was deformed like all the other ones I've worn out before. Every ejector spring I've tried have all suffered the same fate and none seem any stronger in the Guard. I've tried, no name ones, Sig, Wilson Combat, Tubb, Sprinco....none seem to be able to last that long in the Guard when tuned to run this slow. |
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Quoted: So I got this done...
On the left is the Guard 9mm bolt, the two in the middle are 5.45 bolts that I had my buddy turn down on his lathe so they match the Guard and fit in the Guard carrier and the spring goes over the tail of the bolt. On the right is a 556 bolt for comparison showing the radius that needed to be removed. http://c3junkie.com/wp-content/uploads/2019/01/545-mod.jpg I used a Dremel to grind a less aggressive angle on the lugs. It is amazingly smooth and a super slow RoF suppressed...In this case my Gemtech MK9K. This is with NO weight in the carrier, 9mm Kynshot, 300 BLK Tubb flat spring and A5 buffer tube. http://c3junkie.com/wp-content/uploads/2019/01/545-mod-504RPM-MK9k-1024x487.jpg I think this is the slowest and smoothest closed bolt 9mm SMG I've every fired.....downside is that I think with the Guard system, the more you try to delay it, the faster it kills the ejector spring. My modified 5.45 bolt and the ejector spring that was new after about only 100 rounds. (3) 30 round mags and a few singles that I fired to figure out the right angle to use. The ejector spring was beat up so bad that there was no tension on the ejector...it was flopping around in the bolt. http://c3junkie.com/wp-content/uploads/2019/01/545-mod-ejector-spring-100rund.jpg If only the Guard had a fixed ejector.....I'm eyeballing my Sig MPX to see what kind of surgery could be done on the Guard to get a fixed ejector on it like the MPX.... 
What if you don't have a fixed ejector - what if it's just a rod in the ejector channel as now, but run that channel and ejector rod completely through the bolt - and, and, you get some ants to hit that rod as hard as they can w/ a hammer @ the end of the bolt carrier stroke. Or, you have a fixed point in the receiver, that hits one end of the pinned hammer, and the other end hits that rod, instead of using ants? Or, since it's delayed blowback, get rid of the extractor, maybe it would take some stress of the ejector? Or maybe we tap a little gas off the bbl, and run a rod off of that, and that will hit the pinned hammer in the bolt carrier really hard, and whack that rod very hard, and you'll have the 1st gas-piston operated ejector on a delayed-blowback firearm EVAR!
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Quoted: Holy crap, dude! Lemme come up w/ some more zany ideas for you to try!
What if you don't have a fixed ejector - what if it's just a rod in the ejector channel as now, but run that channel and ejector rod completely through the bolt - and, and, you get some ants to hit that rod as hard as they can w/ a hammer @ the end of the bolt carrier stroke. Or, you have a fixed point in the receiver, that hits one end of the pinned hammer, and the other end hits that rod, instead of using ants? Or, since it's delayed blowback, get rid of the extractor, maybe it would take some stress of the ejector? Or maybe we tap a little gas off the bbl, and run a rod off of that, and that will hit the pinned hammer in the bolt carrier really hard, and whack that rod very hard, and you'll have the 1st gas-piston operated ejector on a delayed-blowback firearm EVAR! 
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Smoother. Like I mentioned, it is the smoothest closed bolt SMG I've ever fired...and I've fired a lot. Quoted:
-How smooth compared to the MP5? Thanks for the additional info. Time to dig out my 5.45 bolt..... |
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Quoted: Sarcasm? Some of it sounds reasonable, like the ants with their tiny hammers.  So, ants!
Which brought me to the pinned hammer. The gas piston operated hammer was the ancient German engineer in me.
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Thanks for the additional info. Time to dig out my 5.45 bolt..... Since I'm running Endomags, this is a non-issue. Shouldn't be an issue for someone that has gone through the trouble to get Colt mags to work with the Guard but IMHO, Colt mags require too much force to strip rounds vs Glock or the Endomags which is going to make for a smaller window of reliability when trying to get things tuned to run this slow. |
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Not yet...the extremely short ejector spring life is still a problem. Quoted:
Not yet...the extremely short ejector spring life is still a problem. Quoted:
Oh...also wanted to mention...remember that if you want to try what I'm doing, it won't work with Glock mags since the Guard bolt is more narrow to clear the feed lips of a Glock mag. Since I'm running Endomags, this is a non-issue. Shouldn't be an issue for someone that has gone through the trouble to get Colt mags to work with the Guard but IMHO, Colt mags require too much force to strip rounds vs Glock or the Endomags which is going to make for a smaller window of reliability when trying to get things tuned to run this slow.  Double stack, single feed, <$20/each. Downside is they have to be opened up slightly to clear even the Guard bolt lugs. So prob a no go with a 5.45 bolt unless I trim the bottom two lugs to match the Guard's profile. Oh, and they only fit into my Polymer80 lower; slightly too wide for a standard aluminum lower. Oh, and they need a custom mag adapter. Geez on second thought maybe they're a terrible idea.  . But hey, they've been working ok so far so I'm happy.
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True, but I could accept replacing a spring every 1k rounds or so if it meant having a 9mm AR that shoots as soft...nay, softer than an MP5. To me that was a huge milestone. So again, well done! Yessir, no Glock mags for me. I'm still tinkering with Colts but found another cheap option - Tapco Masterpiece/Sten mags: https://17g3xk34ahga1v23q91j8y5oxka-wpengine.netdna-ssl.com/wp-content/uploads/2014/05/mpa20-70p-polymer-magazine.jpg Double stack, single feed, <$20/each. Downside is they have to be opened up slightly to clear even the Guard bolt lugs. So prob a no go with a 5.45 bolt unless I trim the bottom two lugs to match the Guard's profile. Oh, and they only fit into my Polymer80 lower; slightly too wide for a standard aluminum lower. Oh, and they need a custom mag adapter. Geez on second thought maybe they're a terrible idea. . But hey, they've been working ok so far so I'm happy.That looks like too much work to use those mags...you don't like the Endomag option? |
I got some carbide drill bits and opened up the ejector hole of my 5.45 bolt to take the 308 ejector spring.
It is a huge hole compared to the 556 ejector spring hole. So big that the hole broke into the FP hole. With the extractor removed you can see the ejector spring now. 
Comparison of ejectors.....L-R....Palmetto PA10 Ejector, 5.56, crude ejector made from 5/32 drill bit shank.  I did have to trim the spring down 
Ejector installed in modified 5.45 bolt. 
Tried it out and had to do some fine tuning on the ejector fitment and after I thought I had it worked out it killed the spring in about 20 rounds. So bad that the spring had no tension like the 556 spring I had tested before. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I also tested my spring loaded weight with an SWR 40SW can and a .45 Gemtech Blackside can. Interestingly, these both work fine whereas any other 9mm can I have tested makes my setup w/ the spring loaded weight a single shot. (I have tested, 9mm Liberty Mystic, 9mm SWR Trident, Octane 9 and Gemtech MK9K). Pictured below is the RoF with the .45 Gemtech Blackside. The Pact Timer counted 581 RPM while the Competitive Edge timer picked up 577 RPM....both counted 10 rounds. I had previously gotten 564 RPM unsuppressed with the same exact setup. 
I fired a couple full 30 round mags and I had one malfunction...another failure to eject. I'm trying to get my buddy that is a manufacturer put his fixed ejector in one of my Guard upper and then will have to work on getting the bolt and carrier modified for the fixed ejector. He is the manufacturer that I worked with a few years ago on a prototype 9mm piston upper. I shot his piston upper in full auto and it is really smooth as well, he has a few more bugs to work out on it and he hasn't given me to go ahead to discuss it publicly yet but if he does I will be sure to share it here. I say all this because I know some of you may want to replicate the fixed ejector and I'm not clear as to how much detail he wants me to share on that yet. I'm pretty sure it will cure all the problems I've been having as it is almost identical to what he and I dealt with a few years ago and the fixed ejector clearly fixed the issues we had w/ the 9mm piston upper. |
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Yeah, but the spring isn't making it past 100 rounds....forget 1K rounds. That looks like too much work to use those mags...you don't like the Endomag option? 
As for Endomags, I’d already bought the Tapco mags and heavily vested in the R&D to get them to work. Had I tried Endos sooner I most definitely would’ve gone that route especially with the great success folks have had with them. Plus I’m too stubborn to toss everything in the parts bin and start over! |
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Op,
This is fucing ridiculous! You dremmeled a new bolt and made something better than an mp5!! Anyaay, see this pjc Attached File See the springs rods, as the carrier goes back they protrude towards the bolt area. Is there some waty to do a rod like thst which would protrude thru the carrier like that which could hit the L side of the case head maybe?? |
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Thanks for the suggestions guys but I believe a fixed ejector in the upper is the answer. It is the way Sig did it for the MPX as did my C2 friend. He actually already mounted the ejector in my upper. It looks very nice!
Now I just need to get the bolt and carrier mod'ed to clear the fixed ejector. |
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Would an Olympic type fixed ejector in the upper fit? |
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I have been reading this thread in interest and it would be interesting if we could ever root cause the ejector spring failures as the design seems to work just fine in a rifle caliber.
It certainly seems like the ejector body is acting like a piston and crushing the ejector spring. I presume this is not happening just because of the cartridge compressing the spring as that is really no different from the normal 5.56 variant. It seems like the initial rearward recoil is sending the ejector back with significant velocity to depress and crush the spring (which seems counter intuitive given the reduced recoil the Guard is supposed to produce) or somehow gas is getting around the cartridge and acting on the ejector making it a piston (which seems less likely) I have heard that the Guard also like to consume firing pins as well which tells me there is probably something with the bolt velocity that is off and breaking moving parts inside the BCG assembly. I wonder if instead of just trying to beef up the spring if it would make sense to get an ejector made out of a lighter weight material like titanium which is ~50% the weight of steel. That should in theory put less stress on the ejector spring given the mass it has to support on the recoil stroke. Given how fast the 308 ejector spring died, you wonder if the larger 308 ejector (with more mass) is a bigger contributor to the issue than the overall strength of the spring. It would be interesting to see the bolt velocity with a high speed camera. Obviously this would require destroying a carrier to make cutout so you could actually see the rearward bolt velocity as it spins and recoils inside the carrier itself. |
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It certainly seems like the ejector body is acting like a piston and crushing the ejector spring. I presume this is not happening just because of the cartridge compressing the spring as that is really no different from the normal 5.56 variant. >>>>>>>>>>>>>>>>>>>>>>>>> I know I had mentioned before that if you put a rod down the bore and push on the bolt it would rotate right away which I know did before...well I did this again before cutting the lugs to get a feel for how much to do. I first did it again with the factory Guard bolt and it locked up and didn't move...like the MP5 does. I had to give it a light tap with a hammer to unlock the bolt. This was with both of my Guard uppers. I also felt the bolt move about a mm or so before the lugs of the bolt would hit the extension lugs. I think with this gap that when the round is fired that it launches the ejector inside the bolt...which kills the spring. I also noticed the ejector retaining pin was notched pretty hard...may get sheared off if shot more. >>>>>>>>>>>>>>>>>>>>>>>>> I think that this is worse when trying to slow down the BCG down with heavy buffers or in my case changing the lug angles.....either way, I think going to a fixed ejector will fix all these issues...I hope. I don't think this is happening on 556 because the bolt is actually locked and ejector movement doesn't occur till the pressure has gone down so it doesn't experience the 'shock' like what is happening in the Guard. |
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If I am reading your post correctly “ I also felt the bolt move about a mm or so before the lugs of the bolt would hit the extension lugs” …..you can push on the bolt with a cleaning rod and feel some rearward movement of the bolt before the angled lugs appear to engage the corresponding lugs on the barrel extension?
I wasn’t 100% sure when I initially read this as you mentioned you had to tap the bolt to get it to initially rotate (which implies it was locked tight), but understand now that the two actions may be mutually exclusive. i.e. you get a mm or so of rearward movement before the angled lugs engage and then need an additional tap to get the rotation to start and allow the gun to unlock. If this is the case and the bolt has some free rearward movement, the closest analogy I can think of is an HK rollerlocked gun where the bolt gap has gone to zero and now the bolt can launch backwards unimpeded until the rollers hit the locking piece forcing the rollers to violently engage the trunion…which is a recipe for breaking stuff. From a physics perspective rearward bolt speed by itself won’t crush the spring with the ejector….. it the fast rearward motion coupled with an abrupt stop that sends the ejector rearward compressing the spring. Similar to a human in a car accelerating, you are pushed back into the seat under acceleration and its not until you hit something solid that your body (i.e. the ejector) is thrown in the same linear direction of the initial movement crushing the airbag (i.e. spring). It would make sense that if the bolt is allowed to recoil backward at an extremely high rate of speed and then effectively hits something to impede its rearward movement (i.e. when the bolt lugs initially engage the barrel extension) that the ejector will continue its high speed momentum rearward compressing the ejector spring. You may then get a second rearward momentum impact when the lugs on the bolt clear the lugs the barrel extension and the bolt speeds backwards once again until it effectively bottoms out on the carrier and pushes the whole bolt carrier assembly backwards. The more mass you put in the buffer/carrier the more abrupt/harsher the impact of the bolt into the carrier as the carrier is now heavier and takes longer to start its rearward momentum. Finally you get a 3rd impact once the carrier hits the rear of the buffer tube but at that point the speed is greatly reduced. Normally on a rifle caliber gun this isn’t an issue as the bolt is being pulled backwards by the carrier via the gas injected into the carrier key and headpace is critical on a rifle caliber so the bolt is locked tight. Rearward momentum isn’t an issue for the ejector on a rifle as the bolt stays stationary from a linear movement perspective until it unlocks and then begins its rearward travel with the carrier by being pulled out of the barrel extension by the carrier (vs. slamming into the carrier and pushing the carrier rearward on the guard). This could also explain some of the firing pins breaking as well as the bolt and firing pin have that same high speed acceleration rearward shoving the firing pin directly into the hammer. This isn’t an issue on a blowback AR gun as the firing pin is spring loaded (returning it rearward away from the cartridge) and too short to make a direct connection between the cartridge and the hammer. I agree that the best option is probably a fixed ejector solution or some sort as long as it doesnt compromise the bolt head too much. |
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you get a mm or so of rearward movement before the angled lugs engage and then need an additional tap to get the rotation to start and allow the gun to unlock. Quoted:
you get a mm or so of rearward movement before the angled lugs engage and then need an additional tap to get the rotation to start and allow the gun to unlock. This isn't an issue on a blowback AR gun as the firing pin is spring loaded (returning it rearward away from the cartridge) and too short to make a direct connection between the cartridge and the hammer. I've seen pics of another members Guard bolt and the FP hole was drilled off center. His FP tip broke which I think is because of the hole being off center. FP tip still in primer while bolt rotates and snaps it. I've had a couple break but they didn't break at the tip....I haven't broken another one since replacing them so don't know if CMMG just got a bad lot or what. |
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It would seem to be down to the very different action of the Guard.
In a normal gas-unlocked AR, at firing, the base is pressing against the ejector, but the bolt isn't moving until pressure drops, and as the cartridge is extracted from the chamber, it's actually pulling away from the bolt face as the case walls drag on the chamber, and it's pulled out by the extractor. With the Guard, it is the pressure of gas inside the case that is forcing the case out of the chamber - the extractor is only useful during manual case extraction. The Guard should run fine w/o an extractor at all. On firing, the case head presses against the bolt face, which immediately begins to rotate and move rearward. The case is ejecting itself from the chamber under gas pressure, squashing the ejector flat. Only when the case entirely clears the chamber can the ejector overcome the pressure of the case head and move. I agree w/ OP that a fixed ejector offers the best hope in this situation. The alternative would be a mechanically driven ejector within the bolt, which might require ants with tiny hammers. |
| Not to derail your fixie solution, but is it possible to use an ejector with a leg that protrudes farther into the spring that would bottom out in there when the ejector was flush w the breech face to prevent it from flying down and over compressing the spring? Does that make sense what I am saying? |
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Not to derail your fixie solution, but is it possible to use an ejector with a leg that protrudes farther into the spring that would bottom out in there when the ejector was flush w the breech face to prevent it from flying down and over compressing the spring? Does that make sense what I am saying? Edit: Don't the roll pin and the notch in the ejector restrict ejector motion? How can the spring over-compress? I must be missing something basic because even with all the explanations I still don't understand the mechanism of how the spring is being worn out so fast. |
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That sounds like a good idea. Maybe insert something inside the spring to stop it from over-compressing? Edit: Don't the roll pin and the notch in the ejector restrict ejector motion? How can the spring over-compress? I must be missing something basic because even with all the explanations I still don't understand the mechanism of how the spring is being worn out so fast. Quoted:
Quoted:
Not to derail your fixie solution, but is it possible to use an ejector with a leg that protrudes farther into the spring that would bottom out in there when the ejector was flush w the breech face to prevent it from flying down and over compressing the spring? Does that make sense what I am saying? Edit: Don't the roll pin and the notch in the ejector restrict ejector motion? How can the spring over-compress? I must be missing something basic because even with all the explanations I still don't understand the mechanism of how the spring is being worn out so fast. I think I posted before that the ejector retaining pin was getting hammered and looked like it was bout to shear off which BTW, I failed to mention that with my limited testing w/ the 308 ejector spring that it actually did shear off the ejector pin in the first 10 rounds or so and then I swapped it for a new pin. Then ran the 20 rounds which then killed the spring. Going the 308 ejector spring route does give a larger spring ID to do what you propose but at this point, I've got my Guard upper getting delivered to me today w/ a new fixed ejector that I want to play with. If this works out, I hope to have my friend do my other Guard upper as well and just give up on the ejector in the bolt. You guys know I like to tinker but I do want to get a stable/reliable state and then stop. I have a lot of various uppers that I've tinkered with and have everything dialed in the way I want with the exception of maybe 1 other upper. I don't like having setups where I am always worried about something wearing out. I just want to grab a specific configuration and have some confidence it is going to work with no tinkering. If I stayed with the spring loaded ejector and slow fire setup, I would always be worried about having to periodically check on the ejector health. |
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I paraphrased a bit here for clarity:
Quoted:
I've got my Guard upper getting delivered to me today w/ a new fixed ejector that I want to play with. If this works out, I hope to have my friend do my other Guard upper as well and just give up on the ejector in the bolt. You guys know I like to tinker but I do want to get a stable/reliable state and then stop. Quoted:
I've got my Guard upper getting delivered to me today w/ a new fixed ejector that I want to play with. If this works out, I hope to have my friend do my other Guard upper as well and just give up on the ejector in the bolt. You guys know I like to tinker but I do want to get a stable/reliable state and then stop. re. pin in the ejector spring: Quoted:
Yeah, I had considered that with the 556 ejector but the ID is about the size of a sewing needle. Going the 308 ejector spring route does give a larger spring ID to do what you propose. How about using a titanium or chromium pin in the ejector spring? If it doesn't shatter or deform will it work? How long would the pin (or leg on the ejector if that option is better) have to be to stop the ejector at the right position? Is the .308 spring compatible with the Guard bolt? Thanks. |
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help us determine a simpler solution to the spring fatigue (if there is one). Quoted:
help us determine a simpler solution to the spring fatigue (if there is one). Take your scenario for example....you are using the RB5005, round spring and carbine buffer. I have done very little testing w/ the RB5005 and also prefer the Tubb flat spring and A5. I'm not going to spend the time testing your selected components..... No offense, but I don't have much time these days to tinker like I used to. If you want to stick to those components then you need to figure that out yourself. However, you can use my data points for reference. I think my setup is slower than yours and probably softer shooting and in turn, I think your ejector spring is going to last longer than mine. I have my reasons why I have selected my components and have no desire to change them unless I have a specific configuration that warrants that change. How about using a titanium or chromium pin in the ejector spring? If it doesn't shatter or deform will it work? How long would the pin (or leg on the ejector if that option is better) have to be to stop the ejector at the right position? Is the .308 spring compatible with the Guard bolt? |
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I don't think it is that simple. Take your scenario for example....you are using the RB5005, round spring and carbine buffer. I have done very little testing w/ the RB5005 and also prefer the Tubb flat spring and A5. I'm not going to spend the time testing your selected components..... No offense, but I don't have much time these days to tinker like I used to. If you want to stick to those components then you need to figure that out yourself. However, you can use my data points for reference. I think my setup is slower than yours and probably softer shooting and in turn, I think your ejector spring is going to last longer than mine. I have my reasons why I have selected my components and have no desire to change them unless I have a specific configuration that warrants that change.I guess Titanium in theory would help but I'm not going to mess with that. I would say the same but you need to figure out a way to prevent it from beating up the spring. Did you see all those pictures I posted above?? The Guard bolt's ejector pin hole is basically the same as a 556 ejector pin hole so no way. I had to hog it out huge to get the 308 spring to fit and you can read that was all a failure. I saw your pics of drilling out a different bolt so I wasn't sure about the .308 spring in the Guard. Thanks for clarifying. I'm curious about how to reduce the spring wear for all of us Guard fans so maybe someone else knowledgeable can try a few things before giving up on it. I don't want to have ejection problems pop up without warning either. |
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So I got my buddy to hook me up with a fixed ejector mounted to the upper and a bolt clearanced for the fixed ejector.
I had to cut the angles of the lugs of this new bolt and I guess maybe I cut too aggressive so my RoF went up a bit but still very acceptable. Below is unsuppressed. 9mm Kynshot, A5 tube and 300BLK flat spring. 
Same as above but with 9mm Gemtech MK9K. 
Fixed ejector is the BOMB! Fixed all my ejection issues. I think I ran about 6 mags through it yesterday. Running very well but now I see the spring at the tail of the bolt is dying but it doesn't seem to be an issue. I think the purpose of that spring is to prevent slam fires. So I replaced it with a spring of unknown origin that I had in my box....but again, I don't think it is a big deal especially in a SMG. The extractor spring now seems to be taking a beating. When I went to check it, the extractor pin had actually broken but it was still working. As 'backbencher' posted before, I agree that I don't think the extractor is needed for anything other than for manually extracting a live round. I am going test test firing the Guard w/ the no extractor next time to confirm. Today, I went to a SMG match. It had 4 stages. It was 3 - 4 mags per stage. I ran the entire match suppressed with an Octane 9. One of my friends I went with brought a full auto MP5SD and it gave him some issues and he used my Guard for 2 of the 4 stages. So ran 6 stages w/ a minimum of 3 mags per stage so I'd say 600-700 rounds today with many bursts of of full auto. So out of the 600-700 or so rounds I had two malfunctions. 1. One of my reloads didn't have a primer so not the guns fault. 2. When my buddy was running the Guard, he had 1 double feed. So I would say really only 1 malfunction and with a double feed, who knows what that was about. I don't know if I can really say what happened there. I mean many guns can have occasional double feeds. I used the Endomags the entire time. Looking everything over, I see a good bit of carbon build up in the extension area but not enough to stop the gun from running. I had replaced the extractor spring yesterday with a relatively new 'gold' Colt extractor spring and it is really weak now but the pin hasn't broken and had no extraction issues so I'm just going to keep running it weak and see what happens. The unknown spring I put in the tail of the bolt is worn out like the original Guard one but no slam fires so not too concerned with that either. I'm really happy so far and now it is just a matter of running it more. I'm suspecting that CMMG's original statement of coming out with 8 or so calibers for the Guard is being hindered by the ejector in the bolt. 9mm has higher pressures than 45 which is why I think the .45 doesn't have these issues. I think if they tried to do a Guard in 10mm or 40SW it would be killing the ejector spring very quickly. So maybe CMMG will do a fixed ejector for these higher pressure calibers and maybe offer a retrofit for those with 9mm? |
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What pressures is their 5.7x28mm model running? It's the easy route to a pistol/carbine sibling pair w/ bullets over 2100 fps from the pistol. Higher pressure but maybe not enough mass/inertia to cause all the issues we are seeing in 9mm...which I think would be exacerbated with 40 SW, 10mm etc... My thought is that they may not have any incentive to do a fixed ejector for 9mm for the handful of people that run full auto suppressed but if going to a fixed ejector will then allow them to do the higher pressure calibers then that should give them the incentive to start going down that path. So if we do see them offer 10mm, 40SW, 357 SIG w/ a fixed ejector configuration in the future, they should be able to easily offer those parts to 9mm owners. |
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Thanks dforbthe update!
Cant figure why the extractor spring is getting worn out in particular...maybe something about the rotation soeed of the bolt making it gonout w Centripetal force? Consider using a black M4 extractor spring insert rubber nub?? The soring on the bolt tail, presses against the firing pin like on an armalote AR10? I guess that jump back at ignition is making the spring collapse. I gather that ~1mm clearance that allows that initial jump back w the bolt is necessary to be there so the gun will unlock?? |
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Thanks dforbthe update! Cant figure why the extractor spring is getting worn out in particular...maybe something about the rotation soeed of the bolt making it gonout w Centripetal force? Consider using a black M4 extractor spring insert rubber nub?? The soring on the bolt tail, presses against the firing pin like on an armalote AR10? I guess that jump back at ignition is making the spring collapse. I gather that ~1mm clearance that allows that initial jump back w the bolt is necessary to be there so the gun will unlock?? MHO, YMMV, etc. |
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Quoted: The CMMG published patent application is a detailed explanation, including drawings, of their Guard system. See, U.S. Published Application 2018/0142972. MHO, YMMV, etc. |
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Consider using a black M4 extractor spring insert rubber nub?? Quoted:
Consider using a black M4 extractor spring insert rubber nub?? Right now have the Colt 'gold' extractor spring w/ the black insert in there. I gather that ~1mm clearance that allows that initial jump back w the bolt is necessary to be there so the gun will unlock?? Just seems to me that any attempt to slow it down over the factory recommended buffer/spring/carrier weight will just end up accelerating the wear of the ejector/extractor/bolt springs. One of my friends that was also at the last SMG match was also running a 9mm CMMG Guard and his went down. I don't think he completed the match (he wasn't in my squad so didn't get to see him shoot). He just told me later his ejector spring died. He was running the 9mm Kynshot, 556 Tubb flat spring and A5 w/ a PSA Glock lower and RDIAS. I think he was running suppressed as well. I know he was running it for a while in this configuration so not sure how many rounds he put through it before it went down. |
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I've always been using an extractor spring w/ an insert (black or blue) .....except when I tried the Tubb extractor spring which says not to use it. Right now have the Colt 'gold' extractor spring w/ the black insert in there. I never tried testing the 'gap' in a brand new unfired Guard BCG barrel combo to see what it felt like so don't know if there is a gap after break in or what....or maybe it just gets worse/bigger over time? Just seems to me that any attempt to slow it down over the factory recommended buffer/spring/carrier weight will just end up accelerating the wear of the ejector/extractor/bolt springs. One of my friends that was also at the last SMG match was also running a 9mm CMMG Guard and his went down. I don't think he completed the match (he wasn't in my squad so didn't get to see him shoot). He just told me later his ejector spring died. He was running the 9mm Kynshot, 556 Tubb flat spring and A5 w/ a PSA Glock lower and RDIAS. I think he was running suppressed as well. I know he was running it for a while in this configuration so not sure how many rounds he put through it before it went down. |
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Quoted: I read back but don't see mention of the extractor spring wearing out as well as the ejector spring. Has your extractor spring lasted about as long as the ejector spring? After the pictures... |
| Do you have reason to think and out-of-the-box Guard setup will have issues with the spring if ran suppressed, semi-auto only? The whole reason I wanted to pick up a Guard setup is for suppressed usage, with the RDB setup being smoother than the blowback design. |
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Quoted:
I posted about just a few posts up....see my post above: Posted: 2/3/2019 5:51:28 PM EST After the pictures... re. The extractor spring now seems to be taking a beating. When I went to check it, the extractor pin had actually broken but it was still working. As 'backbencher' posted before, I agree that I don't think the extractor is needed for anything other than for manually extracting a live round. I am going test test firing the Guard w/ the no extractor next time to confirm. How did that turn out? |
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Seriously though guys, I think the extractor and bolt spring are non-issues for those that continue using the ejector in the bolt.
I think the ejector spring is the canary in the coal mine....when that starts to die, you are going to have problems. If it is dying in less than 30 rounds, you are slowing the gun down too much and need to put your buffer on a diet, adjust buffer spring, etc... However, nothing I've seen is going to kill that ejector spring that fast unless you are doing like me and modifying the geometry of the bolt lugs like I did on that 5.45x39 bolt. I suspect most of you will end up just sticking with the ejector in the bolt and play with various buffers/springs. As I've shown, this is still a great setup and I think very nice unsuppressed. Suppressed still nice but to me lags behind the MP5. I had to go to the fixed ejector to surpass the MP5 suppressed. (My OPINION of course....this is all subjective).... I'm using the Holosun optic on there with that small objective and my buddy that has a lot of MP5 trigger time and also a federal LE agent commented on how he never loses the sight picture on my setup during full auto and was quite impressed. That was basically my objective...not to lose the sight picture in full auto unsuppressed and suppressed. I'll still test firing the Guard w/ no extractor for my own knowledge/reference but again, I think it is a non-issue for everyone running the ejector in the bolt. |
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Quoted:
I'll still test firing the Guard w/ no extractor for my own knowledge/reference but again, I think it is a non-issue for everyone running the ejector in the bolt. |
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Did a side by side with my 'hybrid' Guard using the fixed ejector and the MP5K PDW.
(2) mags loaded to 10 rounds each. 1st mag fired at center mass then 2nd mag fired at head/neck area. 
https://www.youtube.com/watch?v=kIMlXOpFop0 I put the image below at the end of the video but it got cropped off so pasted it below. Got 18 hits on both. I suspect the two missing rounds were when I was going for the head/neck area. I think I had to compensate for the high cyclic rate more on the MP5K PDW why more rounds seem to be lower on the MP5 target. You can see in the video it is about 50 feet away. I have a friend that is a firearms instructor for a living and trains LE all the time, is an expert with the MP5 as well as other SMG's and has won the Knob Creek SMG match many times w/ the MP5. He has just about every SMG in his inventory, including the latest CZ Scorpions, MPX, B&T etc and he agrees that the MP5 is still the king when it comes to a closed bolt SMG. I look forward to letting a real expert do the same comparison. BTW, along w/ using the fixed ejector, my Guard was using the 9mm Kynshot, 300BLK Tubb flat spring, A5 buffer tube and no weight in the carrier. I only did this test once and would like to do it again suppressed. The Guard is considerably lighter than the MP5 and curious how things would play out with more mass at the end. The 556 Tubb flat spring may also be a little flatter but I think about 30RPM faster. Nice thing is that the Guard can be tweaked while the MP5 is what it is. Note the obvious that the MP5 has no BHO so manipulation of the charging handle is required. 
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Quoted:
Did a side by side with my 'hybrid' Guard using the fixed ejector and the MP5K PDW. (2) mags loaded to 10 rounds each. 1st mag fired at center mass then 2nd mag fired at head/neck area. https://i.ytimg.com/vi/kIMlXOpFop0/hqdefault.jpg?sqp=-oaymwEZCPYBEIoBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLAHpchiM3KtN4o07WKWTphsp7TKVA https://www.youtube.com/watch?v=kIMlXOpFop0 I put the image below at the end of the video but it got cropped off so pasted it below. Got 18 hits on both. I suspect the two missing rounds were when I was going for the head/neck area. I think I had to compensate for the high cyclic rate more on the MP5K PDW why more rounds seem to be lower on the MP5 target. You can see in the video it is about 50 feet away. I have a friend that is a firearms instructor for a living and trains LE all the time, is an expert with the MP5 as well as other SMG's and has won the Knob Creek SMG match many times w/ the MP5. He has just about every SMG in his inventory, including the latest CZ Scorpions, MPX, B&T etc and he agrees that the MP5 is still the king when it comes to a closed bolt SMG. I look forward to letting a real expert do the same comparison. BTW, along w/ using the fixed ejector, my Guard was using the 9mm Kynshot, 300BLK Tubb flat spring, A5 buffer tube and no weight in the carrier. I only did this test once and would like to do it again suppressed. The Guard is considerably lighter than the MP5 and curious how things would play out with more mass at the end. The 556 Tubb flat spring may also be a little flatter but I think about 30RPM faster. Nice thing is that the Guard can be tweaked while the MP5 is what it is. Note the obvious that the MP5 has no BHO so manipulation of the charging handle is required. http://c3junkie.com/wp-content/uploads/2019/02/Guard-vs-MP5KPDW-1024x805.jpg |
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Quoted: Looking forward to your suppressed test with their recommended carrier weight. If you've seen my previous post, I got it to run at 504 RPM SUPPRESSED with NO carrier weight. No point in adding weight with this configuration when using a fixed ejector. |
[ARCHIVED THREAD] - Full Auto CMMG Guard Tuning (Page 3 of 4)
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