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[ARCHIVED THREAD] - Thoughts on the CMMG Guard? (Page 13 of 25)
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Rifle (longest tube) - smoothest, slowest RoF but had some reliability issues A5 - (Med tube) 2nd in terms of smoothest and RoF but reliable Carbine (short tube) - worst in smoothest and fastest RoF but reliable UICW (even shorter tube) - ? |
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Quoted: That's a good summary. The shorter buffer in the UCIW cancels the one inch difference in tube length so I may get lucky and have an acceptable result. Appears from all the previous testing I can't expect better than carbine level performance as above. I did test an H2 (4.5oz) and even with a custom tungsten 5.1 oz carrier weight it was too fast for me to get singles. I did further testing on my site with a 9mm Colt bolt weight (3.5oz) as well. I am currently not using any carrier weight now but you may want to consider getting the tuning kit if you are hard pressed to use that UCIW stock. https://www.cmmginc.com/product/action-tuning-kit-mkg/ 
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You say the 308 hydraulic buffer you are considering is 3.7oz. I did test an H2 (4.5oz) and even with a custom tungsten 5.1 oz carrier weight it was too fast for me to get singles. I did further testing on my site with a 9mm Colt bolt weight (3.5oz) as well. I am currently not using any carrier weight now but you may want to consider getting the tuning kit if you are hard pressed to use that UCIW stock. https://www.cmmginc.com/product/action-tuning-kit-mkg/ https://www.cmmginc.com/wp-content/uploads/2017/04/45AFF17.jpg |
| reliability is up by the way using the tubbs 300 blackout/pistol spring (same spring with less coils). I don't have tons of rounds on it, but it seems to be running well. The weaker spring on the 9mm seems plenty good enough though. Need to get out and run them on the timer. |
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reliability is up by the way using the tubbs 300 blackout/pistol spring (same spring with less coils). I don't have tons of rounds on it, but it seems to be running well. The weaker spring on the 9mm seems plenty good enough though. Need to get out and run them on the timer. Are you still using the 9mm Blitzkrieg with no weight? |
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Quoted: That's a good summary. The shorter buffer in the UCIW cancels the one inch difference in tube length so I may get lucky and have an acceptable result. Appears from all the previous testing I can't expect better than carbine level performance as above. I'll swap the shorty Kynshot buffer for a 5.5 oz. RB5005 (AR10), 3.25". A half oz. lighter than the Blitzkrieg. If it doesn't feel right I'll get an A5 tube and follow amphibians' formula. |
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I need to try that again...I think I was having ejection problems last time I tried that spring. The Guard system is hard on the ejector spring. CMMG technical support told me that the ejection springs for the early 9mm Guards were using standard 556 ejector springs while the 45 Guard uses a shorter spring but is actually stronger and they now use the 45 ejector spring in the 9mm and 45 now. I'm waiting on some replacements from them now. Are you still using the 9mm Blitzkrieg with no weight? |
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CMMG just sent me new ejector and buffer springs. The ejector spring was longer than the one I took out and took more force to compress. The new buffer spring is now a standard .556 carbine spring. I should be shooting a match tomorrow and will find out if this fixes my occasional failures to eject. Quoted:
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I need to try that again...I think I was having ejection problems last time I tried that spring. The Guard system is hard on the ejector spring. CMMG technical support told me that the ejection springs for the early 9mm Guards were using standard 556 ejector springs while the 45 Guard uses a shorter spring but is actually stronger and they now use the 45 ejector spring in the 9mm and 45 now. I'm waiting on some replacements from them now. Are you still using the 9mm Blitzkrieg with no weight? Just as they told me the ejector springs are actually shorter but stronger than a 556 ejector spring. New Guard on the left and the Sprinco (tacticalsprings.com) on the right. Note the Sprinco's are the same length as other 556 ejector springs...just using these for reference. 
Guard Ejector spring: 
Sprinco ejector spring: 
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Interesting. I did not measure them, just laid them side by side, original and new. Wonder why I had no problems for 6,000 plus rounds with the original. Maybe the original fatigued. The original had a sight bend to it when I took it out. The new spring definitely took more effort to compress when replacing.
Looking forward to the match today. |
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I also bought a CMMG Guard kit that arrives tomorrow. I bought it with the Action Tuning Kit that CMMG sells for the Guard, which is essentially a set of different weights you can add to the carrier. I wonder how the tuning will go with that. I currently use a Tubb flatwire carbine spring and and H buffer on my SBR lower for 5.56. I guess I could start with the heaviest weight for the carrier and go down until I get reliable cycling. I always like to go the heaviest on the buffer/recoil system that reliably cycles on blowbacks, to me it "feels" the best. I tested with a custom tungsten bolt weight that weighs 5.1 oz and with an H2 buffer it was too fast. This was also with a 556 Tubb Flat wire spring. So I would think that an H buffer and Tubb Flatwire would function just fine. The heaviest CMMG bolt weight is 3.5oz (made of steel). |
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As mentioned here: http://c3junkie.com/?page_id=538 I tested with a custom tungsten bolt weight that weighs 5.1 oz and with an H2 buffer it was too fast. This was also with a 556 Tubb Flat wire spring. So I would think that an H buffer and Tubb Flatwire would function just fine. The heaviest CMMG bolt weight is 3.5oz (made of steel). I'm still a little confused. You said you used a 5.1oz custom carrier weight and an H2 buffer and it was still too fast, but the CMMG 3.5oz carrier weight and an H buffer should be fine? Wouldn't it be even faster with the lighter weight and H buffer? Or were you just talking about reliability and not ROF? I'm obviously semi-auto, but I still like to keep the action slow for best "felt" recoil. Thanks for clarifying. |
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Quoted: Thank you for the reply and for bringing the question over here. I'm still a little confused. You said you used a 5.1oz custom carrier weight and an H2 buffer and it was still too fast, but the CMMG 3.5oz carrier weight and an H buffer should be fine? Wouldn't it be even faster with the lighter weight and H buffer? Or were you just talking about reliability and not ROF? I'm obviously semi-auto, but I still like to keep the action slow for best "felt" recoil. Thanks for clarifying. I'm thinking you could use that 556 Tubb flat wire spring and the buffer of your choosing to work with both the Guard and your other 556 uppers so you don't have to change anything in your lower. |
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Yes its the SBR Banshee lower. It fits other CMMG lowers fine Is it too tight or is the shelf is not low enough? |
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I don’t have it handy but it’s this area, and specifically that rear corner that juts out too much |
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Finally got out to the range today with my Banshee upper:
Kynshot AR10 Buffer/Tubbs Flat Wire AR15 spring, Magpul CTR stock (7" tube), Spike's Compressor Cal-Multi lower, CMMG Banshee 9mm upper. Fired from a bench resting on ranger plates, Pmag M3's/Endomag inserts. Kaw XL (the big fat one) Linear Comp. (It was unexpectedly efficient.) I was very happy with the Banshee and it felt great with the hydraulic buffer and flat wire spring. It is a lot quieter than the round spring. Thanks Amphibian for paving the road with your testing. Could you comment on the following? For my 5.56 upper I had to put back in the Spike's carbine spring, I think the Tubbs was too strong and was short stroking. What do you think? Snip coils? FYI: The sweetest combo from testing today: My Spike's .300 BLK Compressor upper with subsonic ammo and the Kynshot AR10 buffer. It slowed down rate of fire nicely and was so smooth it startled me. Like someone was lightly nudging my shoulder, no sudden jolt, more of a push. VERY quiet. |
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Yeah I guess I'll have to do that. It just bugs me that they changed the lower for no reason. And they told me it was RDIAS compatable when I was considering buying it.. Well, it isn't if you and me have to machine it to fit. |
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Finally got out to the range today with my Banshee upper: Kynshot AR10 Buffer/Tubbs Flat Wire AR15 spring, Magpul CTR stock (7" tube), Spike's Compressor Cal-Multi lower, CMMG Banshee 9mm upper. Fired from a bench resting on ranger plates, Pmag M3's/Endomag inserts. Kaw XL (the big fat one) Linear Comp. (It was unexpectedly efficient.) I was very happy with the Banshee and it felt great with the hydraulic buffer and flat wire spring. It is a lot quieter than the round spring. Thanks Amphibian for paving the road with your testing. Could you comment on the following? For my 5.56 upper I had to put back in the Spike's carbine spring, I think the Tubbs was too strong and was short stroking. What do you think? Snip coils? FYI: The sweetest combo from testing today: My Spike's .300 BLK Compressor upper with subsonic ammo and the Kynshot AR10 buffer. It slowed down rate of fire nicely and was so smooth it startled me. Like someone was lightly nudging my shoulder, no sudden jolt, more of a push. VERY quiet. You shouldn't be using that buffer with the Guard or 556 BCG with a 7" carbine buffer tube....you are risking damaging your lower doing that....unless you put a spacer in the buffer tube to prevent it from bottoming out. You should be using a 3.5" carbine buffer in a carbine length tube. I'm personally not a fan of cutting coils. |
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I thought you were planning on using that 2.5" AR10 Kynshot buffer in that shorter LWRC UICW tube and then changed your mind? You shouldn't be using that buffer with the Guard or 556 BCG with a 7" carbine buffer tube....you are risking damaging your lower doing that....unless you put a spacer in the buffer tube to prevent it from bottoming out. You should be using a 3.5" carbine buffer in a carbine length tube. I'm personally not a fan of cutting coils. My Compressor came with a 3.25" Spikes T3 buffer. The Kynshot 5005 is the same length compressed. How can it damage the receiver? EDIT: Oh I get it you thought I still had the 2.5" Kynshot buffer, the 5004. I swapped it for the 5005 which is 3.25" compressed. |
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I tried the 2.5" but it was too short even compressed for the tube. It worked but just barely. I swapped back to the Magpul CTR stock. My Compressor came with a 3.25" Spikes T3 buffer. The Kynshot 5005 is the same length compressed. How can it damage the receiver? EDIT: Oh I get it you thought I still had the 2.5" Kynshot buffer, the 5004. I swapped it for the 5005 which is 3.25" compressed. |
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5005 is also a 308 Kynshot buffer...I have no experience with any of the 308 Kynshot buffers btw I found out the Spike's Compressor spring is a standard 17-7 Polished Stainless spring. Worked like a dream with the .300 BLK upper. |
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Guard system, Endomags, A5 extension. 110rds of Magtech. 0 issues (aside from being unable to lock in a full mag on a closed bolt).
Video |
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Guard system, Endomags, A5 extension. 110rds of Magtech. 0 issues (aside from being unable to lock in a full mag on a closed bolt). Video |
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I had a "premium" trigger on hand and I'm pretty particular about which handguard I like, so I built a guard from the 16" barrel/bolt kit, cmmg mkgs upper, and the mkgs lower.
Took it out today while the weather was ok. It ran like a clock for 200-250 rounds until the weather started raining and it got below freezing. I started having issues with the trigger not resetting properly. Certainly not the guard's fault though. While it was working I shot it back to back with a couple other blowback PCCs. I wouldn't say the recoil was significantly less than the blowback PCCs, the recoil was very similar. I did notice there was less movement when the bolt was moving back forward and clambering the next round so the overall impulse was smoother and a bit less jarring. I was running the lightest weight out of the tuning kit. I ran it suppressed and unsuppressed with 147 grain and 115 grain ammo. I didnt notice a significant difference in recoil impulse across ammo types or with/without a suppressor |
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I had a "premium" trigger on hand and I'm pretty particular about which handguard I like, so I built a guard from the 16" barrel/bolt kit, cmmg mkgs upper, and the mkgs lower. Took it out today while the weather was ok. It ran like a clock for 200-250 rounds until the weather started raining and it got below freezing. I started having issues with the trigger not resetting properly. Certainly not the guard's fault though. While it was working I shot it back to back with a couple other blowback PCCs. I wouldn't say the recoil was significantly less than the blowback PCCs, the recoil was very similar. I did notice there was less movement when the bolt was moving back forward and clambering the next round so the overall impulse was smoother and a bit less jarring. I was running the lightest weight out of the tuning kit. I ran it suppressed and unsuppressed with 147 grain and 115 grain ammo. I didnt notice a significant difference in recoil impulse across ammo types or with/without a suppressor |
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Quoted: Sounds like you might need a bit of tuning, either carrier weights or buffer weights and maybe spring rate I should have clarified that the gun was cycling fine but when I would follow through the trigger pull and not let it up until after the gun fully cycled the trigger wouldn't reset when I finally did let pressure off the trigger. I had to kind of jiggle the trigger to get it to reset. The bolt carrier was definitely going back far enough to cycle the action and reset the trigger (last round volt hold open was working fine as well). I could reproduce the issues when holding the trigger in and cycling the action with the charging handle so I was pretty convinced it was just the trigger and not the action of the Guard. Love the guard so far. Looking forward to shooting it in pcc in some local uspsa this winter |
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I was thinking the trigger issue wasn't related to the Guard, since it was the first time shooting that particular trigger I kinda figured it was an issue with that trigger. I should have clarified that the gun was cycling fine but when I would follow through the trigger pull and not let it up until after the gun fully cycled the trigger wouldn't reset when I finally did let pressure off the trigger. I had to kind of jiggle the trigger to get it to reset. The bolt carrier was definitely going back far enough to cycle the action and reset the trigger (last round volt hold open was working fine as well). I could reproduce the issues when holding the trigger in and cycling the action with the charging handle so I was pretty convinced it was just the trigger and not the action of the Guard. Love the guard so far. Looking forward to shooting it in pcc in some local uspsa this winter Quoted:
Quoted: Sounds like you might need a bit of tuning, either carrier weights or buffer weights and maybe spring rate I should have clarified that the gun was cycling fine but when I would follow through the trigger pull and not let it up until after the gun fully cycled the trigger wouldn't reset when I finally did let pressure off the trigger. I had to kind of jiggle the trigger to get it to reset. The bolt carrier was definitely going back far enough to cycle the action and reset the trigger (last round volt hold open was working fine as well). I could reproduce the issues when holding the trigger in and cycling the action with the charging handle so I was pretty convinced it was just the trigger and not the action of the Guard. Love the guard so far. Looking forward to shooting it in pcc in some local uspsa this winter Isnt that pretty much the point of the RDB setup? |
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Nice. Curious, did you get it direct form CMMG or elsewhere? Quoted:
Nice. Curious, did you get it direct form CMMG or elsewhere? Quoted:
what handgaurd you going to replace it with? CMT? |
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I wonder if the issue with ejector spring fatigue is being caused by the case halfway ejecting behind the locking lugs in the barrel extension recess. With rifle calibers the case is long so the ejector doesn't pivot the case till it comes out of the barrel extension. With a short case like the .45 and 9mm the ejector pivots the case into the barrel extension behind the lugs and then the lugs push the case back (and compress the ejector spring again) and then the case pivots out and ejects after it clears the locking lugs. So for every ejection event the ejector spring operates twice. I would think that would shorten the life of the spring by at least half. Maybe more than half on a full auto because you have the ejector spring compressing at twice the cyclic rate it normally would which is going to heat it up faster. On DI pistol caliber builds they sometimes put a guide pin in the false lug recess so the case doesn't pivot till it's fully clear of the lugs (on those it's done because they have so little operating energy that they can't afford to waste any compressing the ejector twice, but thinking on it now it also inadvertently benefits the life of the ejector spring). I don't see anything like this on the Guard RDB system. Am I incorrect on this? I don't have a guard in my hands to look at right now, but from what photos I have seen of the barrel extension recess I don't see any ejection guide in there. I have a 9mm guard barrel kit on order right now, I guess I will get to see firsthand when it arrives. |
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Look what I got for Black Friday.  . Now I need to replace the handguard and modify my QC10 glock lower.Does anyone know who else carries the 8" Guard upper? I've been looking, but either my Google-Fu is weak, or they only have them at CMMG's site. |
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I wonder if the issue with ejector spring fatigue is being caused by the case halfway ejecting behind the locking lugs in the barrel extension recess. With rifle calibers the case is long so the ejector doesn't pivot the case till it comes out of the barrel extension. With a short case like the .45 and 9mm the ejector pivots the case into the barrel extension behind the lugs and then the lugs push the case back (and compress the ejector spring again) and then the case pivots out and ejects after it clears the locking lugs. So for every ejection event the ejector spring operates twice. I would think that would shorten the life of the spring by at least half. Maybe more than half on a full auto because you have the ejector spring compressing at twice the cyclic rate it normally would which is going to heat it up faster. On DI pistol caliber builds they sometimes put a guide pin in the false lug recess so the case doesn't pivot till it's fully clear of the lugs (on those it's done because they have so little operating energy that they can't afford to waste any compressing the ejector twice, but thinking on it now it also inadvertently benefits the life of the ejector spring). I don't see anything like this on the Guard RDB system. Am I incorrect on this? I don't have a guard in my hands to look at right now, but from what photos I have seen of the barrel extension recess I don't see any ejection guide in there. I have a 9mm guard barrel kit on order right now, I guess I will get to see firsthand when it arrives. No such pin with the Guard. I'll have to look closer to see if adding one would be possible. The extractor doesn't have an angled lug like the rest so maybe? |
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Do you mind if I ask how much it was? I have been looking for the 8" upper, and didn't see that CMMG had a Black Friday sale. Does anyone know who else carries the 8" Guard upper? I've been looking, but either my Google-Fu is weak, or they only have them at CMMG's site. |
| If you are going for the 8 inch setup you might be better off getting the barrel and bolt combo for around $300 (opticsplanet w/10% off) and getting a 458 socom upper from Aero. DIY and save a few hundred. (per Amphibian the 458 uppers are opened/clearanced like the CMMG's). |
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If you are going for the 8 inch setup you might be better off getting the barrel and bolt combo for around $300 (opticsplanet w/10% off) and getting a 458 socom upper from Aero. DIY and save a few hundred. (per Amphibian the 458 uppers are opened/clearanced like the CMMG's). |
[ARCHIVED THREAD] - Thoughts on the CMMG Guard? (Page 13 of 25)
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