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Posted: 1/14/2018 3:10:27 AM EDT
[#1]
CMMG, put me down as another vote for a slow fire bolt.
Also, wouldn’t a slow fire bolt also help out with suppressed fire? I am guessing it would keep the bolt locked longer, which would eliminate some of the need for extra tuning weight, and lower the amount of blowback. (Yes, I know you said it isn’t an issue, but less is always better). |
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Posted: 1/16/2018 12:01:08 AM EDT
[#2]
Why is their 9mm threaded 1/2 x 36 arghh!
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Posted: 1/16/2018 4:30:39 PM EDT
[#3]
Quote HistoryQuoted:
Why is their 9mm threaded 1/2 x 36 arghh! |
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Posted: 1/16/2018 4:51:54 PM EDT
[#4]
Quote HistoryQuoted:
Because that is the standard for 9 mm sub guns. Avoids putting the wrong item on your barrel. Quote HistoryQuoted:
Quoted:
Why is their 9mm threaded 1/2 x 36 arghh! |
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Posted: 1/16/2018 5:29:23 PM EDT
[#5]
Quote HistoryQuoted:
Dr_evil, how many rounds did you run with your test? Trying to gauge the reliability you are getting. Also, how much fitting did you have to do with the RDIAS? Any timing needing to be done as well? So I didn't get a chance to do extensive testing, and since I self dremeled my way into getting my RDIAS in there....I may have some minor timing issues as well. Single shots were very very easy. I didn't get a chance to do any full dumps. More testing is required, but it would appear that the A5 system is much better for competition than the Carbine system (for Subgun). I haven't tried the rifles system yet so that's obviously possible as well. |
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Posted: 1/16/2018 5:34:40 PM EDT
[#6]
Quote HistoryQuoted:
It has been in the past. Most manufacturers have changed to 1/2 x 28 in the last couple years. True story. Quote HistoryQuoted:
Quoted:
Quoted:
Why is their 9mm threaded 1/2 x 36 arghh! Some 9mm barrels have used 1/2 x 32 or 9/16 x 24. |
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Posted: 1/17/2018 9:45:44 PM EDT
[#7]
I took my new build from the CMMG Guard BCG/barrel/lower for sighting in and testing of magazines, etc. I was getting about 1 in 15 failing to eject. CMMG posted if you don’t use their upper, you may have to clearance the ejection port. I didn’t think much of this as Colt SMG uses a standard ejection port that works well with 9 mm. Now I feel differently.
In comparing my factory Guard and my AR15 upper, there is quite a difference between the Guard ejection port and an AR 15 ejection port. The guard ejection port is clearanced on the lower edge all the way to the bolt bearing surface. The top edge is clearanced on the first half of the port to the extent it takes out about half of the upper bolt bearing surface. The ends of the Guard port are also more squared off instead of round, probably due to the end mill size. I feel CMMG did this for reliability and maybe to accommodate different types of ammo. Also, who knows the differences in the shell ejection between a Colt SMG style ejector and an AR15 type of ejector. I had my mill set up for milling lines in my last linear comp. Should not be hard to do an exact reproduction of the Guard upper. If this stops the ejection problem, it would make sense to use the Guard upper with the BCG/barrel/lower for a custom build. (If you don’t have a mill with a rotary table.  )
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Posted: 1/17/2018 10:05:25 PM EDT
[#8]
Next steps:
ALG M-Lok handguard cut to 5" Barrel cut to 5.75" and threaded 5/8x24. Experimentation with suppressors, ammo types and reciprocating weights. Sell old blowback barrel bolt and buffer. So much fun! |
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Posted: 1/17/2018 10:08:38 PM EDT
[#9]
Quote HistoryQuoted:
I took my new build from the CMMG Guard BCG/barrel/lower for sighting in and testing of magazines, etc. I was getting about 1 in 15 failing to eject. CMMG posted if you don’t use their upper, you may have to clearance the ejection port. I didn’t think much of this as Colt SMG uses a standard ejection port that works well with 9 mm. Now I feel differently. In comparing my factory Guard and my AR15 upper, there is quite a difference between the Guard ejection port and an AR 15 ejection port. The guard ejection port is clearanced on the lower edge all the way to the bolt bearing surface. The top edge is clearanced on the first half of the port to the extent it takes out about half of the upper bolt bearing surface. The ends of the Guard port are also more squared off instead of round, probably due to the end mill size. I feel CMMG did this for reliability and maybe to accommodate different types of ammo. Also, who knows the differences in the shell ejection between a Colt SMG style ejector and an AR15 type of ejector. I had my mill set up for milling lines in my last linear comp. Should not be hard to do an exact reproduction of the Guard upper. If this stops the ejection problem, it would make sense to use the Guard upper with the BCG/barrel/lower for a custom build. (If you don’t have a mill with a rotary table. )My Franken-Guard is working fine with a standard upper. I think the modified upper is more needed for the Guard 45. |
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Posted: 1/18/2018 12:03:22 AM EDT
[#10]
Quote HistoryQuoted: Check out the Anderson 458 SOCOM upper receiver. My Franken-Guard is working fine with a standard upper. I think the modified upper is more needed for the Guard 45. |
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Posted: 1/18/2018 2:08:16 PM EDT
[#11]
Testing is leading to more testing...
Brought a mixture of range ammo with me last night. I knew some of it might be a little weaker/stronger, but no idea what a difference it would make. The A5 system has been excellent in both semi and full auto. Its buttery smooth with weak ammo (Blazer Brass, others). The Blazer Brass worked well on the A5-H0, A5-H1, A5-H2 buffers (had one non lock back after full mag dump with A5-H2). The system definitely choked on the A5-H3 with Blazer Brass. This was also with the 3.5oz tuning weight installed. Hotter ammo cycled harder/harsher and worked all the way up to the A5-H4 buffer, but seems it could use even more weight in the A5 system. I have a tunable buffer from Heavy Buffers dot com....but I checked last night and it looks like i need to buy an additional tungsten kit to get the weight higher. May try some custom spring set ups tonight first. Then will purchase the kit and also try the rifle system. Should be noted that you can get singles with all of these set ups....easier with the weak ammo and less consistently with stronger ammo. |
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Posted: 1/20/2018 11:52:20 PM EDT
[#12]
I want a high pressure/low cyclic rate bolt to test.
Have any available, CMMG? |
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Posted: 1/20/2018 11:56:51 PM EDT
[#13]
Quote HistoryQuoted:
I want a high pressure/low cyclic rate bolt to test. Have any available, CMMG? |
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Posted: 1/21/2018 11:34:19 AM EDT
[#14]
I'll put in a word for the FN 5.7x28mm round. A mag block for the pistol magazine w/ a delayed blowback upper would make a pretty sweet companion carbine. Though .357 SIG in Glock mags would probably get one to the same place.
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Posted: 1/21/2018 3:29:30 PM EDT
[#15]
Quote HistoryQuoted:
I'll put in a word for the FN 5.7x28mm round. A mag block for the pistol magazine w/ a delayed blowback upper would make a pretty sweet companion carbine. Though .357 SIG in Glock mags would probably get one to the same place.
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Posted: 1/21/2018 5:16:02 PM EDT
[#16]
After reading about those who've been playing around with different weight configurations, it got me thinking about my franken-Guard set up and some questions came up.
Even though the Guard is a 'delayed' blowback system, it's blowback none the less which means it still requires a certain amount of mass to prevent the bolt from opening too soon correct? Basically the same as straight blowback but since it has a delay it doesn't require as much mass? I ask because my set up uses a cut down Guard bolt carrier and Rock River PDS recoil system: 
Together it weighs 11.7oz. By comparison, the stock Guard BCG with standard carbine buffer is 14.8oz. I've only been shooting 9mm so far (semi-auto, commercial 115g-158g, suppressed and un-suppressed). After reading about ROF's, different weights, etc I'm concerned this lighter setup might lead to out-of-battery conditions that occur with straight blowback guns using too light of a bolt/buffer. So what say ye? 11.7oz too light for safe operation of the Guard system? Am I asking for trouble? |
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Posted: 1/21/2018 5:44:35 PM EDT
[#17]
Quote HistoryQuoted:
So what say ye? 11.7oz too light for safe operation of the Guard system? Am I asking for trouble? |
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Posted: 1/21/2018 10:41:35 PM EDT
[#18]
Yep, was considering that as well. I chopped & re-threaded the barrel so it's around 8" now. I'd like to go shorter but the design of the RRA upper doesn't really allow for it.
I also been routinely inspecting the brass and don't see any obvious OOB signs like bulged cases. Also, assuming same barrel lengths, bullet mass has the greatest affect on required weight of the bolt/buffer, no? That's why a straight blowback, say, 45ACP uses 8-10+oz of weight compared ~5.5oz for 9mm? (I want to try this with 45 next but don't want to blow my face off) |
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Posted: 1/21/2018 10:49:59 PM EDT
[#19]
Quote HistoryQuoted:
Also, assuming same barrel lengths, bullet mass has the greatest affect on required weight of the bolt/buffer, no? That's why a straight blowback, say, 45ACP uses 8-10+oz of weight compared ~5.5oz for 9mm? (I want to try this with 45 next but don't want to blow my face off) Comparing across calibers, I assume the difference (bolt+buffer requirement) has to do with gas volume and maybe case diameter. |
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Posted: 1/21/2018 11:44:12 PM EDT
[#20]
Quote HistoryQuoted:
I don't think so, at least not within the same caliber. I ran the numbers for 115gr and 124gr for my setup, and the power factor was virtually identical for both. As the weight goes up, the velocity goes down. Comparing across calibers, I assume the difference (bolt+buffer requirement) has to do with gas volume and maybe case diameter. |
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Posted: 1/22/2018 12:51:52 PM EDT
[#21]
It will be interesting to see how a 5.75" barrel with can affects optimal mass.
I'd like to run it with a UCIW or VERT setup. |
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Posted: 1/22/2018 1:27:18 PM EDT
[#22]
Quote HistoryQuoted:
It will be interesting to see how a 5.75" barrel with can affects optimal mass. I'd like to run it with a UCIW or VERT setup. |
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Posted: 1/22/2018 2:27:29 PM EDT
[#23]
Quote HistoryQuoted:
After reading about those who've been playing around with different weight configurations, it got me thinking about my franken-Guard set up and some questions came up. Even though the Guard is a 'delayed' blowback system, it's blowback none the less which means it still requires a certain amount of mass to prevent the bolt from opening too soon correct? Basically the same as straight blowback but since it has a delay it doesn't require as much mass? I ask because my set up uses a cut down Guard bolt carrier and Rock River PDS recoil system: https://i.imgur.com/h98Y7Eo.jpg Together it weighs 11.7oz. By comparison, the stock Guard BCG with standard carbine buffer is 14.8oz. I've only been shooting 9mm so far (semi-auto, commercial 115g-158g, suppressed and un-suppressed). After reading about ROF's, different weights, etc I'm concerned this lighter setup might lead to out-of-battery conditions that occur with straight blowback guns using too light of a bolt/buffer. So what say ye? 11.7oz too light for safe operation of the Guard system? Am I asking for trouble? I don't know that you'll see much issue with 9mm, as long as you've got a poly bolt buffer to absorb the impact. .45 or 10mm might get a little iffy. |
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Posted: 1/22/2018 4:50:58 PM EDT
[#24]
Quote HistoryQuoted:
This is nearly identical to what I had considered doing with my next bufferless upper for my .45 SBR. I don't know that you'll see much issue with 9mm, as long as you've got a poly bolt buffer to absorb the impact. .45 or 10mm might get a little iffy.  Man, I want to try 45. At least once. 10mm would be a long way off but most likely my next PCC project.
The stock PDS "buffer" is nothing more than a plastic disk (perhaps Delrin), maybe 1/8" thick. I put a thick rubber washer behind it to help absorb more of the shock. I'd love to make something a little more substatial like the one in the MPX (pic from PMM): 
Matter of fact, the MPX buffer looks like it would bolt right into my gun. Anyone happen to know the dimensions of it? Length & OD? |
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Posted: 1/22/2018 11:37:10 PM EDT
[#25]
I can measure at work tomorrow.
Be mindful of stroke length. |
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Posted: 1/23/2018 12:46:07 AM EDT
[#26]
Quote HistoryQuoted:
I can measure at work tomorrow. Be mindful of stroke length. I'd definitely need to shorten the carrier more if I used an MPX buffer with the PDS lower (The stock buffer sits almost flush with the receiver): 
I have a few other standard lowers I'm also experimenting with. Plan would be to use a screw-in type adapter like this: 
That would allow use of a longer buffer like the MPX. Now whether continual cycling would eventually damage the receiver threads? Remains to be seen. |
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Posted: 1/23/2018 11:39:50 PM EDT
[#27]
I skimmed the thread and saw problems with ejection because of the widened Guard ejection port. I apologize if it's been asked already but does anyone know if the Guard 9mm bolt carrier and barrel will feed and function in a standard Colt-pattern AR upper and lower? Their website says "may."
https://www.cmmginc.com/product/barrel-and-bcg-kit-8-4140cm-sbn-9mm |
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Posted: 1/24/2018 12:15:54 AM EDT
[#28]
A few of us have gotten it to work with Colt-style setups: 9mm-Guard-Barrel-and-BCG-working-with-Colt-mags
It's not plug & play however; some modifications need to be done to the magazines and/or feed ramp. Depends on your exact setup (Metalform vs Uzi vs ASC mags, mag block vs dedicated lower, etc) |
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Posted: 1/29/2018 2:07:40 AM EDT
[#29]
Quote HistoryQuoted:
I can measure at work tomorrow. 
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Posted: 1/29/2018 9:07:39 AM EDT
[#30]
I looked and don't have an MPX.
Will try to get my hands on one. |
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Posted: 1/29/2018 1:11:12 PM EDT
[#31]
Quote HistoryQuoted:
I took my new build from the CMMG Guard BCG/barrel/lower for sighting in and testing of magazines, etc. I was getting about 1 in 15 failing to eject. CMMG posted if you don’t use their upper, you may have to clearance the ejection port... So, if you are having any ejection problems with your Guard barrel/BCG build, I highly recommend clearancing the ejection port. |
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Posted: 1/29/2018 1:21:19 PM EDT
[#32]
Quote HistoryQuoted:
I looked and don't have an MPX. Will try to get my hands on one. |
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Posted: 1/29/2018 1:25:44 PM EDT
[#33]
Quote HistoryQuoted: Finished milling my upper to open up the ejection port. I milled the top front half 0.038" and the entire length of the bottom 0.110". I ran all my Glock mags from fully loaded and not one failure to eject. Today I ran a steel match and not one failure to eject. 400 rounds total. So, if you are having any ejection problems with your Guard barrel/BCG build, I highly recommend clearancing the ejection port. |
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Posted: 1/29/2018 9:07:09 PM EDT
[#34]
Quote HistoryQuoted: This was with 9mm correct? |
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Posted: 1/29/2018 10:04:59 PM EDT
[#35]
Quote HistoryQuoted: Yes, 9mm. I figure that with the Guard type of ejector, you need a little bit more opening, else why would they do it. CMMG mentions that you may have to clearance a non-CMMG upper. |
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Posted: 1/29/2018 10:22:02 PM EDT
[#36]
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Posted: 1/29/2018 10:22:49 PM EDT
[#37]
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Posted: 1/29/2018 11:36:06 PM EDT
[#38]
 CMMG GUARD 9mm 5.75" Suppressed, Full Auto, Subsonic  CMMG GUARD 9mm 5.75" Suppressed, Full Auto |
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Posted: 1/30/2018 12:12:13 AM EDT
[#39]
Thanks, Backbencher!
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Posted: 1/30/2018 1:34:55 AM EDT
[#40]
How does the guard compare to the MP5?
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Posted: 1/30/2018 2:21:09 AM EDT
[#41]
Quote HistoryQuoted:
YouTube Link 1 -Any FTF/FTE issues come up in various configurations? (suppressed vs unsuppressed, semi vs auto, super vs subsonic, etc) -Which can were you using? |
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Posted: 1/30/2018 11:34:08 AM EDT
[#42]
-After chopping the barrel, which buffer did you end up using? Any tuning weights?
H2 buffer, no tuning weights -Any FTF/FTE issues come up in various configurations? (suppressed vs unsuppressed, semi vs auto, super vs subsonic, etc) Had one FTF with the subs, which are 135gr and below 125 power factor. -Which can were you using? Griffin Armament Revolution 9mm. |
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Posted: 1/30/2018 11:54:49 AM EDT
[#43]
Quote HistoryQuoted: How does the guard compare to the MP5? One has proprietary expensive magazines, drums available up to 100 rnds; one has multiple drums available for it, and hobbyist work being done to adapt it to Uzi/Colt magazines. One has last round bolt hold open, one does not. One is easily changeable to different calibers with pre-existing magazines, one is not. One is still being developed by the original manufacturer; one is not. One is easily convertible to other operating systems and calibers; one is not. |
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Posted: 1/31/2018 7:18:03 PM EDT
[#44]
Quote HistoryQuoted:
A few of us have gotten it to work with Colt-style setups: 9mm-Guard-Barrel-and-BCG-working-with-Colt-mags It's not plug & play however; some modifications need to be done to the magazines and/or feed ramp. Depends on your exact setup (Metalform vs Uzi vs ASC mags, mag block vs dedicated lower, etc) |
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Posted: 2/1/2018 6:47:56 PM EDT
[#45]
Rifle buffer system
Kynshot buffer, and flat wire spring (Tubbs) = money Best, smoothest, slowest full auto cyclic rate across a wide range of ammo. A standard rifle buffer and standard spring aren't that far off, but the difference is more notable with +P/Hot ammo The extra heavy buffer by heavybuffers.com (rifle) is too heavy for reliable full auto fire (unless you run exclusively +P ammo), but works in semi In my rifle testing I used the 1 oz. tuning weight and the Law folding stock adapter (to make using a rifle system more pack-able/convenient. The small insert at the back of the carrier is a little over 2oz so along with the 1oz tuning weight this approximates the 3.5 oz weight (with out a law folding stock adapter). I tried the regular power spring, extra power spring (from heavy buffers.com) and the flatwire along with the regular, kynshot and extra heavy heavybuffers.com rifle buffer. I testing weak reloaded ammo, hotter magtec and Prime ammo (124 grain) along with speer gold dot 124 +P, gold dot 124, gold dot 147, magtech 115 +P+ The A5 system Its a close second behind the rifle system and you can get very smooth/slow full auto fire with weaker ammo, singles are still very easy with hotter ammo but full auto is not as smooth. You can play with which buffer but its mostly based on the ammo you're using. |
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Posted: 2/1/2018 6:48:39 PM EDT
[#46]
Carbine system
I could not get full auto to be smooth/slow. Flat wire spring with Kynshot buffer was the best I could do (with the 3.5 oz weight installed). I could reliably get singles out of this system, but full auto is much harsher than the other systems by far. Semi auto - I could actually get an MGI buffer or almost any buffer to work (in semi only), But not if you combine it with a heavier spring This new Guard 9mm/rifle length buffer/RDIAS set up will be my new competition gun :) I will eventually do some testing on the .45 - but its sounds like it already runs pretty slow/smooth with no modification in full auto |
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Posted: 2/1/2018 7:26:36 PM EDT
[#47]
Related Question...has anyone tried to get the JP captured spring system to run in full auto?
I was a little frustrated as I purchased their system, only to find that its basically a carbine length system only (with spacers) and a disclaimer that says it wasn't intended for full auto use (may not function properly). |
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Posted: 2/2/2018 10:42:45 PM EDT
[#48]
Quote HistoryQuoted: It has been in the past. Most manufacturers have changed to 1/2 x 28 in the last couple years. True story. Quote HistoryQuoted: It has been in the past. Most manufacturers have changed to 1/2 x 28 in the last couple years. True story. Quoted:
I took my new build from the CMMG Guard BCG/barrel/lower for sighting in and testing of magazines, etc. I was getting about 1 in 15 failing to eject. CMMG posted if you don’t use their upper, you may have to clearance the ejection port. I didn’t think much of this as Colt SMG uses a standard ejection port that works well with 9 mm. Now I feel differently. In comparing my factory Guard and my AR15 upper, there is quite a difference between the Guard ejection port and an AR 15 ejection port. The guard ejection port is clearanced on the lower edge all the way to the bolt bearing surface. The top edge is clearanced on the first half of the port to the extent it takes out about half of the upper bolt bearing surface. The ends of the Guard port are also more squared off instead of round, probably due to the end mill size. I feel CMMG did this for reliability and maybe to accommodate different types of ammo. Also, who knows the differences in the shell ejection between a Colt SMG style ejector and an AR15 type of ejector. I had my mill set up for milling lines in my last linear comp. Should not be hard to do an exact reproduction of the Guard upper. If this stops the ejection problem, it would make sense to use the Guard upper with the BCG/barrel/lower for a custom build. (If you don’t have a mill with a rotary table. ) |
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Posted: 2/2/2018 11:56:08 PM EDT
[#49]
I didn't look very closely but was wondering if the cam pin slot or the angle between the bolt cam pin hole and bolt lugs was different.
Probably some of both. Maybe my next one I'll use a 458 SOCOM upper receiver... |
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Posted: 2/8/2018 2:02:02 AM EDT
[#50]
Quote HistoryQuoted:
I took my new build from the CMMG Guard BCG/barrel/lower for sighting in and testing of magazines, etc. I was getting about 1 in 15 failing to eject. What kind of FTE's were you getting exactly? Was the brass staying attached to the extractor and coming forward with the bolt? I'm asking because I'm experiencing similar issues with my 45 build. Every 15 or so rounds, a spent case doesn't eject and "rides" the bolt back into battery resulting in a mangled case or stovepipe:  Attached File Attached File Attached FileI've clearanced the port to the same size as my DI45 receiver. Maybe I need to open more? I would think any interference would at least knock the brass off the bolt face and cause a jam/stovepipe, not allow it to stay seated in the bolt? I'm looking at the extractor next to see if maybe sharp edges are biting into the rim and holding onto it... |
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