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[ARCHIVED THREAD] - Thoughts on the CMMG Guard? (Page 18 of 25)
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For pistol calibers, with an AR bolt, single-feed mags are much easier to feed since you're pointing them right at the chamber. With double-feed mags, especially with fat rounds and flat nose bullets, the challenge is ramping the chamber enough to prevent them from jacking up between the lugs and breech, without sacrificing too much chamber support. It's been done in 9mm with Colt mags though, so with the right mag location and feed ramp you should be able to get a double-feed mag to work. https://www.ar15.com/forums/Industry/9mm-Guard-Barrel-and-BCG-working-with-Colt-mags/145-286362/ Take a look at the MPX feed ramps for inspiration http://i678.photobucket.com/albums/vv143/SniperVIIUS/Mobile%20Uploads/FE5EF2FA-0440-405C-99A0-C1B2CB65BB6C_zpsolxwc2pi.jpg Quoted:
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Does anyone know if the BCG will work with mags other than Glock, specifically MP-5/40 mags? With double-feed mags, especially with fat rounds and flat nose bullets, the challenge is ramping the chamber enough to prevent them from jacking up between the lugs and breech, without sacrificing too much chamber support. It's been done in 9mm with Colt mags though, so with the right mag location and feed ramp you should be able to get a double-feed mag to work. https://www.ar15.com/forums/Industry/9mm-Guard-Barrel-and-BCG-working-with-Colt-mags/145-286362/ Take a look at the MPX feed ramps for inspiration http://i678.photobucket.com/albums/vv143/SniperVIIUS/Mobile%20Uploads/FE5EF2FA-0440-405C-99A0-C1B2CB65BB6C_zpsolxwc2pi.jpg |
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Quoted: One ramp in the center (think this is a .45) https://thisguysguns.files.wordpress.com/2018/11/barrelext2.jpg |
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But there are no feeding issues with people running Colt mags and Endomags? You mentioned flat nosed bullets possibly being an issue, I wonder if the Speer 147 gr. 9mm feed ok. If you want to run MP5 mags, you'll need a lower with a feed ramp that will clear the guard bolt. NFA makes a 9mm MP5-mag lower, dont' think anyone is making an MP5/40/10 mag lower. Would have to remove the ejector and clearance the upper for the wider mag feed lips. https://www.newfrontierarmory.com/shop/c-5-billet-lower/ |
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But there are no feeding issues with people running Colt mags and Endomags? You mentioned flat nosed bullets possibly being an issue, I wonder if the Speer 147 gr. 9mm feed ok. https://m.youtube.com/watch?v=dc527Z9vR6g |
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Colt lowers have built-in feed ramps, and Endomags have feed ramps integral to the conversion inserts. If you want to run MP5 mags, you'll need a lower with a feed ramp that will clear the guard bolt. NFA makes a 9mm MP5-mag lower, dont' think anyone is making an MP5/40/10 mag lower. Would have to remove the ejector and clearance the upper for the wider mag feed lips. https://www.newfrontierarmory.com/shop/c-5-billet-lower/ Quoted:
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But there are no feeding issues with people running Colt mags and Endomags? You mentioned flat nosed bullets possibly being an issue, I wonder if the Speer 147 gr. 9mm feed ok. If you want to run MP5 mags, you'll need a lower with a feed ramp that will clear the guard bolt. NFA makes a 9mm MP5-mag lower, dont' think anyone is making an MP5/40/10 mag lower. Would have to remove the ejector and clearance the upper for the wider mag feed lips. https://www.newfrontierarmory.com/shop/c-5-billet-lower/ ETA: The admin on the Q&A section of the C-5 page says MP-5/40 mags will fit. The credit card is looking at me longingly... |
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ETA: The admin on the Q&A section of the C-5 page says MP-5/40 mags will fit. The credit card is looking at me longingly...  With or without mods?
On a related note, I've been tempted to build a UMP magwell for my DI45 SBR to replace my GG magwell, for the BHO mostly. I think all the mag bodies are the same size, so it would also let me run 9, 40, 45 (and 10mm if I modify .40 mags) in the same registered, bufferless lower. Attached File |
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With or without mods?
On a related note, I've been tempted to build a UMP magwell for my DI45 SBR to replace my GG magwell, for the BHO mostly. I think all the mag bodies are the same size, so it would also let me run 9, 40, 45 (and 10mm if I modify .40 mags) in the same registered, bufferless lower. https://www.AR15.Com/media/mediaFiles/173511/IMG_20160922_202807631_jpg-977192.JPG Quoted:
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ETA: The admin on the Q&A section of the C-5 page says MP-5/40 mags will fit. The credit card is looking at me longingly... With or without mods?
On a related note, I've been tempted to build a UMP magwell for my DI45 SBR to replace my GG magwell, for the BHO mostly. I think all the mag bodies are the same size, so it would also let me run 9, 40, 45 (and 10mm if I modify .40 mags) in the same registered, bufferless lower. https://www.AR15.Com/media/mediaFiles/173511/IMG_20160922_202807631_jpg-977192.JPG There are .40 GG mags? What would you have to do to get 10mm to fit? |
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It didn't say anything about modifications, but their measurements are accurate, I don't see how you can use them without. Their C-5 upper is already opened up compared to a regular upper so that should require less fitting. There are .40 GG mags? What would you have to do to get 10mm to fit? |
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Does anyone think that the Guard bolt will handle 10mm? I’m not opposed to having the .40 Guard barrel rechambered. I might as well go full retard with this thing. Look at the difference in ramp angle on the .45 lugs vs the .40 or 9mm bolts. Hot 10mm would need a shallower ramp angle. If you try to calm it down with extra mass, that's just more stress on the rear of the bolt, the cam pin and the cam pin track. |
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I didn't think that upper had the clearance for the cam pin.  Quoted:
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I’m kicking around the idea of buying a Foxtrot Mike side charger and rebuilding it. |
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.40spec 10mm, maybe. I wouldn't run hot loads. Look at the difference in ramp angle on the .45 lugs vs the .40 or 9mm bolts. Hot 10mm would need a shallower ramp angle. If you try to calm it down with extra mass, that's just more stress on the rear of the bolt, the cam pin and the cam pin track. Quoted:
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Does anyone think that the Guard bolt will handle 10mm? I’m not opposed to having the .40 Guard barrel rechambered. I might as well go full retard with this thing. Look at the difference in ramp angle on the .45 lugs vs the .40 or 9mm bolts. Hot 10mm would need a shallower ramp angle. If you try to calm it down with extra mass, that's just more stress on the rear of the bolt, the cam pin and the cam pin track. |
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I don't think that one has the cut either.... Quoted:
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Not sure. I’m lazy so if I get NFA’s C-5 upper, most of the work is done already to clearance the mags. |
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I just asked if it will work. If not I’ll just open up a regular upper. |
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I would look through this thread and pay attention to what @Andromax has to say about the C-5 and the Guard. Quoted:
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I just asked if it will work. If not I’ll just open up a regular upper. -Gibbz G-9 upper will work if you use their G-4 cam pin and possibly removing some material from the Guard "gas key." These uppers have enough clearance for MP5 mags, but it looks like the ejection port is not long enough. I'm not too keen on the price tag, but it is what it is. Its possible that their C-4 upper will work, but I don't know if they are clearanced for wider mag bodies. -The top of the feedramps will probably need to have some material removed. The most economical option (lolz) is to buy a Bear Creek Arsenal side charging upper and do the mag clearance myself. I do have a Lantac side charger to play with, but its currently in use on my .300blk straight pull. As far as the Foxtrot Mike upper goes, all I want out of it is the charging asembly, barrel nut, and handguard. I could use the upper itself on something else and sell the barrel and BCG. I do want to know exactly how the charging assembly works. The only thing I can come up with is that a rod goes through the gas tube hole in the upper and pushes on the "gas key." |
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After rereading that thread: -Gibbz G-9 upper will work if you use their G-4 cam pin and possibly removing some material from the Guard "gas key." These uppers have enough clearance for MP5 mags, but it looks like the ejection port is not long enough. I'm not too keen on the price tag, but it is what it is. Its possible that their C-4 upper will work, but I don't know if they are clearanced for wider mag bodies. -The top of the feedramps will probably need to have some material removed. The most economical option (lolz) is to buy a Bear Creek Arsenal side charging upper and do the mag clearance myself. I do have a Lantac side charger to play with, but its currently in use on my .300blk straight pull. As far as the Foxtrot Mike upper goes, all I want out of it is the charging asembly, barrel nut, and handguard. I could use the upper itself on something else and sell the barrel and BCG. I do want to know exactly how the charging assembly works. The only thing I can come up with is that a rod goes through the gas tube hole in the upper and pushes on the "gas key." |
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... As far as the Foxtrot Mike upper goes, all I want out of it is the charging asembly, barrel nut, and handguard. I could use the upper itself on something else and sell the barrel and BCG. I do want to know exactly how the charging assembly works. The only thing I can come up with is that a rod goes through the gas tube hole in the upper and pushes on the "gas key." |
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I'm a fan of forward charging handles but I'm not a huge fan of FM's plastic charging handle setup. Quoted:
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After rereading that thread: -Gibbz G-9 upper will work if you use their G-4 cam pin and possibly removing some material from the Guard "gas key." These uppers have enough clearance for MP5 mags, but it looks like the ejection port is not long enough. I'm not too keen on the price tag, but it is what it is. Its possible that their C-4 upper will work, but I don't know if they are clearanced for wider mag bodies. -The top of the feedramps will probably need to have some material removed. The most economical option (lolz) is to buy a Bear Creek Arsenal side charging upper and do the mag clearance myself. I do have a Lantac side charger to play with, but its currently in use on my .300blk straight pull. As far as the Foxtrot Mike upper goes, all I want out of it is the charging asembly, barrel nut, and handguard. I could use the upper itself on something else and sell the barrel and BCG. I do want to know exactly how the charging assembly works. The only thing I can come up with is that a rod goes through the gas tube hole in the upper and pushes on the "gas key." |
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I do want to know exactly how the charging assembly works. The only thing I can come up with is that a rod goes through the gas tube hole in the upper and pushes on the "gas key." He has pictures of a stripped FM upper; gives a good idea on how it works. |
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Take a look at GatMo's post on Page 11 of this thread, about 1/3 of the way down: https://www.ar15.com/forums/AR-15/Foxtrot-Mike-s-9mm-upper-anyone-heard-of-them-/15-715196/?page=11 He has pictures of a stripped FM upper; gives a good idea on how it works. Quoted:
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I do want to know exactly how the charging assembly works. The only thing I can come up with is that a rod goes through the gas tube hole in the upper and pushes on the "gas key." He has pictures of a stripped FM upper; gives a good idea on how it works. |
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Do you guys think that the CMMG RDB 9mm would still work if I cut down the barrel to 4" or 4.5"? CMMG's shortest offering is the 5" 9mm barrel. I have longer barrel lengths but was wondering how dependent the RDB system is on barrel length if I cut one down.
Thanks |
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Do you guys think that the CMMG RDB 9mm would still work if I cut down the barrel to 4" or 4.5"? CMMG's shortest offering is the 5" 9mm barrel. I have longer barrel lengths but was wondering how dependent the RDB system is on barrel length if I cut one down. Thanks |
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I think it would still work because I think the bolt angles are too 'aggressive' for 9mm giving it a large operating window. Discussed in detail about 1/2 the page down on this page: https://www.ar15.com/forums/armory/Straight-blowback-is-100-unacceptable-imo/48-500494/&page=2 Not in the near future, but if I decide to go short, maybe ill go really short in to the 4-4.5" length. I already have a ~10" RDB upper, and it runs great and eats everything, better than my Oly. But want a tiny little package so it isnt as long when I put the can on it. Thanks for all the info and all the great work and research. |
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Opening up this magwell is going to take forever. https://media1.tenor.com/images/a037f8cd464709f3dea1203688640aae/tenor.gif?itemid=3376697 |
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You need a mill... Quoted:
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Opening up this magwell is going to take forever. https://media1.tenor.com/images/a037f8cd464709f3dea1203688640aae/tenor.gif?itemid=3376697 |
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Quoted:...The issue now is whether or not the ejector spring is going to hold up.
The .40SW uses a new rounded ejector. I used to have a .45 ACP gas operated upper by RMW. He cut the face of the ejector to have an angle to help kick the brass out at the correct angle. I'm guessing CMMG is basically doing the same thing here but by making it rounded they don't have to deal with 'indexing' of the pin. The spring appears to be identical to the proprietary spring used in the 9mm and 45ACP Guard. So I would think that using my preferred buffer/spring/tube combination would result in a short life but that is yet to be determined. I first ran the 40SW BCG in .40SW to get that dialed in. I then did the testing above. So the ejector spring probably has about 300 rounds of mixed .40SW and 9mm run through it. It seems weaker than out of the box but not weak enough to be replaced yet. 40SW is higher pressure than 9mm so I would think it should die faster in 40SW than 9mm. It will be amazing if for some reason going to a rounded ejector extends the ejector spring life. Maybe less surface area contacting the 9mm case.?... Have you decide on what ejector spring would last the longest on a regular CMMG Guard? The .45 from CMMG? Have you tried any of the heavier .556 springs from Tubbs or Sprinco that say they will far outlast normal AR springs? Will the fixed ejector be available for sale? Thanks |
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http://c3junkie.com/?page_id=954#6-22-19_update Quoted:
Hi Amphibian, Have you decide on what ejector spring would last the longest on a regular CMMG Guard? The .45 from CMMG? Have you tried any of the heavier .556 springs from Tubbs or Sprinco that say they will far outlast normal AR springs? Will the fixed ejector be available for sale? Thanks Quoted:
Quoted:...The issue now is whether or not the ejector spring is going to hold up.
The .40SW uses a new rounded ejector. I used to have a .45 ACP gas operated upper by RMW. He cut the face of the ejector to have an angle to help kick the brass out at the correct angle. I'm guessing CMMG is basically doing the same thing here but by making it rounded they don't have to deal with 'indexing' of the pin. The spring appears to be identical to the proprietary spring used in the 9mm and 45ACP Guard. So I would think that using my preferred buffer/spring/tube combination would result in a short life but that is yet to be determined. I first ran the 40SW BCG in .40SW to get that dialed in. I then did the testing above. So the ejector spring probably has about 300 rounds of mixed .40SW and 9mm run through it. It seems weaker than out of the box but not weak enough to be replaced yet. 40SW is higher pressure than 9mm so I would think it should die faster in 40SW than 9mm. It will be amazing if for some reason going to a rounded ejector extends the ejector spring life. Maybe less surface area contacting the 9mm case.?... Have you decide on what ejector spring would last the longest on a regular CMMG Guard? The .45 from CMMG? Have you tried any of the heavier .556 springs from Tubbs or Sprinco that say they will far outlast normal AR springs? Will the fixed ejector be available for sale? Thanks I have all this documented here: http://c3junkie.com/?page_id=954 I've also put some updates on that page. Regarding the .40SW bolt / ejector etc... http://c3junkie.com/?page_id=954#40SW I also added an update from over the weekned here: http://c3junkie.com/?page_id=954#6-22-19_update I'll just post that update below. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Put some more rounds through the .40SW bolt and measured the current strength of the ejector spring. Almost 6 lbs. In my experience, once you get under 5 lbs is where you will start having issues with the 9mm when using my preferred buffer / tube / spring configuration that runs in the 600s. However, I don't know what effect the rounded ejector will have.the spring is already holding up better than anything else I have tested. My modified 5.45 bolt with angles similar to the .40 SW killed the ejector spring in less than 100 rounds. While it was a standard 5.56 ejector spring, I would still anticipate a factory Guard spring to die relatively quickly. The rounded ejector may also continue to work properly once the spring gets under 5 lbs as well. I won't know till it has gotten to that point.  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> In regards to the fixed ejector, I spoke to my friend about it a couple weeks ago and he hasn't made a decision if he wants to do the mods and supply the parts at this time. |
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Thanks for the reply. Yes, I have read and studied your blog, great information. But for the bottom line on a standard Guard, a .45 CMMG ejector spring is the best choice?
When measuring spring tension, is your measurement when the spring first moves? Above 5 lbs and should be good to go for, say, a 200 round match? A 400 round match? Other than spring measurement, is there another way to judge how the spring is working, like brass distance and angle? Thanks again |
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Thanks for the reply. Yes, I have read and studied your blog, great information. But for the bottom line on a standard Guard, a .45 CMMG ejector spring is the best choice? When measuring spring tension, is your measurement when the spring first moves? Above 5 lbs and should be good to go for, say, a 200 round match? A 400 round match? Other than spring measurement, is there another way to judge how the spring is working, like brass distance and angle? Thanks again I'm measuring to when the ejector is pushed down to be flush with the bolt face. The Guard seems to kick brass out at inconsistent angles even w/ a new spring. I think when brass starts to trickle out, it is definitely time to change. When you say above 5 lbs, I assume you mean above five and under 6? Since a new spring is over 8lbs. I'm not really sure how to answer that as I documented those ejector spring strengths right before I got the fixed ejector setup. I just know it was still working fine at 5lbs. I think the bigger question is if just rounding the ejector on the 40SW extends the life somehow. The pin is the same as 556 other than it being rounded so anyone should be able to copy it and see. According to my previous testing, I would think the .40SW spring should have been killed already. |
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I'm still trying to figure out how it would kill an ejector spring unless it's being over-compressed? Is the ejector stroke longer on the guard than on any other AR?
I've never had ejection issues in my DI .45, where I'm using an opened-up 7.62x39 bolt/extractor and a slightly sloped ejector. With the slower bolt speed, I could see the smaller diameter 9mm cases clearing the chamber and starting to tilt before hitting the extension lugs, losing some angular momentum from the ejector before it has room to leave the bolt. |
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I'm still trying to figure out how it would kill an ejector spring unless it's being over-compressed? Is the ejector stroke longer on the guard than on any other AR? I've never had ejection issues in my DI .45, where I'm using an opened-up 7.62x39 bolt/extractor and a slightly sloped ejector. With the slower bolt speed, I could see the smaller diameter 9mm cases clearing the chamber and starting to tilt before hitting the extension lugs, losing some angular momentum from the ejector before it has room to leave the bolt. Look about 1/2 the way down. Basically, the lugs can move a slight bit before being being delayed so it the ejector pin is like the passenger in car going 2000 MPH and its a brick wall. |
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We were discussing theories here: https://www.ar15.com/forums/armory/Full-Auto-CMMG-Guard-Tuning/23-494385/&page=3 Look about 1/2 the way down. Basically, the lugs can move a slight bit before being being delayed so it the ejector pin is like the passenger in car going 2000 MPH and its a brick wall. How far can the ejector compress before the notch bottoms on the ejector detent pin? Enough to over-compress and fatigue the spring? |
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Quoted: If that were the case, I would think you would see some major wear in other areas, like the lugs or cam pin. How far can the ejector compress before the notch bottoms on the ejector detent pin? Enough to over-compress and fatigue the spring? If you look at the last post I made on page 2 of that thread, I also said, "I also noticed the ejector retaining pin was notched pretty hard...may get sheared off if shot more." I don't know quantitatively how far it can move but clearly it was getting beat up. |
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Yeah...I don't see any major wear anywhere. If you look at the last post I made on page 2 of that thread, I also said, "I also noticed the ejector retaining pin was notched pretty hard...may get sheared off if shot more." I don't know quantitatively how far it can move but clearly it was getting beat up. Would prevent the bolt jump from loose headspace. |
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Quoted: I wonder if some cam slot / lug adjustments could be made to make the lockup tighter without jamming up on longer cases? Would prevent the bolt jump from loose headspace. |
| Geez. Considering buying my first PCC, skimmed through this thread. Some crazy ass ideas on here. Make a 10mm, can I use a .40, feed ramp this, left handed that, spring weights, can I cut my barrel down, I lost velocity, altering mag wells, why Glock mags, blah, blah, blah. Haha. Gotta give it up to the hardcore dudes but why not just buy one off the shelf in 9mm or .45 and run it? |
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Geez. Considering buying my first PCC, skimmed through this thread. Some crazy ass ideas on here. Make a 10mm, can I use a .40, feed ramp this, left handed that, spring weights, can I cut my barrel down, I lost velocity, altering mag wells, why Glock mags, blah, blah, blah. Haha. Gotta give it up to the hardcore dudes but why not just buy one off the shelf in 9mm or .45 and run it? |
| Found this thread on a different page. Tough going through the 18 pages. But I want to build a dedicated 9mm AR-9. I want to get the CMMG RDB BCG and barrel combo, but it says that I need a widened ejector port. Don't really want to spend the $1500 on the complete banshee. Can i use an Areo Precisions M4E1 upper with the radial delay blowback BCG? Also anything special I need to get to compensate for the BCG? Lighter spring? |
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Found this thread on a different page. Tough going through the 18 pages. But I want to build a dedicated 9mm AR-9. I want to get the CMMG RDB BCG and barrel combo, but it says that I need a widened ejector port. Don't really want to spend the $1500 on the complete banshee. Can i use an Areo Precisions M4E1 upper with the radial delay blowback BCG? Also anything special I need to get to compensate for the BCG? Lighter spring? The beauty of the CMMG RDB setup is nothing special needed for it besides the proprietary barrel and BCG combo. Standard carbine spring and buffer are what CMMG supply with their factory offerings so that's a good starting point. Or you can just go straight for the "amphibian special" detailed in this thread. Just do a search for the parts list. Use any AR trigger you want, no need for the special "PCC" or "AR9" triggers some mfg have. Glock mag lowers work great just remove the fixed ejector. I prefer a standard AR lower with Endomags though. Those are fantastic. |
[ARCHIVED THREAD] - Thoughts on the CMMG Guard? (Page 18 of 25)
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