The Original CZ Forum
GENERAL => General Firearms Discussion => Topic started by: Crawl on June 03, 2020, 12:12:47 AM
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Firearm is a CMMG 9mm radial delayed blowback AR-style rifle with a 9" barrel. Basically, it's a proprietary BCG, barrel, and magazine that allows the use of an AR lower using modified MagPul P mags. The BCG functions similarly to an AR15 bolt. It locks into a barrel extension and uses a normal carrier.
Assembled using a Mega Arms Heavy Duty upper (really tight tolerances and super thick walls) and a Knights Armament URX 3.1 handguard. These are simply the spare parts I had on-hand for testing, so I used them.
Only fired 10 rounds through it because of one piece of brass coming out as shown below. How did this happen? What happened?
The bullet exited the barrel and hit steel at 90 yards just like all the rest. Sounded the same, flew the same. I happened to see this piece of brass, so we stopped shooting. (https://uploads.tapatalk-cdn.com/20200603/6fa94e33baf7841aee0369b85b0293ac.jpg)(https://uploads.tapatalk-cdn.com/20200603/d233657222c1bd48b117845127922a2a.jpg)(https://uploads.tapatalk-cdn.com/20200603/d76d9eaba0b4ed89b58ee3c6960a6121.jpg)
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Looks like a case fired from an unsupported chamber.
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Wasn't fully in battery when it fired.
Fairly confident that's far too much case swell for early extraction/too fast cycling.
Ask CMMG.
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My assumption is that it fired out of battery, but how is this possible in an AR? If the bolt isn't locked into the extension, how could it fire?
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Does it use a similar extractor and ejector to the AR15 bolt?
Look at the base of the case. Not the swelled (ring, which is scary as can be). The base. Is that an ejector mark on the R of LUGER? Never, ever, ever, ever, seen a 9MM make that much pressure before. That's a very hot 5.56X45/.223 Remington (or any other high pressure rifle cartridge) TOO MUCH chamber pressure ID sign.
The primer also looks like it may have had enough pressure on it to flow back into the firing pin hole in the bolt face a bit, too.
If either of those are what they look like and the case swelled up like that around the base, how much pressure would be required to do both to a case? Seems like the swelled ring would have reduced the pressure somewhat and yet it still appears to show high pressure signs on the base from the ejector (if it uses an AR15 style ejector in the bolt) and the primer cup.
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That's what I was seeing. The base looks like an over pressured 223. I just don't see how it could've ballooned out like that. Not seeing how it could fire out of battery. And if the chamber isn't supporting the case, then why was this the only one?
I've emailed it to CMMG, but I wanted to run it past you guys. It isn't making sense to me. It's almost like the barrel would have to move in order for that to happen.
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What is the marking at the very base of the Bulge
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way cool, imo.
when i see things like this its a head scratcher.
to me, it appears that maybe the bolt was not locked in place and maybe the reaction was pushing the bolt back a bit and allowing the brass to swell in the unsupported part.
If the bolt had a space when it fired, the brass would have probably separated dramatically due to the pressure spike.
but that is a keeper imo.
also, i didnt see if these were factory or home-brew?
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Did it slam fire?
Is that at stepped 9mm case? I'm trying to remember what case heads I've seen that have the stepped wall and I think A-USA was one of them. I'm wondering why this case head didn't separate? It's hard to tell in the picture.
Obviously it detonated out of battery with part of the case still in the chamber. Either the bolt is unlocking early or it slam fired before fully chambering.
What buffer and spring was used in the lower? I contact CMMG and discuss with their tech support folks to get confirmation of your build meets their requirements.
Cheers,
Toby
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Did it slam fire?
Is that at stepped 9mm case? I'm trying to remember what case heads I've seen that have the stepped wall and I think A-USA was one of them. I'm wondering why this case head didn't separate? It's hard to tell in the picture.
Obviously it detonated out of battery with part of the case still in the chamber. Either the bolt is unlocking early or it slam fired before fully chambering.
What buffer and spring was used in the lower? I contact CMMG and discuss with their tech support folks to get confirmation of your build meets their requirements.
Cheers,
Toby
^^ This for sure. While this is an interesting subject, i will bet CMMG will have an informed perspective on it.
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A USA is Armscor USA. That brass is made by them. It’s not a stepped case either.
It’s a good brass to reload. However, if the pressure is too high, fired out of battery or with an unsupported chamber, this is what will happen.
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I emailed CMMG a couple of days ago and haven't gotten a response yet. On the phone, the one guy I spoke with hadn't ever heard of this happening. I don't want to shoot the gun again unless I know how to make sure it never happens again.
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Have you removed the barrel to try and do a plank test? I know for a fact that CMMG’s barrels have short chambers. A friend had his banshee barrel reamed so he can load longer.
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Def out of battery/unsupported
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Did it slam fire?
Is that at stepped 9mm case? I'm trying to remember what case heads I've seen that have the stepped wall and I think A-USA was one of them. I'm wondering why this case head didn't separate? It's hard to tell in the picture.
Obviously it detonated out of battery with part of the case still in the chamber. Either the bolt is unlocking early or it slam fired before fully chambering.
What buffer and spring was used in the lower? I contact CMMG and discuss with their tech support folks to get confirmation of your build meets their requirements.
Cheers,
Toby
The bolt is made like an AR15 bolt. Same style ejector and extractor.
It's a normal 9mm case. Factory loaded stuff from Expansion Ammunition that has been good for the past 20k rounds or so that I've used it. I did a plunk test, and the ammo seems to do fine. There isn't enough unsupported case to explain this much expansion, so it has to be the bolt unlocking early. I'm using a carbine buffer and spring setup, as CMMG recommends. It is Armaspec's version of the silent captured spring. It has given me no trouble in my 223s. CMMG is still looking into it.
When disassembling it today, the barrel nut came off without a wrench (turned really hard with my bare hands), however, it is a Mega Arms upper...in other words, I had to use a mallet for 10 minutes just to get the barrel removed (which was not surprising because this upper has been this tight with every barrel I've tested with it). So I don't think the barrel was moving at all in the upper. Even though the barrel nut was not all the way tight, it certainly couldn't have rotated enough while firing to let the barrel come out of the upper (barrel nut is integrated into the handguard, so any rotation would not have been enough to allow the barrel to move).
I don't see how the powder charge could be the problem. I've loaded lots of Major power factor ammo. This powder can't be loaded to those pressures even with a full cartridge. I'm going to assume that the bolt opened and maybe hung up in the barrel extension somehow delaying the blowback too long. Still open to brainstorming.
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What is the marking at the very base of the Bulge
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Definitely out of battery. No Detective Columbo needed here. That is a scary looking casing. :o
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What is the marking at the very base of the Bulge
I was looking at that mark as well Doc, i can not figure out what it is. First i was thinking maybe the extractor, but it is too wide. Then i was thinking maybe the bolts breech face, but that dose not seam right ether due to the marks shape. A mystery indeed.
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What is the marking at the very base of the Bulge
I was looking at that mark as well Doc, i can not figure out what it is. First i was thinking maybe the extractor, but it is too wide. Then i was thinking maybe the bolts breech face, but that dose not seam right ether due to the marks shape. A mystery indeed.
I bet if we saw a good enhanced pic of the breechface there would be some machining in there that matches up to that pretty well.
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It seems that the there are two marks opposite each. I agree that it might be the breechface clamping on it when it detonated out of battery.
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The rifle used was a CMMG 9mm radial delayed blowback. The rear of the locking lugs have tapered cuts to facilitate unlocking but the bolt face looks just like an AR15 bolt. In the brass pictured the depression has defined ends. I would figure if the bolt face left the depression it would have tapered ends because the case was at an angle or go all the way round the case if it was inline with the bolt.
(https://i.imgur.com/klT5Zmf.jpg)
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It seems that the there are two marks opposite each. I agree that it might be the breechface clamping on it when it detonated out of battery.
Not sure what you mean by clamping. Here's a photo of the bolt.
By the way, I was able to repeat the issue this weekend during extremely slow fire.
All the various engravings at the base of the neck, just blow the donut are the inside edge of the bolt. The gaps are from where the ejector and extractor are. Also there one section on the "bottom" of the bolt face that is cut out. (https://uploads.tapatalk-cdn.com/20200608/97ec5b1edc054aa37f03353df8e69a7d.jpg)(https://uploads.tapatalk-cdn.com/20200608/0e5bb7787b7a334e9460ae657c8b1b60.jpg)(https://uploads.tapatalk-cdn.com/20200608/e060889942cb14c38a0762a2927c6d56.jpg)(https://uploads.tapatalk-cdn.com/20200608/3bfaa028e160c7486ced8bdeaa64e7f9.jpg)
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I see, i did not know about the extra cutout at the bottem, i have not seen that before. I also did not remember the ejector pin being only half way into the bolt face. It looks like a 556 bolt face is the same way, i should go clean my rifle to refresh my memory. The mark makes more sense to me now.
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Quick update to let you guys know that CMMG sent me a shipping label so that I can send them my assembled upper, which I have done. There was a note that they may need to replace the barrel. We shall see. Also, I noticed chipping on the bolt face lugs. This gun only has 25 rounds through it, so it's starting to look like a no-go.
Between this and the fact that the Scorpion fires even while on safe (because the plastic flexes too much), I may be selling it all and buying a B&T.
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That's pretty terrifying. You came close to a whodunit postmortem.
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Update:
CMMG has returned my upper with a new bolt. Their response is that they now offer a newer design, and the extractor was out of spec anyway, so they replaced it. Apparently was not a headspace issue.
You can probably see in some photos how much the tapered rear of the bolt lugs had worn after only a few dozen rounds, so I will be checking that while function and safety testing it.
If there is a new design that works better, then maybe this thing will have some staying power. The magazine seems like a failure point too, but it hasn't been an issue through the first 40 rounds. Maybe after another 2k rounds I can draw conclusions about this gun.
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Did it slam fire?
Is that at stepped 9mm case? I'm trying to remember what case heads I've seen that have the stepped wall and I think A-USA was one of them. I'm wondering why this case head didn't separate? It's hard to tell in the picture.
Obviously it detonated out of battery with part of the case still in the chamber. Either the bolt is unlocking early or it slam fired before fully chambering.
What buffer and spring was used in the lower? I contact CMMG and discuss with their tech support folks to get confirmation of your build meets their requirements.
Cheers,
Toby
The bolt is made like an AR15 bolt. Same style ejector and extractor.
It's a normal 9mm case. Factory loaded stuff from Expansion Ammunition that has been good for the past 20k rounds or so that I've used it. I did a plunk test, and the ammo seems to do fine. There isn't enough unsupported case to explain this much expansion, so it has to be the bolt unlocking early. I'm using a carbine buffer and spring setup, as CMMG recommends. It is Armaspec's version of the silent captured spring. It has given me no trouble in my 223s. CMMG is still looking into it.
When disassembling it today, the barrel nut came off without a wrench (turned really hard with my bare hands), however, it is a Mega Arms upper...in other words, I had to use a mallet for 10 minutes just to get the barrel removed (which was not surprising because this upper has been this tight with every barrel I've tested with it). So I don't think the barrel was moving at all in the upper. Even though the barrel nut was not all the way tight, it certainly couldn't have rotated enough while firing to let the barrel come out of the upper (barrel nut is integrated into the handguard, so any rotation would not have been enough to allow the barrel to move).
I don't see how the powder charge could be the problem. I've loaded lots of Major power factor ammo. This powder can't be loaded to those pressures even with a full cartridge. I'm going to assume that the bolt opened and maybe hung up in the barrel extension somehow delaying the blowback too long. Still open to brainstorming.
1 of the 1st rules of troubleshooting.... never rule out anything and that includes the user. Many people put on blinders that never look at the user.
but its your gun and you will figure it out sooner or later.
good luck
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This isn’t unusual in a blowback 9mm AR but surprising from a radial delayed setup, that’s the point, not to fire unless it’s locked.
You did right to send it back, a potentially dangerous situation.
Personally, I’d ditch the Armscor, I’ve not been impressed with any Armscor ammo. For me, brass Blazer 115 gr. Is just as cheap and more consistent, and for a few pennies more there’s much better options.
I think if I spent the $$$ for a CMMG I’d buy better ammo like MEN 124 gr. NATO. Which is far from the best, but cheap enough for cheap plinking.
I’d also avoid any aluminum cased ammo, IMHO just too soft for unsupported chambers. I have several blowback carbines that choke on Blazer aluminum but run fine on any brass or steel case.
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That's a classic out of battery fired case. Blowback AR's can be bad about it. A regular AR cannot fire OOB because the bolt rotates into lock-up before the carrier moves forward enough for the firing pin to even reach the primer. AR 9's lack the locking bolt and nothing stops the firing pin if the hammer drops and the cartridge isn't fully chambered. In my case, and many others, these OOB firings are happening when the bolt slams forward hard enough to trip the trigger sear just as the bolt is bouncing back after picking up a new round. My solution was heavier trigger and disconnector springs.
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That's a classic out of battery fired case. Blowback AR's can be bad about it. A regular AR cannot fire OOB because the bolt rotates into lock-up before the carrier moves forward enough for the firing pin to even reach the primer. AR 9's lack the locking bolt and nothing stops the firing pin if the hammer drops and the cartridge isn't fully chambered. In my case, and many others, these OOB firings are happening when the bolt slams forward hard enough to trip the trigger sear just as the bolt is bouncing back after picking up a new round. My solution was heavier trigger and disconnector springs.
I literally posted photos of the bolt...it's a standard AR15 bolt design. It locks into the barrel extension.
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This isn’t unusual in a blowback 9mm AR but surprising from a radial delayed setup, that’s the point, not to fire unless it’s locked.
You did right to send it back, a potentially dangerous situation.
Personally, I’d ditch the Armscor, I’ve not been impressed with any Armscor ammo. For me, brass Blazer 115 gr. Is just as cheap and more consistent, and for a few pennies more there’s much better options.
I think if I spent the $$$ for a CMMG I’d buy better ammo like MEN 124 gr. NATO. Which is far from the best, but cheap enough for cheap plinking.
I’d also avoid any aluminum cased ammo, IMHO just too soft for unsupported chambers. I have several blowback carbines that choke on Blazer aluminum but run fine on any brass or steel case.
As I stated originally, it isn't Armscor ammo, it was their brass. Besides that, it also happened with every brand I used (including Blazer, which is also cheap).
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Update:
Tested the rifle this weekend at the range (after firing about 800 rounds through an MP5 switching between full and semi auto), and the result is that CMMG's replacement bolt seems to have fixed the problem.
The recoil compared to the MP5 is a little greater, but it's still better than direct blowback.
I happened to be shooting next to a guy who has the same CMMG radial-delayed blowback gun, and he has had zero problems with his.
So far, so good. Seems like the new extractor fixed the problem. I'm certainly not knowledgeable enough to understand how.
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Update:
Tested the rifle this weekend at the range (after firing about 800 rounds through an MP5 switching between full and semi auto), and the result is that CMMG's replacement bolt seems to have fixed the problem.
The recoil compared to the MP5 is a little greater, but it's still better than direct blowback.
I happened to be shooting next to a guy who has the same CMMG radial-delayed blowback gun, and he has had zero problems with his.
So far, so good. Seems like the new extractor fixed the problem. I'm certainly not knowledgeable enough to understand how.
I do not understand ether but i am glad that you got it fixed. Thank you for the follow up.
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Catching up on old threads today.
Seems like the issue all along (besides parts that break easily) is that I was using a buffer with inadequate mass.
Sent from my SM-G986U using Tapatalk
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Catching up on old threads today.
Seems like the issue all along (besides parts that break easily) is that I was using a buffer with inadequate mass.
Sent from my SM-G986U using Tapatalk
Yes, you want to go heavy with blowback buffers and also consider heavier springs, such as those made by springco.
FWIW, Vltor's A5 buffer system is also something that helps control 9mm recoil and increase function/reliability - if you don't need a super short gas tube/length of pull.
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Agree with all of that. I knew what to do when I built it, but I wasn't mentally processing what was happening at the time!
I recommend sprinco springs too, and I always change springs before the buffer weight gets changed.
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Agree with all of that. I knew what to do when I built it, but I wasn't mentally processing what was happening at the time!
I recommend sprinco springs too, and I always change springs before the buffer weight gets changed.
Yeah, I didn't even think about springs not knowing much about how CMMG's recoil system on these guns works. Apparently, not as different practically from a standard blowback 9mm AR.
Springs are more about how much braking you want while bolt cycling (have to up power if upping buffer weight) and ensuring sufficient force to reliably chamber a round. Why generally you go w/ strongest spring that allows your bolt catch to activate with your weakest ammo (recognizing that bolt catch may not work if using weakest ammo when it's super cold, but should still function)...
Springcos are rate for what, 50k rounds or so? -- That's more than the lifetime of your barrel? What I like about them is you only need to replace during barrel changes vs a lot more spring changes with milspec springs and their 5k service interval.
Buffer weights are more about increasing dwell time and reducing overall felt recoil (and not just recoil duration) and generally are more important to proper function.
Me personally, while I start with a Springco Blue Spring or XP equivalent (Geissele braided, Tubb flat, etc.) for 14.5-16" DI AR15s, and H1 buffer w/ midlength and H2 with carbine and go from there -- both in carbine buffer tubes. A5 tubes are a whole different formula.
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I know this is an older thread, but I'm having similar issues with my CMMG Banshee.
I contacted CMMG by email on 12/25/22 about the Banshee firing out of battery. They responded on 12/29/22 and on 12/30/22 via email and their suggestion is to try different ammo and encouraged me to continue to fire this firearm even though I have explained to them that I believe there is a safety risk in doing so. I further explained that it’s not an ammo issue and but rather an out of battery issue. Regardless if the ammo is in spec or not, the firearm should prevent the round from firing if out of battery.
Attached are pictures of that I had sent CMMG. On 12/30/22, I requested CMMG either replace the firearm or pay me for the purchase price (I would surrender the firearm to CMMG). No response! I emailed them again on 1/6/23 and I haven’t received a response from them from that request either. I have called CMMG (660-248-2293, option 1) on several occasions since 1/6/23, including this morning, but it always goes to voicemail and as stated on their email they encourage all customer service questions being emailed to them.
I purchased this firearm in September of 2022. The firearm immediately had feeding issues with all kinds of ammo. The rear of the bottom lugs on the bolt were striking the case mouth of the loaded round in the magazine. As the bolt travelled rearward from firing, the rear of the bottom bolt lugs struck the case mouth of the loaded round in the magazine and turned it cockeyed in the magazine. When the bolt moved forward after cycling it pushed the cockeyed round out of the magazine and it failed to feed in the chamber. This happened time after time. CMMG had the firearm for about 6 weeks and resolved the feeding issue by replacing the bolt.
Does anyone have any opinions or suggestion on the matter?
(https://live.staticflickr.com/65535/52637335538_109512818b_q.jpg)
(https://live.staticflickr.com/65535/52637335448_68c497077c_q.jpg)
(https://live.staticflickr.com/65535/52637113009_bd4376b633_q.jpg)
(https://live.staticflickr.com/65535/52636340702_eb3ab9b555_q.jpg)
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The solution is a heavier buffer. It's SUPPOSED to run with a carbine buffer, but it needs an H2 at least.
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The solution is a heavier buffer. It's SUPPOSED to run with a carbine buffer, but it needs an H2 at least.
I'm having erratic ejection too. Some of the cases dribble out as it is. A heavier buffer will only create additional ejection problems. The banshee regulates the weight through the carrier by adding weights, which I have but not installed.
If the firearm fires out of battery, then adding more weight to either a buffer, or in my case, to the carrier would not solve the problem. Granted, in some instances it may reduce the chance from soft feeding or bolt bounce, but it can't cure completely the out of battery situation. That, in my opinion, would be mechanically impossible.
Regardless of the reason, it should never be able to fire out of battery. There's a lot of reasons why the banshee could go out of battery, like debris in the chamber, out of spec round, etc.
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Not sure why you think a firearm SHOULD prevent it from firing out of battery. A guy can over gas and under spring a gun and cause unsafe situations. But I do agree that it is clearly not working as advertised. Not saying yours SHOULD work like mine. There likely is some other issue. The Banshee may very well be a poor design, but mine is a dream to shoot when I buffer it adequately. They said it is designed to work with a carbine buffer...that being obviously untrue about mine indicates to me that CMMG is not necessarily as reliable as someone like AR15 Performance.
Using out of spec ammo I, by definition, asking the gun to deal with something it wasn't built for.
You may be using weaker ammo, you may not. It likely isn't your fault that it has issues. They replaced my bolt, and it didn't fix my problem. A heavier buffer and spring did fix it. It cycles even with my Minor PF handloads.
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Not sure why you think a firearm SHOULD prevent it from firing out of battery. A guy can over gas and under spring a gun and cause unsafe situations. But I do agree that it is clearly not working as advertised. Not saying yours SHOULD work like mine. There likely is some other issue. The Banshee may very well be a poor design, but mine is a dream to shoot when I buffer it adequately. They said it is designed to work with a carbine buffer...that being obviously untrue about mine indicates to me that CMMG is not necessarily as reliable as someone like AR15 Performance.
Using out of spec ammo I, by definition, asking the gun to deal with something it wasn't built for.
You may be using weaker ammo, you may not. It likely isn't your fault that it has issues. They replaced my bolt, and it didn't fix my problem. A heavier buffer and spring did fix it. It cycles even with my Minor PF handloads.
“Not sure why you think a firearm SHOULD prevent it from firing out of battery.”
To me, that gets into a whole philosophical argument on whether a manufacturer has a moral, ethical, and legal duty to protect the user from potential harm from their own design. I think, at least to some extent, they do. Again, it may not be an out of spec round that causes an out of battery issue. It could be from things like debris in the chamber or even bolt bounce (OOB while rapid firing), etc.
If CMMG believed that a heavier buffer would solve the problem, then they would’ve said it in their response on the 12/29/22 and 12/30/22 reply, but they didn’t. They simply blamed it on ammo and told me to continue to shoot it with different ammo.
“A guy can over gas and under spring a gun and cause unsafe situations.”
I agree, but now the user has altered the firearm. In doing so may relieve the manufacturer from some or all of any liability.