Bren2---any reason to skip?

[Bret]

He volunteered no other information beyond that but has said that certain combinations of gas tube, gas plugs and barrels are not compatible for whatever reason.

I'm not an engineer.

I am an industrial engineer, so I find this interesting. From a manufacturing standpoint, you want as many of the parts as possible to be the same in order to minimize inventory carrying costs, shortages, gain economies of scale in production, etc. I'll be very surprised if the 7.62x39 gas plugs are different other than the size of the gas port holes. If something is different, it really needs to matter. Can you measure the length a diameter of your gas plug for me? If you can post a picture, that would be great.

I shouldn't have to engineer a solution to a problem that is not relegated to my sample alone.

No doubt. There are some gunsmiths that are oriented towards fixing problems. There are others that just want to check all the boxes and call it good. CZ provided you with the latter.

As far as a 'tube video goes. I can do something like that eventually when time allows but I honestly question the worth. I like this forum because people seem to care but if you go to Facebook, you have an entire forum/thread/group dedicated to fawning over a machine. The fanboy is particularly strong in the Bren Cult which is probably a byproduct of how rabid CZ fans are. I don't have time or any desire to deal with unbridled bias and stupidity. I deal with it enough on a daily basis.

I put up several Youtube videos showing firearms malfunctioning (and working too). 90% of the responses I get are people trying to help or thanking me for letting me know. As for the other 10%, I set my videos up so that I can delete stupid comments. I delete the comments and then block the posters. Problem solved.

Regardless of that, I hope that my objectivity comes across as my goal behind my posts is to share my experiences with as little bias as possible.

Absolutely it does.

I feel almost guilty writing what I wrote because the guns really are cool.

It's the truth and you gave CZ the opportunity to fix it. It's on them.

[Bret]

I fired my 11" 7.62x39 Bren 2Ms for the first time today. It ran 100%. Ejection was to about 3:30 with the spent cases going about 5' to 7'. If anything, the ejection seemed weak. There were no failures though through the 140rds of Tula 122gr FMJ that was fired. I did rotate the gas plug to the adverse setting just to see if it would make a difference. It didn't other than perhaps moving the ejection point to about 3:00. The magazines I used were a D&H 30rd, a couple of RZE Unimags and an ASC 20rd. All locked in fine and held the bolt back when they became empty.

The 7.62 gun is over gassed, horribly. Brass ejects to 12:30, basically forward. Bolt velocity is way too high.

Would I be correct to assume that the spent cases are getting chucked a good distance? If you don't mind sharing, how far are they going?

[Aries144]

My 14" 5.56 and 9" 7.62x39 Bren 2's use different pistons and cylinders. I don't know if that's a caliber thing or a barrel length thing.

14" 5.56 on top. The 9" 7.62x39 cylinder lacks the gas vent (not pictured) at the muzzle end of the cylinder and has a larger ID, and the piston a correspondingly larger OD, compared to the 14" 5.56 parts.





You can swap them, you just have to swap both piston and cylinder.

I tried the 14" 5.56 piston/cylinder on my 9" Bren 2 and noted that it functioned with a Silencerco Omega can attached in both settings. The "Normal" 5.56 setting caused brass to barely dribble out, but without malfunction in the 60 rounds used to test it. The other setting ejected the brass somewhat gently 2-3 feet to 2-3 o' clock. The gun failed to cycle in either setting with the can removed.

I thought I would note that my 9" Bren 2 hasn't seen the issues Magsz gun has- but I only have a couple hundred rounds through it at this point. Mine ejects about 6+ feet to 2-3 o' clock without can on the "Normal" gas setting and roughly the same distance to 1-2 o' clock on the same setting with a Silencerco Omega attached.

Magsz, did your 9" Bren function fine at first and then start having problems as round count increased? Gas port erosion maybe?

[Magsz]

Lots of really good stuff here.

Bret, let me try and find a video taken from in front of the firearm. You can see how violently the brass is being chucked forward. It's nothing like an AK in regard to ejecting brass to the moon but it does chuck it out of there. The problem lies in the outliers when it bounces around the ejection port and then dribbles out or goes where ever it wants to go...sometimes back into the ejection port.

Bret, I agree with you from the simple standpoint of production. It makes zero sense to produce a billion different parts unless you absolutely have to which in the case of the bren, going between calibers, you may have to beyond simply drilling different port sizes. This is way beyond my intelligence level.

I can get some measurements tomorrow when I'm off duty if I have the time. I'm not really sure that the gas port would really erode in five thousand rounds. My firing schedule was not that crazy and the gun really didn't get all that hot despite being run pretty hard. My definition of hard is that i'm not a bench shooter and 99.9% of my shooting beyond zeroing, is running drills that involve multiple rounds per evolution. The problems 'sort' of got progressively worse as the round count increased but that's not really fair to say that its a gas port issue. There ARE some other factors, ie dirt, grit, changing levels of lubricant within the firearm, broken magazines that were later chucked, new magazines and tight springs etc.

I would really be curious to run the 14 inch gas piston gubbins in my 9 inch gun.

Can someone pull their 7.62X39 bolt and check tension on their extractor for me? Mine BARELY moves when probed with a glock tool. Its "clean" and free of debris but it feels like there's a 5000000000 lb rated spring under there....

[Aries144]

Can someone pull their 7.62X39 bolt and check tension on their extractor for me? Mine BARELY moves when probed with a glock tool. Its "clean" and free of debris but it feels like there's a 5000000000 lb rated spring under there....

Mine is also very stiff. I haven't noticed any issues because of this yet.

I would expect the issue encountered with an overly stiff extractor would be a failure of the bolt to go into battery, due to a failure of the extractor to snap over the rim of the feeding cartridge.

[Bret]

My firing schedule was not that crazy and the gun really didn't get all that hot despite being run pretty hard.

When I was shooting mine yesterday, I rotated it between another pistol and rifle. Still, the front handguard got hot to the point that it was hard to hold. I can't imagine holding it in a military situation on full auto. Are people adding some sort of plastic handguards to these? Sorry for my ignorance, but I'm not a front rail type of person. I've always just purchased guns that have plastic (or wood) front handguards.

[Magsz]

Mine is also very stiff. I haven't noticed any issues because of this yet.

I would expect the issue encountered with an overly stiff extractor would be a failure of the bolt to go into battery, due to a failure of the extractor to snap over the rim of the feeding cartridge.

It could also lead to a situation where the gun doesn't want to kick the brass out, or by the time the extractor lets go, the bolt is already moving forward. This could be part of the reason why the gun will stovepipe. Hmmm...

[Magsz]

When I was shooting mine yesterday, I rotated it between another pistol and rifle. Still, the front handguard got hot to the point that it was hard to hold. I can't imagine holding it in a military situation on full auto. Are people adding some sort of plastic handguards to these? Sorry for my ignorance, but I'm not a front rail type of person. I've always just purchased guns that have plastic (or wood) front handguards.

I'm willing to bet the nerves in my hands are shot from shooting so much lol! I dont really notice the heat. I'm not saying the gun doesnt get hot but it hasn't gotten so hot that I cant hold it and if you've watched any of the videos on my channel, i'm not a one shot every five seconds kinda guy.

Here's a video taken several months ago when the gun was around 3 or four thousand rounds down the tube. The ejection has gotten worse, ie more towards 12:30-1 at the current round count of ~5100. Also, in this video, the gun is ejecting in a fairly uniform way. Now, the gun will send cases in a random rainbow anywhere between 12:30 and 5.

https://www.youtube.com/watch?v=4GXOtzMWUHo

[Aries144]

It could also lead to a situation where the gun doesn't want to kick the brass out, or by the time the extractor lets go, the bolt is already moving forward. This could be part of the reason why the gun will stovepipe. Hmmm...

I don't think so. Extractor spring tension can cause failures to extract if the spring is weak enough to slip off the rim of the cartridge during extraction. It can also cause failures to go into battery if too stiff, as the extractor would fail to snap over the case rim, preventing the bolt from going into battery. The only reason it moves is to allow it to snap over a cartridge rim during feeding.

The extractor doesn't need to, and ideally wouldn't move at all during extraction and ejection. It acts as a stationary pivot point during ejection as the ejector pushes the cartridge off the bolt face and (hopefully) out of the ejection port.

All the evidence you've shown weighs pretty heavily in favor of your gun being badly overgassed. The damage to the recoil buffer, aft end of the recoil guide rod, violent 12:30 ejection, and mention of stove pipes all scream *overgassed* to me. The only questions left in my mind are: "Is it overgassed due to port erosion or a gas port originally drilled too large?" and "Is there anything else wrong that's contributing to erratic ejection, like the front end of the receiver pinching the bolt carrier?"

ETA: if ejection has gotten that much worse it seems to confirm port erosion as the most likely culprit. Other thing to check would be the recoil spring. I'd be willing to bet that replacing the gas cylinder (possibly with one using a smaller set of ports) and the recoil spring would cure your issue.

CZ needs to get their shit together and get replacement parts in.

[Bret]

Other thing to check would be the recoil spring. I'd be willing to bet that replacing the gas cylinder (possibly with one using a smaller set of ports) and the recoil spring would cure your issue.
CZ needs to get their shit together and get replacement parts in.

I was thinking the same thing about the recoil spring. Replacing one after several thousand rounds is reasonable. CZ not having them isn't.