Author Topic: 7.62x39 fix??  (Read 7341 times)

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Offline Bret

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Re: 7.62x39 fix??
« Reply #15 on: August 29, 2022, 08:45:50 PM »
At this point it's clear that they're choosing new production over fixing guns that their customers already have.  I'll never buy a newish model Sig again and it looks like I'll be doing the same for CZ.

Offline A_Bren_tobeatallothers

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Re: 7.62x39 fix??
« Reply #16 on: September 05, 2022, 05:52:53 AM »
So I return years later to see CZ still has not fixed this issue? Good grief. I had an entire truck custom ordered and built and delivered in four months. I do not accept "supply chain" issues as an excuse. I'm going to to test fire mine today and see what it will do.  I lucked up I think, and found an ammo that seems to cycle well in my machine. Some Wolf. I don't remember specifics.

Offline MeatAxe

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Re: 7.62x39 fix??
« Reply #17 on: September 05, 2022, 12:50:34 PM »
So I return years later to see CZ still has not fixed this issue? Good grief. I had an entire truck custom ordered and built and delivered in four months. I do not accept "supply chain" issues as an excuse. I'm going to to test fire mine today and see what it will do.  I lucked up I think, and found an ammo that seems to cycle well in my machine. Some Wolf. I don't remember specifics.


My 11” x39 hasn’t had any function issues (knock on wood), but it’s sitting collecting dust in the safe because I don’t dare shoot it lest it breaks some small part, because there are virtually no parts available from CZ USA.

The extractor has been zeroed in on as a possible cause or contributor to the x39 malfunctions — because they came from the factory filled with crud and swarf and with mangled extractor springs — good quality control, there, CZ!

I thought about disassembling the extractor and cleaning it out as preventative maintenance. But I don’t dare try that in case the extractor spring pops off into outer space…because there are no such parts available from CZ.

So the gun just sits because, as far as I know, it’s still (probably) functional in case I need to use it (I hope).

Offline Bret

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Re: 7.62x39 fix??
« Reply #18 on: September 08, 2022, 07:23:15 PM »
Today I received a FedEx shipping notice from CZ-USA.  I have not purchased anything from them recently, so I'm hoping it's the gas valve.  The package weighs just one pound, so that's a good sign.  I'm keeping my fingers crossed.

Offline MeatAxe

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Re: 7.62x39 fix??
« Reply #19 on: September 08, 2022, 11:25:13 PM »
Today I received a FedEx shipping notice from CZ-USA.  I have not purchased anything from them recently, so I'm hoping it's the gas valve.  The package weighs just one pound, so that's a good sign.  I'm keeping my fingers crossed.

Well, that’s interesting. Unless you have some special pull with CZ, as far as I’ve seen, the 7.62x39 gas tubes for the Bren 2 have never been listed or offered for sale on the CZ USA Webstore, nor even listed for notification when (if) they ever come into stock.

Let us know what you get! If you get the gas tube, please measure the sizes of the gas ports for us!

Offline Bret

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Re: 7.62x39 fix??
« Reply #20 on: September 09, 2022, 09:07:00 AM »
I certainly have no special pull.  Perhaps they're not listing them for sale until all of the repair back orders are fulfilled.  I was already planning on measuring the gas port hole diameters.  I'll definitely let y'all know.

Offline America_First

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Re: 7.62x39 fix??
« Reply #21 on: September 09, 2022, 12:26:29 PM »
I'll post it here like I've been posting everywhere else.

The gas regulator was never the issue.  Study the 807-trials & testing, and watch the early, Pakistani promotion videos.  The Bren 807 / Bren 2S / Bren 2Ms in 7.62x39 were always over-gassed, and normal ejection was 1 - 1:30, per the engineers who designed it.

My Bren 2S was used by HBI to solve the FTE issue, and was used in the creation of the HBI piston spring & suppressor gas-port sizing.  They found the problem, within a week, which was the ejector spring channels of the bolts, had metal shavings & debris left from the factory.  This caused the ejector springs to bind, not allowing the ejector to fully extend, and with the very over-gassed nature of the firearm; only highlighted the simple QC issue even further. 

Prior to HBI solving the issue with my firearm, and multiple others in their possession they used for testing, I couldn't fire a string of 5-rounds without an FTE. 

To date, I've fired over 2,500 rounds without an FTE, both suppressed & unsuppressed, brass cased & steel cased ammunition.  My Bren 2S still has the original, prototype piston spring, which the production spring was an improvement. 

Hopefully this has helped someone.  HBI did not release this info, in my opinion, because likely CZ-UB / CZ-USA did not have the capabilities of handling a mass recall with no spare parts on hand.  Just speculation, but likely not far off. 
« Last Edit: September 09, 2022, 12:31:48 PM by America_First »

Offline Bret

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Re: 7.62x39 fix??
« Reply #22 on: September 09, 2022, 01:46:01 PM »
The gas regulator was never the issue.  Study the 807-trials & testing, and watch the early, Pakistani promotion videos.  The Bren 807 / Bren 2S / Bren 2Ms in 7.62x39 were always over-gassed, and normal ejection was 1 - 1:30, per the engineers who designed it.
Reliability aside, I'd say that over gassed is an issue.  Plus, mine and others that I've seen are not actually ejecting to 1:00 to 1:30.  The spent cases are hitting the rear of the ejection port or the case deflector and then going forward.  That points it to being over gassed resulting in too much bolt carrier velocity.  I can't see the logic behind them intentionally doing this.

Quote
My Bren 2S was used by HBI to solve the FTE issue, and was used in the creation of the HBI piston spring & suppressor gas-port sizing.  They found the problem, within a week, which was the ejector spring channels of the bolts, had metal shavings & debris left from the factory.  This caused the ejector springs to bind, not allowing the ejector to fully extend, and with the very over-gassed nature of the firearm; only highlighted the simple QC issue even further.
Is it difficult to remove the ejector and clean out the spring channels?  It's been so long since I've looked at mine I can't remember the setup.  I'd like to knock this out while I'm installing the new gas valve.

Quote
To date, I've fired over 2,500 rounds without an FTE, both suppressed & unsuppressed, brass cased & steel cased ammunition.  My Bren 2S still has the original, prototype piston spring, which the production spring was an improvement. 
This is very encouraging.  I really like this rifle, so I hope that I have your good fortune.  I definitely appreciate the insight.

Offline Bret

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Re: 7.62x39 fix??
« Reply #23 on: September 10, 2022, 03:27:01 PM »
Here's the new gas valve.  There are three holes instead of two like the old gas valve.  The "normal" one is visually smaller than the normal one on the old valve.  Unfortunately, all of the holes are larger than my rod set.  All I can really say for sure is that all are greater than 0.060".  I did use calipers to compare the two normal size holes.  Obviously the measurement wouldn't be accurate, but I can say that the new gas valve normal hole is about 0.015" smaller than the old gas valve normal hole.



Offline Bret

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Re: 7.62x39 fix??
« Reply #24 on: September 10, 2022, 04:17:57 PM »
I disassembled the extractor from the bolt in order to see if there was any debris.  It was actually pretty clean in there, but the piece of rubber or whatever it is inside the extractor spring seems to be bulging out so much that portions of it are mashing out between the spring coils.  I actually cut a bit off because it was coming through so much.  I noticed a burr on another part that I don't know what it's for or what could have caused it.  It's shown in the final picture.  Any idea what that's about?




Offline MeatAxe

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Re: 7.62x39 fix??
« Reply #25 on: September 11, 2022, 11:45:52 AM »
Here's the new gas valve.  There are three holes instead of two like the old gas valve.  The "normal" one is visually smaller than the normal one on the old valve.  Unfortunately, all of the holes are larger than my rod set.  All I can really say for sure is that all are greater than 0.060".  I did use calipers to compare the two normal size holes.  Obviously the measurement wouldn't be accurate, but I can say that the new gas valve normal hole is about 0.015" smaller than the old gas valve normal hole.





Excellent!!! Maybe CZ is finally coming through with these! So, I take it you have a 7.62x39 Bren 2 with an 11” barrel? Let us know how this new gas tube works in your gun!

Yeah, the most accurate way to measure the gas port sizes is with a set of plug pin gauges. Hopefully, you can get your hands on a proper-size set and measure the old vs new gas port holes. Here’s a relatively inexpensive set for .061” up to .250”:

https://www.amazon.com/061-250-Steel-Minus-Gauges-Metal/dp/B00FW73VXO

I had measured the gas port hole sizes on my (so far functioning) 11” barrel x39 Bren 2Ms a while back:

https://czfirearms.us/index.php?topic=118773.0

« Last Edit: September 11, 2022, 12:01:46 PM by MeatAxe »

Offline MeatAxe

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Re: 7.62x39 fix??
« Reply #26 on: September 11, 2022, 12:17:38 PM »
I disassembled the extractor from the bolt in order to see if there was any debris.  It was actually pretty clean in there, but the piece of rubber or whatever it is inside the extractor spring seems to be bulging out so much that portions of it are mashing out between the spring coils.  I actually cut a bit off because it was coming through so much.  I noticed a burr on another part that I don't know what it's for or what could have caused it.  It's shown in the final picture.  Any idea what that's about?






Interesting! My 11” x39 Bren has not had any function issues (knock on wood), but I don’t dare disassemble the extractor lest I break or lose any of the parts, which of course, the spares are non-existent from CZ. If it ain’t broke, don’t fix it, so my gun sits collecting dust, awaiting access to spare parts.

Offline Bret

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Re: 7.62x39 fix??
« Reply #27 on: September 13, 2022, 06:53:06 PM »
I ordered a different pin gauge set to match the smaller one that I already have.  It should be here next week.

Offline Bret

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Re: 7.62x39 fix??
« Reply #28 on: September 18, 2022, 10:46:12 PM »
I received my pin gauge set and measured the holes in the gas valves.  The results are below.

Old gas valve:
Normal = 0.075"
Adverse = 0.097"

New gas valve:
Normal = 0.063"
Adverse 1 = 0.071"
Adverse 2 = 0.087"

Unfortunately, I can't try it next weekend, but I will as soon as I can using the same ammunition I used before. 

Offline MeatAxe

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Re: 7.62x39 fix??
« Reply #29 on: September 19, 2022, 01:21:06 AM »
I received my pin gauge set and measured the holes in the gas valves.  The results are below.

Old gas valve:
Normal = 0.075"
Adverse = 0.097"

New gas valve:
Normal = 0.063"
Adverse 1 = 0.071"
Adverse 2 = 0.087"

Unfortunately, I can't try it next weekend, but I will as soon as I can using the same ammunition I used before.

Awesome! Thanks for posting that! Let us know how it shoots when you get a chance.

I got the same measured results on my original 2 position gas tube (we both have 11” bbl. 7.62x39 Brens).

Good to see that CZ is finally addressing the over-gassing issue and is narrowing the gas ports accordingly. Hope CZ starts making this revised 3 position gas tube available to all of us soon.

Still would be good to know what size hole HBI is drilling their 3rd position gas port to, by comparison, so if anyone has that info, please post it.

« Last Edit: September 19, 2022, 02:15:17 PM by MeatAxe »