POLL: 7.62x39 Bren 2 Failures to Extract / Eject / Stovepipes -- Or Not

[czkyle1776]

It's too bad that the Bren 2 (and most other such guns) don't have an FAL style gas regulator with multiple orifices that you can just dial in at will.  Maybe somebody will come up with such in the aftermarket, but we can't even get spare gas plugs to play with (or ANY spare parts) from CZ USA at this point, which is ridiculous.

This is the Parker Mountain thing for the SCAR, they also have multiple gas jets for sale with different orifice sizes. Quite a system but looks like that would be quite a job to screw with to get it to work on a Bren 2.

https://www.parkermountainmachine.com/store/p464/Scar_16%2F17%2F20%2FSC__Gas_Jet_Tool.html

I love this about the XCR. You can really fine tune your gas settings with a ton of adjustments. Not all ammo plays nicely at predetermined gas settings, so if you get a batch of ammo that runs at gas setting "4" but the next runs better at "3" you can adjust as needed. I don't know why more manufactures don't do this. Maybe they don't trust the end user to know how to adjust? I digress...

[dkozy]

I’ve been told it’s about a $25 job got a competent gunsmith.

I've tried calling around and a few said they wouldn't touch it. I tried to drill out the adverse hole in order tap it for a stainless steel set screw in order to be able to adjust the gas system by putting in different set screws with different holes drilled through them, Unfortunately I was trying to drill through the adverse #2 hole and couldn't get through. Not sure what bits I have but the material seems EXTREMELY hard and looked like it wanted to chip away versus cut so i gave up. Any gunsmiths on here know what this gas regulator sleeve is made of? and how to cut through it?   

[Wobbly]

I believe it's a powdered metal part. They can be extremely tough. You might eventually get a drill bit through it with enough lube and time, but you probably won't be tapping threads into it.

Great idea though.

[dkozy]

I believe it's a powdered metal part. They can be extremely tough. You might eventually get a drill bit through it with enough lube and time, but you probably won't be tapping threads into it.

Great idea though.

Thank you! I've got pretty good drill bits but im not willing to destroy them over this. I underestimated the hardness of it for sure. I'm extremely curious if someone with the means could recreate the part with billet steel in order to tap it for the set screws. This would allow a wide variety of different gas settings via different set screws.   

[Wobbly]

Thank you! I've got pretty good drill bits but im not willing to destroy them over this. I underestimated the hardness of it for sure. I'm extremely curious if someone with the means could recreate the part with billet steel in order to tap it for the set screws.
 

Any machine shop could make the part, but....
• There's no way to know the stress on the part and therefore select the correct steel alloy
• Being a gun part, the liability might be too high for most shops. Lawn mower part - no problem; gun part - big problem.


Another solution might be to skip the threads altogether. Drill as proposed, then counter sink. The fact that the bolt rides inside a bolt carrier keeps the orifice in place. The orifice could be made from common flat head rivets, drilled to multiple diameters through the center as you proposed.

 

[dkozy]

Thank you! I've got pretty good drill bits but im not willing to destroy them over this. I underestimated the hardness of it for sure. I'm extremely curious if someone with the means could recreate the part with billet steel in order to tap it for the set screws.
 

Any machine shop could make the part, but....
• There's no way to know the stress on the part and therefore select the correct steel alloy
• Being a gun part, the liability might be too high for most shops. Lawn mower part - no problem; gun part - big problem.


Another solution might be to skip the threads altogether. Drill as proposed, then counter sink. The fact that the bolt rides inside a bolt carrier keeps the orifice in place. The orifice could be made from common flat head rivets, drilled to multiple diameters through the center as you proposed.

 

That's exactly what I was afraid of. Im no engineer but that part could be under some decent stress. I see what you're saying with the rivets though. 

[steves2]

I have an 11” Bren 2s in 7.62x39, made in 2019, with original hand guards. I shoot mostly Tulammo, with some Barnul, and some S&B.
My cases mostly eject at 1-2:00. The gun is over gassed, but I haven’t had FTEs.

[Bren2s]

 Hello everyone!
First post here, I've had a bren 2s, 7.62x39,  9 inch with a mempro site for a year and no issues. Probably 300 or so rounds including a most recent 4 mag dump.  All tula, herters and cheap brass cased ( 40 rounds of ZVS from Macedonia) ammo. Shot a mixture of soft point, hollow points and ball. 122 gr, 124, 143 gr, etc. No issues. No mods other than the optic, magpul rail panel covers and SBA3

[MeatAxe]

To recap, in the 3 or so years that the semi auto Bren 2 has been imported to the US, the consensus is now that the FTE malfunctions in 7.62x39 guns are caused by over-gassing (probably from over-sized gas ports) and/or failed extractors / springs (caused by swarf and crud in the extractor channel, probably from the factory).

Unfortunately, CZ USA has done little to nothing to provide parts or service to fix these guns. Fortunately, HBI seems to have come up with a fix for the over-gassing by drilling a smaller gas port in the gas tube position #3 and providing a stiffer piston spring, which seems to have fixed the problem, at least for most guns with FTE problems.

Until CZ fixes the problem itself, it would be useful for Bren 2 owners to share info on their particular caliber, round count, barrel length, the measured size of their gas ports and whether or not they’re having malfunctions, etc. Pin gauges are an easy way to accurately measure gas port sizes.

Mine is an 11” 7.62x39 with @ 1,000 rounds and no FTE malfunctions, so far. Gas port #1 = @ 0.0745” (1.89mm). Position #2 = 0.097” (2.46mm).

[MeatAxe]

Here’s another one:

16” 5.56 caliber Bren 2 carbine:

#1    0.071” (@ 1.8034mm)

#2.   0.096”  (@ 2.44mm)

NOTE: has a different diameter piston than the x39 model.

[Sean1]

Does anyone know the PSI blowing through those ports? I'm working on an adjustable gas port and wanted to get a general idea of the amount of stress that will be subjected on internal parts.