Need help with semi auto L4A4

[WallyG.]

Greetings: It's been a while... here are some observations from my experiences to date with HA manufactured Semi Auto Brens.

1. The gas cylinder should not be wobbly in the receiver body... it should be rock solid. Why? Hard to diagnose from a distance - both physically and time since manufacture.
2. HA guns typically have the gas port in the barrel enlarged - size may vary depending on the gun.
3. Typically, only one gas port setting on the gas nut is enlarged from the standard size and that is one to "match" the enlarged barrel port - providing more gas to power the SA internals that weigh much more than the standard internals and also to overcome the introduction of the striker spring to the recoil system. Note: HA guns typically have the "as built" recoil buffer assembly removed to accommodate the striker spring length and the striker - which also acts as a recoil buffer but one of a simpler design and being physically present between the bolt and the rear of the receiver.

Different gas settings in an original Bren (once sufficient gas is provided to successfully cycle the action/internals) that provide more gas should still function but just beat your shoulder and the gun up from the excessive recoil impulse. I have read opinions that gunners used to run their guns over gassed to eliminate the possibility of a short stroke failure during combat. Too much gas should not cause feeding issues. The original gun as designed just absorbed the heavier rearward impulse force and the recoil spring returned the bolt in the cycle with the same force regardless of the bolt and carrier's recoil force level. Two independent cycles in play... one rearward and one forward.

You may very well have a damaged striker spring in your system... they can get crushed... and if damaged it might nor provide sufficient return impulse to the bolt... causing miss feeds. HOWEVER, since this is a .308 (is that right?) magazine feed lip geometry and the .308 cartridges might come into play... do you get the failures on all mags? How many have you tested in your gun?

Food for thought..

Best of luck...

WallyG.

[SleepyDoc]

Sorry, The op rod/piston that screws into the bolt carrier is wobbly. Not the cylinder. Seems like it should be OK, but I may disassemble it and see if it can be inserted m ore and if this will affect it at all. Will have to see how it aligns with the exhaust ports. IF you are uncertain what I am talking about due to my lack of appropriate terminology, it is the last picture I posted. The bolt carrier has a piston that screws into it followed by a pin to keep it from rotating out. That is slightly wobbly. Any adjustments to be made with regard to that piece?

Yes, 308 gun. I have shot a couple different mags, but I can work with it again to see if there is an issue with the mags. I have 11 in total, I think, so I can try to run a few through each when I get the chance. Hopefully in early February I can take all my projects to the range to infuriate me all at once.

The striker return spring does not appear to be damaged. Any idea on specs of springs I might need if I wanted to replace them?

I can try to set the gas on 4 and see what happens, but what is the risk of using the gun on 4 all the time? Am I inviting failure and breakage given that this is not an original gun? Will it be more likely to destroy parts given that the pieces are essentially fit to work instead of their original intention?

[WallyG.]

Hello:

Wobbly gas piston should not be a problem except a loose fit between the piston and the cylinder will allow gas to escape around the piston - reducing the rearward impulse and potentially requiring a higher gas setting to run the gun. This type of fit/wear issue is why there are multiple gas nut channel sizes in the original design.

I did not clearly communicate. I have never seen a gas nut where HA has drilled out all 4 of the gas channels to oversize... usually it is just one. So, when you say you are going to use setting 4... if HA drilled out channel #2 to oversize... 4 might not actually be allowing more gas than the drilled out 2 setting. You would need to determine if your barrel gas port is reamed out to be larger than as issued... and which if any gas nut setting has been drilled out to oversize... AND.. compare the gas channel sizes in the gas block itself (channel that feeds the gas nut) on the barrel to see if that channel was also drilled out oversized... all of this is just to determine if the gun has had its gas system modified to allow more gas into the cylinder to power the semi auto internal cycling. You need to find the combination of elements that allows the most gas and test this for feeding function... if max gas does not sufficiently recoil the internals to allow for reliable feeding... it could still be multiple contributing elements... spring issues... not enough gas, magazine feed lip/round positioning issues... if hand cycling the action provides reliable feeding of rounds, then running the gun should too. If not then each element(s) need to be investigated in the search for the cause(s).

"but what is the risk of using the gun on 4 all the time?" This is the scenario I mentioned regarding gunners running their guns over gassed... it can lead to damage of internals over time... in the case of a semi auto of HA design... potential crushing of the striker spring comes to mind. All of my focus on the gas channel sizes is to allow you to accurately determine what combinations really provide more or less gas... and whether the barrel and gas nut have been modified for semi auto use in a HA semi auto system. If you have a barrel or gas nut that is unmodified... this could be part of your problem in adjusting the amount of gas needed to power the HA semi design. Systematically assess each system element against a known original configuration part or specification. Good luck!

[WallyG.]

Have reread this thread in search of clues... the most recent discussions are about gas pressure and spring pressures... all potential contributors as they impact internal cycling and timing. Multiple adjustment options involved. However, if this is a Mk3 Bren receiver reconfigured to emulate a .308 L4... then there are some fundamental differences involving the bolt and associated parts, the ejector, the receiver feed lip supports, and the magazine feed lips between the Mk3 and a true as built L4 receiver. Are you trying to use .308 L4 Bren mags? A Mk3 was not set up originally to feed from these so there are potential geometry issues between the component parts of the Mk 3 gun body itself and the L4 magazines. Many of my running .308 Brens use South African .308 barrels and the Hungarian Zb 39 magazine. I have running versions of this combination of elements. Len has not always had success with Mk3 receivers feeding from L4 mags... I have one "converted" receiver that was abandoned for semi auto function using L4 mags as it would just not feed .308 from a L4 magazine. I have not yet tried to reconfigure it into another configuration of parts and calibers. Originally, the South Africans modified the feed lip supports of their Mk II's - converting the receivers... they also modified the mag wells to use L1A1 FAL magazines... and filled in portions of the receiver feed ramp area directly above the barrel... so even their engineers realized that a .303 receiver needed specific modification to allow it to reliably feed .308 rounds... and their barrels were designed to interact with all of their modifications - functioning together as a system. The HA modified non L4 receiver guns would not have received such SA modifications' and as such are a bit hit or miss in function. Like me, you may just have a dog - at least using L4 mags... using a standard .303 ejector and a Zb 39 mag may function in .308 when the .308 L4 mags do not... you'd have to try that out... more parts to obtain and test. Good luck!

[SleepyDoc]

Ok, so if I haven't mentioned it, I am a father (again). I have been on vacation for two weeks since having my newborn daughter and have not been able to get to the range despite having planned to do it, and even having approval from the wife. Something about newborns and not sleeping makes it hard to get motivated to do anything. Anyway, the good news is that since my sleep schedule is so messed up now I was really motivated after hours to take the measurements on the gas ports. They read as follows:

Barrel Port: could not measure
I: 0.098
II: 0.11 on one side, and 0.116 on the other
III: 0.12 and 0.13
IV: 0.145
Gas port to gun: 0.177

I will try more magazines when I get the chance.
Springs still look good when inspecting them, but if anyone has a lead on how to replace the springs to freshen them up I am all ears.

I will try to get her all freshened up and cleaned for a day I get off work early so I can try to make it to the range to give a better update for you all. Since I haven't done anything to it since headspacing it though, the only thing I can really tell you is if I can get it to cycle properly on position IV.

Any other suggestions before I make my range trip are welcome so I can test more things out at the same time.