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Thread: Need help with semi auto L4A4

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  1. #1
    Member SleepyDoc's Avatar
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    Need help with semi auto L4A4

    Greetings to you all.
    I have contacted some of you privately trying to gather some of your expert opinion and unfortunately I am still looking for answers. I have an L4A4 bren which since acquiring it has had case head separations. It is a Historic Arms build which I have returned to them and they had it running on Radway Green ammunition. I have been unable to get more than 5 rounds down the pipe before having case head separation or other case ruptures causing a jamming issue. I have tried to headspace the gun to the best of my ability and it will close on a go and no go 308 (to be expected), but will not close on the 7.62x51 max case length gauge. I looked through the instructions that Sarco supplies with their new production barrels to check if the fit is correct and everything seems to be in order regarding correct spacing/gaps and lock up etc.
    I have tried surplus remington from the 60/70s, 70s lake city, new production lake city from 2020, reloads, and all have had issues.
    The gun will not cycle on gas setting two and will sometimes crack cases, but usually not have a separation. On 3 the gun will cycle, but almost guaranteed it will have a case head separation.
    More information, the components are mostly enfield original parts. The barrel is enfield as well as the bolt and carrier if I remember correctly. I don't recall the receiver, but I don't think that matters for this.
    A weird not is when doing a chamber casting following
    Since the gun headspaced correctly I am starting to wonder if the gas system or extraction process is somehow causing a violent extraction.
    If anyone has any information or ideas that could help I would greatly appreciate it. I scanned the forums back through 2015 without much luck.

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  3. #2
    Senior Member WallyG.'s Avatar
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    I am going to suppose that the case separations are being caused by too much friction between the ejecting case and the barrel chamber.

    Have you confirmed that the barrel chamber is within service specifications? Bore erosion at the throat might have widened the bore and the expanding case lip might be deforming when fired to a condition where it's front is wider than its rear - causing too much extraction drag/friction and the resulting neck separation.

    I have over the years obtained several .303 surplus barrels her in the US that look fine but are "shot out" and cause the same separations that you describe, Unfortunately finding a "replacement" .308 barrel will be a challenge. Is your barrel a true/original UKicon .308? Was the gun built specifically for it? Is the bolt an original UK .308 bolt? You would be wanting to try a new barrel to eliminate the variables that the current barrel might be introducing into the equation. If the barrel and bolt are original UK .308 then trying to test other calibers to eliminate possible component issues will be more of a challenge.

    As to gas settings... semi auto's as a general rule require more gas to cycle... compressing the additional striker spring(s) and cycling more steel (striker is a new addition to the internals that are reciprocating). Len typically enlarges the barrel's gas port and also drills out oversized the gas block and one of the adjustment settings in the gas nut. Can you confirm that this has been done? I would not expect the now semi auto gun to cycle completely on the 2nd gas port - especially if the components have not been drilled out oversized to deliver more gas to overcome the new springs and mass of the semi auto internals.

    What solution are you seeking?

    Unless there is something to be done to the parts that you have already, new components will need to be found and substituted and function tested to see if the flaw(s) can be identified and eliminated. Again, this will not be any easy path if your gun was built using original UK .308 parts. They are not easy to find in the US and when found are expensive.

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    Really Senior Member Daan Kemp's Avatar
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    Those cases look rough. The chamber might be causing them to stick.

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    Advisory Panel browningautorifle's Avatar
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    A case separation isn't from excessive gas, it's from an oversize chamber. Excessive gas can rip off a rim however, stuck cases will rip off a rim... I doubt the manufacturer is starting with new barrels and just because they parkerize them and make them look new doesn't help. If your chamber is fat it can rupture too. I had lots of case separations over time with machine guns, all excess headspace issues.
    Regards, Jim

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    Really Senior Member TactAdv's Avatar
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    Quote Originally Posted by browningautorifleicon View Post
    ......just because they parkerize them and make them look new doesn't help.
    Yes. Listen to THIS.

    “Parkerizing” is nothing more than phosphoric acid etching of the metal surface. As it is intended to do it causes microscopic pitting of the smooth surface. Among other things, this in effect causes the surface to become rough and porous, obviously no longer smooth much less polished.

    Parkerizing a barrel chamber is -ALWAYS- a very bad idea!!!

    Fortunately, it is largely reversible and easily fixed by liberal applications of something like FLITZ metal polishing paste, applied by fully coating a rotary mop (I use a cotton shotgun chamber cleaning mop, appropriately sized to the chamber you are working.) and placing the shaft of the mop on an appropriate extension and powering it with a portable hand drill, Dremel tool, etc. Use medium speed and make sure the FLITZ paste never dries out while turning.

    Go CAREFULLY.....you can EASILY remove a .001” of metal quickly!! All you want to accomplish is to polish out the microscopic porosity left from the Parkerizing. It does not take much time to do this.

    Once you have removed the porosity and restored a smoothed, polished finish you will likely find your case sticking issues are resolved.

    You WILL discover you have increased the overall chamber bore dimensionally a very slight amount which SHOULD not be a problem.

    Also.....all this being said above....you did not mention whether or not your .308/7.62 barrel is original military (guaranteed chambered correctly originally), or a new-made aftermarket tube.....where no explicit chambering dimensions are necessarily guaranteed. If new-made I sound almost CERTAINLY expect it to have been cut to SAAMI-spec .308Win chamber dimensions, and NOT to military-spec 7.62x51NATO dimensions, which would easily be a problem as you describe if it was SAAMI cut to minimum chamber dimensions which are ALWAYS intended for bolt-action rifles for maximum accuracy.

    If you have a new-made tube, and you’ve tried the after-Parkerizing Polish to no avail, locate a COMPETENT person who can re-cut the chamber using a proper 7.62NATO reamer.
    -TomH

  8. #6
    Member SleepyDoc's Avatar
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    Sorry for the delay. Very busy. I appreciate all the help and will try to get back to your help as soon as possible.

    As far as I am aware it is all original military. Barrel is marked Enfield. All bolt parts and carrier appear to be Enfield as well. It was originally a converted Mk2 by the UKicon military to an L4 when they were switching over to 7,62x51. After it was cut upon entry into this country it was rewelded by Historic arms. I do not see any aftermarket parts other than the SA conversion parts. I do not have throat erosion gauges to measure and do not know how to measure the rest of the chamber. I gave it my best to headspace the gun with the gauges I have and it seems OK, but I'm sure there are other variables to check as well. Closes completely on 308 go and no go, but will not close on 7.62x51 max gauge.
    I assume the gas ports have been reamed per Len's MO and the gun will not work on setting 2, but will on setting 3. This corroborates that thought as well.
    When I sent the gun back to HA for a look over I think he polished the chamber, but I cannot recall. I do see the rings on the shoulder of the cases which is odd, but I can't imagine this is causing enough sticking. Len had said that he had it running like a sewing machine on Radway Green ammunition (can't find any), but everything else I have tried thus far has not worked. I have not tried steel cased (don't want to), still need to try PRVI x51 and many other European surplus rounds to see if they will work. Too bad everything is out of stock and costs an arm and a leg. Lake city 2020 and other US surplus from the 60s and 70s hasn't worked, nor have my reloads. All rupture.
    I have been waiting for SARCO to get their barrels back in and I will buy one of their parts kits with it to get extra parts to try.
    As far as quick things to check that will not cause much damage and then working up to potentially destroying parts to fix the issue, what are my first options to check out what could be the problem? I could try polishing the chamber, but if anyone has a way to measure the chamber first to see if there is in fact an issue first, I would greatly appreciate hearing how that is done. The cerrosafe I have expands too much and I was told it is not a good surrogate.
    Any input on first steps for checking or fixes would be appreciated. I'm leaning toward trying to polish the chamber first, but I would like to hear everyone's opinion on what would mess up the gun least first. Am I understanding correctly that the South African barrels will not work in the L4? Those are the only ones I can find readily available. Everything else will be aftermarket SARCO barrel.

    What solution are you seeking? - A working firearm that will not have case ruptures.

    Thank you all again for help in this matter. I have been hitting my head against a wall trying to figure out what to do.

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    Really Senior Member tr63's Avatar
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    It should not close on the .308 No go gauge !! Your head space is off !! Sarco .308 barrels are short chambered . Historic Arms rewelded the receiver and did not allow for normal bolt and locking shoulder set back and that why you have incorrect long head space . There are many Historic Arms Bren's with all kinds of problems which head space is one . You need to change the the locking with a large/longer one to correct the head space so that the bolt will not close on the no go gauge and the cases should not separate.

  10. #8
    Member SleepyDoc's Avatar
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    Quote Originally Posted by tr63 View Post
    It should not close on the .308 No go gauge !! Your head space is off !! Sarco .308 barrels are short chambered . Historic Arms rewelded the receiver and did not allow for normal bolt and locking shoulder set back and that why you have incorrect long head space . There are many Historic Arms Bren's with all kinds of problems which head space is one . You need to change the the locking with a large/longer one to correct the head space so that the bolt will not close on the no go gauge and the cases should not separate.
    It is NOT a sarco barrel. It is an original UKicon 7.62x51 which if I'm understanding correctly may still close on 308 no go without issue. It wont close on the 7.62x51 max gauge.

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    Really Senior Member tr63's Avatar
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    Quote Originally Posted by SleepyDoc View Post
    It is NOT a sarco barrel. It is an original UKicon 7.62x51 which if I'm understanding correctly may still close on 308 no go without issue. It wont close on the 7.62x51 max gauge.
    I understand it is not a SARCO barrel , Believe me it should not close on a .308 no-go gauge .

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    Really Senior Member ActionYobbo's Avatar
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    Quote Originally Posted by SleepyDoc View Post
    It is NOT a sarco barrel. It is an original UKicon 7.62x51 which if I'm understanding correctly may still close on 308 no go without issue. It wont close on the 7.62x51 max gauge.
    Thats a sarco barrel. They copied the profile from the South Afrcan barrels which is different from the English barrels. Also who ever populated that barrel cut the lugs of the sight base instead of milling the slots in the barrel because thats easier to do than a bit of milling (lazy lazy lazy)
    I am telling you straight that that is a sarco barrel (American made replacement) but you can have what ever fantasy you want.
    BTW that gun was never a Mk2 as you said but it was a Mk3.
    1ATSR 177AD & 4/3 RNSWR

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