Need help with semi auto L4A4

[SleepyDoc]

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 UK 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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[tr63]

It is NOT a sarco barrel. It is an original UK 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 .

[ActionYobbo]

It is NOT a sarco barrel. It is an original UK 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.

[SleepyDoc]

I guess this is my fault for not including more pictures initially. The barrel is as described. original UK, Enfield manufacture.
I was wrong. Never should have trusted my memory. It is in fact a Mk3, converted to L4.
Bolt is also Enfield.

Not ideal to have it close on a 308 no-go, but considering the 7.62 max is the MAX for a 7.62 it is theoretically still safe. I would prefer a tighter chamber and I could have the barrel altered to set the chamber back, but I wanted to try less destructive things first. Something like polishing the chamber. If that or other less destructive methods don't work then I can have the chamber set back and re-check headspace. I will probably need a gunsmith to do the latter for me for safety concerns and so I don't mess up the whole barrel. There is enough room from the receiver to the locking block to do this at present time.

I will try to find some throat erosion gauges or measure some spent brass cases to see if there is excessive expansion. The chamber does appear to have more scratches and irregularities than I remember as is evident on the cases. It is hard to believe that would cause anything, but weirder things have happened.

If anyone else has recommendations on how to polish the chamber or what tools to use, please let me know. Any idea what size of shotgun mop would work best? Is flitz the best to safely polish without taking off too much material? I saw someone use a mop or something with high grit sandpaper, but that seems a little much to me.

If anyone has other ideas I would also like to hear them before going down this rabbit hole.

I can also supply any other information or pictures if it would help someone to make another diagnosis or figure something out.

Thank you all for your help in this matter. I will update you as I make alterations based on your input. Given my terrible schedule right now it might be a bit to get something done, but I will try to keep you all in the loop.