My .308/7.62mm fullauto conversion- Plug & Play Success!!

[AmEngRifles]

OK, had a little time today to spend with my Bren. Specifically, my South African .308 barrel and my Bren.

The barrel has the black synthetic ( thought it was just a painted wooden handle originally) handle, with the MkI profile, meaning it has the nice swell, not the tube type, like the late model Bren handles. It also has the standard style Bren front sight. Don’t ask me WHY I thought I may have an Uzi style front sight!? Guess because I pulled my Uzi out a short time before responding to the inquiry. My mind sure can mix up facts. Anyway, going to just keep this barrel and be happy. The bore is very nice and that is what counts. Mostly.

I tried it on the Mk III, PG. locked down easily. Bolt slid home nicely, on a live cartridge. Had a very small amount of play. Probably any is too much? No gauges at this time. Soon.

Tried on the HA MkI. Lever did NOT lock down with hand pressure. The locking portion of the lever, which grabs the underside of the receiver so it stays put, was about 1/8” or less away from locking. Could have taken a rubber mallet to it, but I figured I would NEVER get it unlocked if I did that. Might should try the MkIII locking lever in the MkI when using the SA barrel. Haven’t tried that yet.

Same with the HA L4. The SA barrel lock nut gets very close to locking down,, but I’d about 1/16” away from doing so. Again, refrained from taking a mallet to lock the lever, knowing the pry forces to get it back open would probably lead to a minimum of scratching of the receiver. Just let it be. Will try to secure a few alternative locking piece. I believe BRP carries an assortment. Will try the MkIII lever first since the barrel goes right in the Project Gun with little effort.

What I did notice in my less than scientific trials, was on both the HA rifles, with extractors removed ( as well as firing pins), the bolts would JUST click closed with the slightest of resistance, when the bolt locks up against the locking shoulder and a round was inthe chamber. Like I said, not scientific, but I was feeling better about tolerances in the two HA Guns. One is in .303, one is an L4.

So that is where things stand. I will try the locking nut switch first, then probably order .7.62 gauges, then if all feels good, maybe try one of the .303s in 7.62. Still need to get some brass sheet and silver solder and make the modification to a few ZB mags.

With multiple projects, little range time and a confusing array of issues to resolve, I am lucky to be making any forward progress at all

I need some material to restrict full compression of the mag spring in the L4 mag and I will only expect to load no more than 27 rounds. I wish I could nest a spiral spring along with the flat leaf spring, even if not the same full length, and give the follower a little extra push, especially for the last few rounds or so. Don’t think that is the right way though, as a spring as long as the original would take up too much space in compression. And a short one does not do much by time the flat spring is fully extended in a nearly empty mag. Expanding block of foam? Rubber grommets? Or just put a solid block of something in the base of the mag to give the ole flat spring a little more push near the end?? Ideas?

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My Mk II is a Wise Lite build and I have 5 .303 barrels that all fit the receiver using the same barrel nut and head space correctly . The GunParts, South African .308 barrel as noted earlier had no problem with barrel nut fit or head spacing . I have head the receivers rewelded by HA and some others may have mag. wells too long in length, and the locking shoulders were reworked to get the head space right . How do your spare barrels fit for your HA receiver reweld ? My Mk II was built using IMA cut receiver that had the barrel nut socket intact and there was no issue with the locking nut fitting correctly .

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I think I will attempt this caliber conversion on my SMG-built Mark II Bren gun.

Nice to see barrels finally available for .308. They're expensive, but well worth it in the long-run. I've already successfully converted a TNW MG-34 to .308 and have fired about 1k rounds down it without much issue so far outside of the usual teething issues seen in the TNW MG-34 semi-auto conversion. I will also have to acquire some ZB-39 mags.

What headspace gauges are people using to headspace their guns in .308? Will a Forster set work well?

[tr63]

I think I will attempt this caliber conversion on my SMG-built Mark II Bren gun.

Nice to see barrels finally available for .308. They're expensive, but well worth it in the long-run. I've already successfully converted a TNW MG-34 to .308 and have fired about 1k rounds down it without much issue so far outside of the usual teething issues seen in the TNW MG-34 semi-auto conversion. I will also have to acquire some ZB-39 mags.

What headspace gauges are people using to headspace their guns in .308? Will a Forster set work well?

Yes a Forster head space gauge set will work . The go gauge at i.630 is what you are looking for the bolt to close on . And the 1.634 gauge is the no go for the bolt not to close on . See JOE H's information listed in this tread for the correct way to head space the South AFRICAN .308 barrel for use in a Bren chambered in .303 .

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Yes a Forster head space gauge set will work . The go gauge at i.630 is what you are looking for the bolt to close on . And the 1.634 gauge is the no go for the bolt not to close on . See JOE H's information listed in this tread for the correct way to head space the South AFRICAN .308 barrel for use in a Bren chambered in .303 .

OK, ordered a set of Forster 7.62 NATO sets at Brownells and the. 308 barrel from Numrich. Here's hoping that the barrel fits with my existing barrel collar and headspaces correctly without any issues.

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Got my SA barrel and it seems like the bolt is able to barely close on a 7.62 Field gauge.

Looks like I should probably swap out the locking shoulder for a bigger one assuming mine isn't already the largest shoulder installed in the gun already. How well-torqued is the screw that locks the locking shoulder in the receiver usually? Seems like it should be just a matter of unscrewing it, counterclockwise like is usual for screws, but just want to confirm that it's not some weird clockwise-to-unlock screw.

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The locking shoulder screw is staked in . You can see it when you look at the screw inside the receiver . You must have a very well fitting large tip screw driver the receiver should be clamped in a padded vice and be very careful in the way you try to move the screw . If you destroy the screw you can get a replacement from BRP or GUNPARTSCORP . How is the head space you not have with the existing barrel ? Maybe JOE H can offer some advice as to how best to remove the screw .

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I haven't checked the headspace of the gun with the original .303 + bolt combination, but I imagine it should be good as I've fired hundreds of rounds through it already and don't have any signs of bulged cases or torn heads. This is Greek HXP .303 I've fired through it, along with some Prvi-cased reloads I've tested.

I'm thinking I probably shouldn't mess with the locking shoulder if I want to maintain the .303 British headspace with the bolt and barrel that was originally supplied with the gun from SMG.

Would a better solution be to utilize the spare L4 bolt I have for 7.62 NATO and do the semi auto cuts for the side of the bolt by milling the channels away, and then shaving the bolt face and/or the locking shoulder surface a few millimeters in order to fit it into my gun and do it slowly until perfect headspace is achieved? I know that the L4 bolt is slightly longer than the .303 British bolt by 2-3mm, but it would also have the added advantage of having the cartridge head recess on the bolt face be perfectly sized for the 7.62 NATO round.

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Some one above my pay grade will have to chime in on the L4 bolt use .

[Joe H]

Syntax,

If it is correctly head-spaced it should not close on a Field Gage. It should close on a GO gage which is shorter and not close on a NO-GO. The Field Gage is longer than both the GO & NO GO and is used for checking existing firearms for excessive headspace. If it closed on a Field Gage it should not be fired.

Use only the bolt for checking HS no springs or extractor. The bolt is extremely hard, I wouldn't mess with it.

The 7.62 nato headspace is looser than the .308 Win.

The locking shoulder screw is staked in an may require a pencil grinder to relieve the punches for removal. It is a right hand thread.

I'm not sure you have any problem.
Joe