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Bren MkI 308 conversion - Does this work?

Bren 308 Conversion

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#1 Grasshopper

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Posted 25 June 2020 - 10:51 PM

Hi All,

 

Just checking to see if I understand this conversion.  (Ok.  Eye-rolls.  I don't know much about the Bren)

 

1.) Find a South African Bren 308 barrel

2.) Verify the headspace in 308 is reasonable in your gun with your 303 bolt

3.) Install 308 extractor into 303 bolt

4.) Find ZB39 magazine (right next to hen's teeth in isle 3 behind the South African Bren barrel).  Don't load too many rounds.  About 20 rounds.

 

I assume dial down the gas system to low.

 

Is this really ok?  I'd hate to hurt an old Bren.  I have much more 308 lying about than 303 these days.  Thanks to all that can help.

 

Enjoy,

 

Grasshopper


Edited by Grasshopper, 25 June 2020 - 10:52 PM.

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#2 m3bobby

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Posted 26 June 2020 - 03:11 AM

ZB39 mags are quite common in the UK. Can you import mags into the USA? I was paying £8 a mag a few years back (thats about $12 to $15 I think).
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#3 johnsonlmg41

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Posted 26 June 2020 - 07:19 PM

Numrich has barrels

they should headspace with a 303 or 8mm bolt without issues, but you can check it manually by pulling the lower and sliding the bolt into battery on a fired round.

Installing a 308 extractor on a 303 bolt doesnt' sound like a good idea to me, but I've yet to actually try it. 

There is a guy on gunboards selling mags for what I believe to be  a reasonable price, and I just got some more from him this week.

 

Do I think it works?  I have all the parts, but no time currently to run it.  Between the mags that don't fit or hold 308 that well, the bolt that doesn't hold 308 in place because it's way oversize and other issues, it may work?  The question will be how well?  I have a stack of barrels including some MK1 barrels in 308 and a better bolt but it will likely be fall at the earliest.   The best bet would be a complete postie L4A1 that is set up for the proper mags, bolt, and barrel and that should run as well as most MG's  which is maybe 80% for most people.  HTH


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#4 BPinFL

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Posted 27 June 2020 - 06:01 AM

I second Johnsons post.

Maybe it will work, but I don't think the .303 bolt will hold the .308 securely, too much slop, the cartridge will probably not be caught by the extractor. Apex has stripped .308 bolts.

BP


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#5 m3bobby

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Posted 27 June 2020 - 12:52 PM

The South Africans used a .303 block in their conversions but the pressed a bushing into the face. You could look for a SA block or bush a .303 Brit block
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#6 Grasshopper

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Posted 27 June 2020 - 04:17 PM

Hi m3bobby,

 

Do you happen to have a photo of the modified 303 bolt?  Sounds interesting.  I may take this set-up for a test drive Sunday to see if the 303 bolt has a chance.

 

Thanks to all so far,

 

Grasshopper


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#7 johnsonlmg41

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Posted 27 June 2020 - 07:53 PM

I second Johnsons post.

Maybe it will work, but I don't think the .303 bolt will hold the .308 securely, too much slop, the cartridge will probably not be caught by the extractor. Apex has stripped .308 bolts.

BP


I was headed down that path and got the 308 bolt and when comparing all the bolts, the 308 is a different length and thus you would either have to have a new barrel made (shorter or longer I forgot which now?) or as it was designed for the L4, switch out the locking shoulder which has different dimensions to accommodate the 308 bolt.    The SA barrel fit fine in my gun, but when we were checking headspace and how it all looked from the bottom there is what I thought to be a lot of cartridge unsupported at the rear.  My barrel guys didn't think it was a big deal?  I though that ironic since about all they see are match rifles? 

 

I doubt you could press a bushing into the bolt face.....I'd think it would have to be brazed or mechanically attached somehow or it would fly off.   I suppose a guy could mill the sides square and press in a bushing, but the bolt seems very hard?  Anytime I chip a carbide over  3/16"  I panic!


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#8 m3bobby

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Posted 28 June 2020 - 05:48 PM

They were pressed and soldered rather than brazed which I assume was to keep the heat treatment. The face of the bolt was also ground down a little however Ive never seen a figure for how much was removed. I do have a few SA 7.62 guns but never thought to measure the length of the bolt.
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