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Bren MkI 308 conversion - Does this work?


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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
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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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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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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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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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  • 1 year later...

Hi All,

FWIW, I gave the SA 308 barrel a try on Friday. Headspace was generous but not too bad. a 1.634 gauge would close if you leaned on things. As luck would have it I misplaced the 7.62 extractor so I just gave it a go in semi with the 303 extractor. It fed and cycled dummy rounds just fine so off to the range.

I started with a few powder puff loads of 12 gr. of Unique. I didn't expect it to cycle. I did want to check feed. It did what one would expect. Point of impact at 50 yards was essentially unchanged and it was a wonderful single shot MG.

I'd figured out how to do some minor body and fender work on the magazines so they would lock in nicely. I had no feeding issues other than from time to time it left a round in the magazine. I just started loading an empty case in the magazine before the live rounds. No issues other than the left over last round about 50% of the time.

The full load 308 rounds fed, fired, and extracted in semi except for one time. I only fired about 40 rounds. It was fun and got it sighted in.

Brought it home. All looked good. 308 brass looks better than my 303 brass for shoulder movement per my Wilson gauges.

Then I found my 7.62 extractor :) . Sunday I hope to get the Bren back out with the 7.62 extractor. The empty casings hook quite well under the extractor. I'll report back after the next range trip. If I remember I'll get a video.

Enjoy,

Grasshopper

Edited by Grasshopper
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  • 2 weeks later...

Hi All,

 

It's late. I'll be brief. When I figure out what is going on I'll adjust the post.

 

1.) The magazines I have fit the gun good. The 308 round is too short. If the rounds are toward the rear of the magazine (and stay there) it runs great. If the rounds shift forward in the magazine the gun stops feeding.

2.) The shoulders on the cases are forward a bit. Not as bad as my 303. The 303's are running about .025" forward (subject of another post). The .308's are about .010" forward based on a Wilson shoulder position gauge. I didn't want to mess with the locking piece as the gun is a factory 1940. Turns out (when I had the ejector out) the screw holding the locking piece in place was loose. Have new locking pieces on order to try to tighten things up a bit.

3.) Weird things - Cocking/charging handle wants to reciprocate. The gun is a MKI. The gun doubles on semi unless I hold the cocking handle flat with the side of the receiver. Not sure what is going on. This happened with the 303 extractor (shooting 308) and the 7.62 extractor (shooting 308). I need to set-up the gun in 303 again to see if this is something that just happened to an 81 year old spring on the cocking handle or ?

 

3.) Update - For comparison, I bought a new cocking assembly. The spring in the original fold-out cocking handle has died. The new folding handle snaps into place smartly. I'll be taking the original apart to see what happened to the spring very soon. Seems this part of the mystery has been solved.

 

4.) If I take a fired 308 casing and neck size only, the brass drops right into the chamber with the barrel off the gun. I can't get it to go into the chamber with the barrel on the gun having the bolt drive it to battery. Funny thing is a fully resized case will feed from the magazine even w/o a bullet. Something is not aligned right. I need to do more work.

 

So far I'd have to say it is not worth the trouble to attempt the caliber conversion in this manner. (Spend your money on more 303 and not a barrel and mags!) I certainly appreciate the comments made from other members and have been pretty much spot-on.

 

Take care,

 

Grasshopper

Edited by Grasshopper
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