L4A3 (308) completion help

[Joe H]

Brit & Peter ( and all the other guys across the pond),

Attached is a pic of the L4A3 de-mills that have now become available in the US. These are the only L4 kits available. Also a pic of the previously available Mk I & II MGS demills.

You can see the barrel socket area is gone in the L4A3. Alterego welded in the barrel socket from the MGS demill into the L4A3. The problem is that the L4A3 kits do not have a barrel since barrels cannot be imported into the US.

Once Alterego got the weld up done he had a L4A3 body but since I think he used a Mk I barrel socket the exterior contours would not match the L4A3 in the barrel socket area. Everything internally should be the same as the L4A3.

Modified the bolt stops?? Maybe Peter can answer. I know C310pilot knows since he stated with a Mk II and completely made it into a L4A3.



Joe

[Peter Laidler]

Jeeeees! See what you mean......... Notice that the gas blast shield is also modified too.

The breech block stops aren't modified for the L4 guns. A .303" breech block might fit an L4 gun without a barrel but once a barrel is fitted, the extended feed horns will foul the top part of the 762 barrel and won't allow it to lock up into place. No lock up on a Bren, cannot fire.

[Joe H]

Alterego,

I rebuilt one of the MK II MGS demills into a semi. The location of the barrel socket gave in a lot of grief. I had the piece set too far back so that bolt was hitting the stops before setting on the headspace gage. I thought I had it set right but I had to grind the LS back. Luckily I discovered the bolt was on the stops and I had inadvertently built .040" into my head-space before I fired it. The moral of the story is that if you are using the MGS barrel socket section be sure to check that is in the correct location relative to rest of the receiver. Probably best to check it with an original receiver drawing. Just my 2 cents from experience. I would think either bolt should work without the barrel.

Joe

[Brit plumber]

Are these A3s some of the Ex Irish stock? It's a shame the numbers will have been destroyed as I'd liked to have added these to my list.

[Peter Laidler]

Oh, no........ not MORE Ex Irish stuff........

[ZGB]

I think they were originaly sourced from PAK. Thats where the last batch of L4A3's came from that have recently been on the european scene.

[alterego]

Ok, dug into this a bit more. It just didn't make sense to me that they would have broached/shaped the forward bolt stops in the conversion process, just would have been too complex/time consuming. It seem that the socket to the locking shoulder is too short by ~0.040". So cut it in half and reweld time!

Is there anywhere original drawings can be had?

[Joe H]

Alterego,

The dimension you need is 5.389" (136.88mm) from the rear face of the barrel nut recess to the center of the magazine catch pin.

See attached PDF.

Discussion here:

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Joe

Attachment 70398

[Peter Laidler]

Joe, can I make a suggestion? What about putting down the measurement/distance of that distance WITH THE mag catch axis pin IN PLACE. I.e. from the rear of the pin to the rear face of the barrel nut recess. That way it's an easier method of measuring the distance while using a vernier caliper.

I realise that it is also pretty obvious to home builders but what Joe has mentioned is probably the most important measurement you will need. It's also pretty obvious but most important to remember that when you are clamping up, that as well as being the exact distance (above - thread 18) the barrel bearing surface must be dead square to the body both vertically and longitudinally.

Great thread and us Englishers are learning a lot about the parts kit Brens in the US

[Joe H]

Peter,

The measurement you are referring to is 5.467" (138.86mm). Assuming everything is lined up the real challenge is the control/estimation of the weld shrinkage in the joints. this could be .015" per joint.

The other demill type, highly desirable, and sometimes available here is the IO. Pic below. These were imported years ago but the ATF will no longer allow importation with the IO demill cuts. And barrels can no longer be imported. If you carefully look at the location of the demill cuts from IO to MGS to Sarco you can see the increasing difficulty of rebuilding.

The front & rear cuts of the IO are no problem. Headspace is set with the middle cut weld up.

The middle cut in the MGS is through the locking shoulder area. The front cut is through the barrel socket. Issues- locking shoulder slot rebuild, length of the slot for the mag catch, bolt stops location, barrel socket rebuild

The Sarco IMO is probably worse than the MGS as you need a donor or newly machined barrel socket.

Joe