Bren L4 / .308 build

[cal50]

Looking at the pics I assume that the receiver was cut with a plasma cutter when it was made into a parts kit. Is that, generally how most parts kits are cut, with a plasma cutter, or are some cut with an oxyacetylene cutting torch? Whoever did the cutting of this receiver certainly appears to "have given it some" with the cutting, looking at the pictures posted here.

Our BATFE requires all imported MG receivers cut with a oxy torch with a minimum of material removed in certain areas, at certain angles.
Some importers got creative with saw or plasma cutting then feathering the edge with a torch to make it appear like an oxy torch cut but that runs the risk of them being rejected.

Mine was for sure by the torch.

Its an L4A3.

[cal50]

I am happy to be off this week and cant remember the last Christmas week I had off from work in decades.

Welded the barrel nut section together and the weld shrink was about .012" more than I guesstimated. I was more concerned with keeping the barrel nut surfaces parallel for even contact with the nut. I decided to make a basic tool to cut the front barrel nut surface clean then fit the nut OAL for a nice fit.

The tool I made pilots off the barrel socket driven from a 1/4" socket extension from the rear. The cutting face is .010" larger than the barrel nut diameter. I used the adhesive backed "slip tape" people put on walkways , because I had a roll and everything was closed yesterday. It actually worked out pretty well.
After welding everything stayed pretty straight so I used a Sharpie and colored up the front barrel nut contact area and buzzed it with my Ryobi drill.

After it cleaned up I measured it then put the barrel nut in a 3-jaw chuck with and faced off the front of the nut a couple thousands , test fit then back and forth until it just started to slide in. I switched to valve lapping compound and worked it until the nut throws smoothly and goes in and out correctly.

Its a simple task but I try to get every section right before moving on, its time well spent and avoided compound problems.



Tool~

It slides in from the front , put large diameter in first , slide pilot thru into barrel socket then push in 3/16" dowel pin that drives it.
I stuck a piece of the non-slip tape on the face of it and trimmed it with a razor knife.









Nice and clean~




Perfect fit~




Now that the barrel nut area is finished I can measure the front section , cut and get ready to weld.

[browningautorifle]

Nice work...

[42rocker]

Again, I say VERY NICE WORK!!

Later 42rocker

[cal50]

Sarco....... and I spent a half day getting it fitted and its been interesting.

On mine the extractor relief clearance is clocked about 10 degrees off center when I got it to lock up.



I ended up lapping the hell out of the barrel threads ( the lead or extractor relieve is off ) to get it centered and locked up.

To do so I will require a .022" shim on the barrel face to lock up correctly with contact.



As a sanity check I have a bucked of several factory 303 barrels and all of them install and lock up correctly so its the Sarco barrel.



After getting it fitted I welded the front gas cylinder section on , without surprises.


Strangely , these all fit correctly~






Extractor relief centered , need shim for the gap~









Locked up~









Front section is reunited ~

[42rocker]

Sweet! Were you in my bucket of barrels? LOL

Glad to hear everything is working, or locking for you.

Enjoy the Build

Later 42rocker

[cal50]

Pinned the gas block and pressed a dowel pin in place and milled the front of the barrel for the front sight assy.



Need to pin it and drill the gas hole in the barrel.

[42rocker]

Gas piston moving good? Seeing your work, I'll bet it does, just had to ask, lol.

You are doing a great job after starting out with a mgs type of demill.

Can't wait to see more.

Later 42rocker

[cal50]

Gas piston moving good? Seeing your work, I'll bet it does, just had to ask, lol.

You are doing a great job after starting out with a mgs type of demill.

Can't wait to see more.

Later 42rocker

Like a hot dog down a hallway.........Everything is lining up really well.

[cal50]

Bummed that I have to go back to work tomorrow.

Drilled the barrel gas port and drilled retaining pin hole for front sight assy. in barrel without issue or surprise.
Spent a good hour with hand files and grinder cleaning up the torch cut middle section. Most of the slag is gone but the torch melted metal into the grooves and other areas that makes it a PITA to clean up / out.

After clean up I see my cocking slot closed up in width after being torched. I will straighten it before setting headspace and welding sections together.
I have some big gaps to fill in. They are thin sections and fill in quickly with little filler rod.

The one surprise is a repair or revision section on the front cocking handle stop / retainer. This L4A3 came with a folding cocking handle Vs the unique MKII.
No idea if its a revision to use the standard cocking handle or a repair. Either way its been brazed / soldered in place and if you were unaware and tried welded on it solder or braze really makes a nice show when you light up on it with a welder.


Need to add bolt denial pins in both sides of the barrel socket section before welding the mag section to it to keep BATFE happy.


The factory revision / repair is very well done.

Braze visible on top~




Bottom dovetail visible~




End with braze line visible~




Too bad torch guy cant cut a straight line~




Rear of slot closed up and separated with a parallel & shim.
This will be straightened out before welding sections together.