Bren MKII rescue~

Starting work on my 1943 Inglis MKII Bren.

Nice center section from BRP.
Early MKII with the dual row gas ports on the gas cylinder similar to my MKI.

Winter has to let up sometime!

https://i.imgur.com/Q7g60ul.jpg

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Rear section jigged up , pinned and ready to weld.
This sets the length to factory spec.

Get some good tack welds , remove alignment rail from top then finish welding.


https://i.imgur.com/frbsvjT.jpg

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Welding is more fun than painting a couple bedrooms...........
Burned a couple sticks and roughed in. Fresh eyes to hit the low areas I missed.


https://i.imgur.com/E1WabZP.jpg

https://i.imgur.com/aofycei.jpg

I am happy each time I see an old war horse but back into action. Hate that all the history is turned into so much scrap.

Been a long break since I had play time to work on my MKII.
Long hours at work and home stuff is a lot less fun but pays the bills.

Got around to turning bolt denial pins, machined holes then welded them in place along with the filler welds for the lower frame and carrier denial.

Cooling off on the patio...

https://i.imgur.com/dDA25To.jpg

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Grunt work with quality hand files.
Cleaning up welds so the rear section slides fully on the lower frame. If this binds or does not fully fit correctly welding the next section to it will only make it harder to work correctly IMHO.

Mill smooth, bastard and a with a safe edge (does not cut) makes it a simple job. Once both sections slide on the frame I will face them off, measure OAL then correct for the required dimension on the drawing, then weld. Sharpie lets you know what's rubbing , or not.

https://i.imgur.com/rekFKXY.jpg

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Have sections cut to correct length and ready to weld rear section.....

https://i.imgur.com/8lgAmVW.jpg

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The little details are what makes the build fun.
Selector stop to block the evil FA position.

https://i.imgur.com/51ymYnv.jpg

https://i.imgur.com/MJV7VmG.jpg

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Had some play time and my MKII is now back into a single piece and closer to being back to life.


https://i.imgur.com/V6qYmQq.jpg

https://i.imgur.com/Bsc8OUZ.jpg
https://i.imgur.com/t1ASPbU.jpg

Laborious and slow but nice work. This will pay off too...

On the areas of the receiver where you have welded it back together, have you found that the weld and the areas around the weld have become harder than areas of the receiver that have not been welded?

Quote:

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Originally Posted by Flying10uk

that the weld and the areas around the weld

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We did this quite a bit here at one time and used to see a difference after refinish, blue or parkerizing. Sometimes it would hide and sometimes it would show darker, whatever that meant.

Quote:

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Originally Posted by Flying10uk

On the areas of the receiver where you have welded it back together, have you found that the weld and the areas around the weld have become harder than areas of the receiver that have not been welded?

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Not on several of the receives I have welded back together.
I use ER70-S3 TIG filler rod and it machines as nice ( a tad nicer) than the original receiver metal. You will still typically get a heat line if you blue or park it finish wise. A hot black oxide finish gives it a 100% coverage if that is the goal.


My Bren MKI double dovetail , minimal heat line in the surrounding metal.

https://i.imgur.com/9ynqwAl.jpg

I gather the copper in first lot acts as a heat sink to try and combat any affect on the heat treatment of the parent metal, looks good I gather the selector has to be gated for repetitive and not F/A mode.
I envy you, in the US being able to have things like that.
If I lived there I'd be broke as, but I would have a gaggle of F/A's and suppressed weapons and .........! well the list is endless although I don't think I'd need a Tiger tank!:p

Quote:

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Originally Posted by CINDERS

I don't think I'd need a Tiger tank!

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You know that's a load of shyte, you'd have one...

Quote:

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Originally Posted by CINDERS

the copper

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Keeps the weld from sticking to your jig.

The welding jig helps with alignment and the copper inserts soak up extra welding heat and control any puddle flow into the receiver. I made the main area with a copper insert that can be replaced and the aluminum jog body really transfers heat.

Ideally I like to bevel / angle both parts to weld and weld from the root up for 100% weld coverage with no voids. When I have a large gap to fill I build up the edge on both sides until they meet.


https://i.imgur.com/Ozwi6er.jpg

https://i.imgur.com/iVU9s2H.jpg

https://i.imgur.com/YWDrv1U.jpg


Welding against copper backers usually gives a nice weld but sometimes it needs touched up and I use a long nozzle on my TIG torch.

https://i.imgur.com/zNAGVxl.jpg

Did you use the same jig on this MK2 as you used when you welded the MK1 or are there differences in the receivers, between marks, that prevent the use of the same jig?

I'm thinking that, theoretically, the same jig should be able to be used on the MK1 and MK2 Bren because the upper and lower receivers are interchangeable but what works "theoretically" doesn't always work in practice.

Quote:

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Originally Posted by Flying10uk

Did you use the same jig on this MK2 as you used when you welded the MK1 or are there differences in the receivers, between marks, that prevent the use of the same jig?

I'm thinking that, theoretically, the same jig should be able to be used on the MK1 and MK2 Bren because the upper and lower receivers are interchangeable but what works "theoretically" doesn't always work in practice.

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Same jig.
Its built four of my shooting buds builds and I have five to build myself.

The internal dimensions are the critical ones and the exterior cosmetic. The jig is machined to internal receiver dimensions.

When a receiver is cut it typically moves and gets larger or tighter. Using the jog its easy to get it really close so there is no internal steps from section mismatch.

My MKI internal surface ~

Before~

https://i.imgur.com/hCbXfDF.jpg

https://i.imgur.com/tECO8NT.jpg


After~

https://i.imgur.com/bLOnKt6.jpg

Lovely job.

Killer work week but forced myself to make a little progress on stuff that has to get done. After welding making sure the receiver, lower frame, cocking handle and bolt & carrier travel freely is a must do.

My standard is the "tilt test" for the bolt, carrier and charging handle to travel their full range by tilting the entire receiver back and forth under their own weight.

Now I can blend in the welds and make it pretty.

https://i.imgur.com/r8AfAC2.jpg

https://i.imgur.com/OSUd6yp.jpg

https://i.imgur.com/d12ZdLf.jpg

Needed a firing pin transfer bar for this build but have three more Bren's to build so I made four.

O-1 tool steel and will be hardened to RC C48 this week so I can move on with my build.

Nothing exotic but handle turning and watching the DRO.
Sized a long bar, cut individual pieces and finish milled each.

https://i.imgur.com/XTG5g6K.jpg

https://i.imgur.com/UWntNOK.jpg

https://i.imgur.com/oIQDhov.jpg

https://i.imgur.com/FJSJ8qP.jpg

Very neat work...

Last part to mod for the firing pin transfer bar is drilling a thru hole for a roll pin retainer. You will need a 1/8" carbide drill. The Bren bolts are hard and tough.



https://i.imgur.com/NKnCrWp.jpg
https://i.imgur.com/whH2QlA.jpg

Quote:

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Originally Posted by cal50

carbide drill.

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Yes, I was looking for some of those today, I have to order them.

Piston post milled down to remove auto striker surface and clearance for the new firing pin transfer bar.
I made the post .010" smaller than the transfer pin slot for .005" side clearance.

https://i.imgur.com/0xejLoi.jpg

https://i.imgur.com/qHAUX2q.jpg

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Attached are some views and dimensions of the firing pin transfer bar. This avoids the long firing pin extension and has the added feature of a safety to avoid out of battery firing. The striker can not make contact with the transfer bar unless the bolt is locked exposing the rear face of the bar.
If the bolt does not lock up it will not fire if you pull the trigger.


The only dimension I omitted was a 45 degree chamfer milled on the outside square edges of the bar. This allows it to slide inside the bolt.
.050" X 45 deg. chamfer.

The bolt has radius edges and the transfer bar is square so its for clearance so it slides.


Material is 0-1 heat treated to 48 Rc C
Bren bolt is TOUGH , I used a carbide drill to put the 1/8" diameter hole thru for a roll pin retainer.

https://i.imgur.com/JE7rMBD.jpg

https://i.imgur.com/p6sBuZ8.jpg

https://i.imgur.com/ynA1UsH.jpg

https://i.imgur.com/6GMLNUg.jpg

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Views~

https://i.imgur.com/lfgzcUT.jpg

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https://i.imgur.com/AprasFE.jpg

https://i.imgur.com/aRWzwxQ.jpg

https://i.imgur.com/XXfZY7y.jpg

https://i.imgur.com/q1qJD8T.jpg

ANY machining can't be easy with those parts. Everything in there must be hard.

Yep, quality hardened steel.

Use carbide cutting tools otherwise you will not get far.

Trying to beat the deep freeze coming our way and did some welding in the garage.

Cut and welded a piece of key stock to the bottom of the piston post.
This gets milled down to the same height of the existing disconnector reset section and extends the length.

This will positively reset the disconnector and take that task away from the striker block traveling over it. I will clearance slot the striker so there is less interference / drag on it moving forward and aft over the disconnector.

https://i.imgur.com/GcTUNVF.jpg

Milled down and the last thing to do is cut down a roll pin to put in the bolt body to retain the firing pin transfer bar.
Now moving to the butt section and the final part in the conversion to test fire.
All the heavy lifting stuff is about wrapped up.

https://i.imgur.com/BE7tlLY.jpg

https://i.imgur.com/hlzDlvD.jpg

Final stretch : Springs, striker and guide tubes.



I mod the striker base to clear the disconnector and radius the edges of the disconnector to clear the 5/16" slot x. 055" deep in the striker base. On my MKI build my striker was making contact / dragging over the disconnector. That bleads force from the firing cycle and drag on the striker resetting the disconnector.





Spring guide, pusher and separator are pretty straight forward to make.

My Bren spring tube has a little wobble in it spinning it in the lathe so when I drop my parts in I will watch for any drag or binding and mod as needed.



Striker base mod -



https://i.imgur.com/UsXVUjZ.jpg





Disconnector and striker -



https://i.imgur.com/xKLHzc2.jpg





Clearance -



https://i.imgur.com/odgecZM.jpg



https://i.imgur.com/bFjmgOp.jpg





Parts -





https://i.imgur.com/yuuFKKo.jpg



Getting close to test fire -





https://i.imgur.com/Ha9kCxw.jpg

Nice machine work...

Thank you sir.

Do you guys up north have any source of small Bren parts available ?
I have a stripped spare bolt I want to populate without donating an arm and leg.

Most of the places here are out of various Bren parts and its getting worse.

Quote:

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Originally Posted by cal50

Do you guys up north have any source of small Bren parts available ?

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Those are prohibited in every form up here. I DID know a man with some small parts but trying to ship them south could presently send one to the crowbar hotel... What's worse is...he's a hoarder and probably would claim no actual knowledge of this if you were standing in front of him. So I guess...no...

My MKII was built 20 years before I was born........
Crazy that small parts are treated like a complete rifle.

Quote:

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Originally Posted by cal50

Do you guys up north have any source of small Bren parts available ?

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A few UK militaria dealers may have some of the legal to own (in the UK) small parts that go in the small parts tin, in the tool wallet.

Extractor Set for .303 BREN, All Marks

I think importing them into the US might present a problem...?

No idea but I will check it out.

Does Canada have a lot of 303 surplus ammo or is it gone ??

Quote:

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Originally Posted by cal50

Does Canada have a lot of 303 surplus ammo

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Long gone. Very scarce commodity. We use whatever we can get. IVI made ammo that was excellent and new but good luck finding any. Most use Serbian now, Priv Partizan.

303 ammo is scarce, along with lots of other stuff, lol.
Paying $1 a round for reloadable ammo is cheaper than trying to load it.

I have maybe 100 rounds of Wolf 303 left with three more guns to build so I picked up 500 rounds of this.

https://i.imgur.com/DEIlzgF.jpg

https://i.imgur.com/hImb9QZ.jpg

Defense Industries '42, boxer primed and usually good. They made three years of production during the war. I've used that brass later too. Can't say how well they'll fire, but they either do or don't. Let us know...

Rounded up a block of time to declare victory on my Bren MKII weld up and restoration.


I had a snag in reliable cycling and went down a rabbit hole on spring rates , loading and cycling. Mechanically my gun is stupid smooth in every aspect. It goes together and comes apart without forcing anything. Internals are stupid smooth. My gun has its original early style gas cylinder with the extra row of ports and I know I am losing gas ( not helping me) but after doing the same on my MKI DD I thought this would build the same. I was incorrect.

The rabbit hole of spring loads is an Excel sheet I made with actual spring load rates in Lbs. from three different Bren parts sets with original springs.

https://i.imgur.com/Cw0ab0E.jpg~original

Stock Bren spring rates were measured just off the chamber , mid travel and full travel.
This gave me values of 10.7 lbs closed / 16.9 mid travel / 23.3 lbs full travel.

These were original ( used ) Bren springs and the OAL varied slightly , two were close in length , the other shorter.


The main issue with the spring rate is enough force to consistently strip rounds from a fully loaded magazine , enough force to close and make sure the bolt is locked and enough force to not allow the striker to impact the lower frame. I could not get my MKI running with the McMaster Carr springs and this MKII was no different.

I was at a point that I could load 10 rounds and it would run but loading 25 it would not strip rounds from the mag.
The striker spring is a variable in the spring equation. You need enough spring to light up hard primers and commercial , nothing more.

After a long trial and error I ended up winding two custom springs that match the factory rate VERY closely. My gun will strip rounds from a full mag and chambers rounds and locks the bolt positively.

My Wolf ammo supply is about gone / my testing ammo. I picked up 500 rounds of MKVII


https://i.imgur.com/DEIlzgF.jpg~original

https://i.imgur.com/hImb9QZ.jpg~original


This is brass case & boxer primed BUT the boxer primer is about .005" smaller than standard larger rifle primers. After firing various rounds I put them in a 5C collet and opened up the primer pockets so I can reload them. This ammo will not run in my Bren or a 2nd one.

I opened up the barrel gas hole / exit hole and made a special gas regulator to test. With the ports opened up to .170" the MKVII still will not cycle.
This was tested with the bipod removed and the gas ports closed off with shim stock and a hose clamp. This was also tested in a MKIII with standard gas cylinder and no-go. My gas cylinder is not worn , my gas piston is a new US made part with full diameter with the piston unscrewed so the piston head is close to the barrel gas port.

After stepping back and looking at everything from the beginning I could find nothing wrong and no reason why my gun was not running.
I decided to re-load some 303 ammo in my MKVII brass........BINGO!

https://i.imgur.com/DLpKEYk.jpg~original

Like sh*t thru a goose.
My gun will ALMOST run on #3 gas but #4 its never missed a beat.

I have an opinion that its not the volume of gas but the Bren needs a certain impulse pressure and if its not there its not running.
Plugging gas "leaks" does not increase a weak impulse.

I will open up my test regulator to .180" diameter and test again but I will likely pull and re-load this ammo if I cant get it running safely.

https://i.imgur.com/esSYnWM.jpg~original

https://i.imgur.com/8jsHnRM.jpg~original



Now that I am satisfied its correct and running I can make it pretty but I will likely start welding on my L4 Bren project next.


https://i.imgur.com/am9bWdD.jpg~original



BREN MKII Test Fire - YouTube

Way to go and Thanks for sharing.

Later 42rocker