Bren MKII rescue~

[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.

[cal50]

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.

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~






After~

[Flying10uk]

Lovely job.

[cal50]

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.

[cal50]

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.

[browningautorifle]

Very neat work...

[cal50]

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.

[browningautorifle]

carbide drill.

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

[cal50]

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.





---------- Post added at 03:59 PM ---------- Previous post was at 03:58 PM ----------

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.















---------- Post added at 04:00 PM ---------- Previous post was at 03:59 PM ----------

Views~

[browningautorifle]

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