Changing Mk1 buttstock for Mk4

I have a semi auto L4 rewelded by Historic Arms.
It currently has a Mk1 buttstock. I have bought a Mk4 buttstock and a Mk2 combination tool to remove the current one.
Can I use the same mounting hardware or do I have to find the Mk2 hardware?

?......... What do you call 'mounting hardware' You can simply 'mount' the new L4 butt onto the Mk1 type return spring tube quite easily although you might have to fit the woodwork a tad to get a close fit onto the butt socket.

But you will also need a new:
NUT, return spring tube, BE 4123 or 9688 to hold the butt onto the gun.

If the L4 type butt came to you as an assembly, then all is well. But if not, you;ll also need a new:
WASHER, return spring tube BE 4148
PLATE, butt BE9667
SPRING, detent BE4145
BRACKET, butt assembly plus 4x screws.

I dare say that if you do need any of these parts, just say so and other forumers might be able to help out.

Just as a matter of interest, the L4 gun butt plates were modified to incorporate a loop at the top of the butt plate to enable better use of the sling AND use of the later/better L7 GPMG sling

Thanks Peter,
The new buttstock came as an assembly, but I only have the Mk1 return spring tube and nut etc that is currently holding on the existing buttstock.

The Mk4/L4 type butt will fit over the Mk1 ret spg tube but you might need to clear a very small amount of wood inside that might foul the Mk1 ret spg tube. But just a very small bit...... Look inside the Mk4 butt to make sure because the washer usually comes as part of the assembly and is pressed inside. So it MIGHT be there but you ain't noticed it*. Then you only need a new nut. Either type will fit/interchangeable.

Just a tip.......... Assemble the butt to the butt slide WITHOUT the butt plate and detent spring and when it's tight and the cocking handle operates freely (might need a bit of clearance in the wood too) only THEN assemble the detent spring and butt plate.

While you're there, notice that the ret spg tube hole down the butt and the corresponding hole in the butt plate are offset to the left by a few mm's. This is another bit of the remarkable design of the magnificent Bren. It's to allow the cocking handle slide to embed itself into the butt.

* you can always tell for certain with a Bren and a No1/4/5 by hitting the ridge area with a long steel screwdriver. If it sounds soft and 'thuddy' then the washer is missing. A good solid metallic sound and it's there!

Thanks for the additional information Peter. I took the butt plate and spring off and, indeed, the washer is fixed in place inside the hole. I just need to source a nut now. Non of the usual online parts retailers in the USA have any in stock at the moment. Is there any way of making the Mark1 nut fit, if I cannot source either of the newer versions?

Give it a few days and I'm sure one of the UK Bren fiends will be able to help. On the other hand, these things regularly appear on that auction site. A Mk1 nut thinggy will screw on but it'll need to be machined and then you'll need the cup bit and then it'll protrude out of.............. Just get the real McCoy........

I think I have found a nut from Sarco. They described it as a Bren Mark2 Buttstock Retainer! but when I asked them if that was actually the Return Spring Tube Nut, and described what it was for, they confirmed that it was, indeed, said nut.
I am trying to convert to the L4 configuration that Capt. Laidler suggested when I posted a picture of my Bren, No4, No5 and Enfield Mk2 revolver a few weeks ago. I have already replaced the bipod for a Mk1, and need to get a newer carrying handle after I fit the new buttstock, and then I will call it a day. The flash hider on my barrel is not the L1A1 style though and seems to be a custom made muzzle break. Maybe, one day, I can get a correct spare barrel too. As these guns are rewelded from numerous kits and then are converted to semi-auto, I'm not too bothered about it being overly authentic though.

The barrel in the picture you have in your profile folder is a South African .308... it employs the standard muzzle brake design commonly found on various FAL rifles of the period. The smith who set up your gun has managed to get it to feed from the UK .308 magazines... but is using the SA barrel (it does not require a 7.62 bolt etc. that a complete UK military conversion would require).

Thanks for the new information, all very interesting. As these guns are welded up from kits, I expect that many hybrid parts are used as a matter of course. The receiver is marked as an Inglis MkII from 1943 then restamped (badly) as an L4A4 with 1959!!
I have attached more photos of the receiver, barrel and bolt/carrier.

Is that a complete new section of body? I'm looking at the distinct vertical ridge down from the mag catch axis pin. The original INGLIS/date would be on a surface level with the BREN Mk2 marking