Another BREN-fan (introduction)

[erik3D]

@SNAFU22
Impressive result!
Did it get a heat treatment after welding to get rid of the built-up stress and to reapply local hardening/tempering?
I guess it must be very difficult to prevent warping after such dramatic repairs.

Here's an improved version of my plungers, I think they are more accurate than the last ones.
(the differences are very subtle though)

Information

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[erik3D]

Here's a computer generated image of my 3D model of a BREN butt handle.
The metal bits of the one I based this model on were marked BSA.

[erik3D]

Empty places filled: the 'barrel nut catch and plunger' are included in the assembly now

[SNAFU22]

Nice work. Warping and shrinking are unavoidable and must be compensated for. I did not anneal the receiver, passing a torch over the welded areas only to help even out how they take finish. I found no mention of any original heat treat. The receiver welds like mild steel.

[erik3D]

Well, one of the reasons I asked was this:

It's a few lines of text in the lower right hand corner of that Mk2/1 receiver drawing.
Sadly some of the text has been cut off earlier, but there's still enough useful information left.
Much depends on how many rounds you are planning to shoot with it I guess.

[SNAFU22]

Thanks erik3D, thats interesting. Next time I have it out, I'll try to scratch those areas and see if they remained hard. I'm guessing C scale, HRC 53 is not that hard. They may be far enough from the cutting and welding to have survived. The welded receiver was easily machined, no hardening. So originally maybe a case hard or surface hardening?

[erik3D]

I've never reloaded .303 Britsh, so I wasn't aware that this calibre was designed to use berdan primer cups with such a large diameter (and thickness!).
The berdan primers I'm to used were for the likes of 7.62x51 and 7.62x39, and a LOT smaller.
No wonder then that the 'bite mark' the BREN ejector makes sits so close to the edge of the primer pocket!
I've redrawn my .303 case model to better show its true dimensions.

Also, given the 0.79 mm base thickness of that primer, it's no wonder those semi-auto conversions need a very powerful striker spring to make things go BOOM.

[erik3D]

Here's a section view of the BREN the instant the ejector hits the cartridge case after firing, unlocking, and extraction.
I've drawn the piston post buffer spring at maximum compression, but I'm not sure exactly when it reaches that position (if ever), and/or for how long it remains being fully compressed.

[erik3D]

Still searching for an angle to show relevant details of the mechanism (maybe for an animation of a firing cycle). It's not easy to find a good one.

Looking at it like this it seems a small miracle those cartridges manage to find their way into the chamber : )

[SNAFU22]

Let me know if there is something I can take a picture of.