Another BREN-fan (introduction)

[Peter Laidler]

The ejector doesn't strike the cartridge cap. It strikes and deforms the cartridge case JUST above the primer pocket. This is just sufficient to firmly hold the primer in place during the harsh EJECTION process. This is not the ony thing that prevents 'caps-out' as the yrials report suggests.

The deformation of the primer by the heavy oval striker or firing pin also very effectively ensures that its ovality spreads - displaces the primer material towards the top and bottom edges of the pocket. The primer is well sealed.

To be honest, in my dealings with Bren guns, Mk2's in the UK and Mk3's in Malaya, caps-out was never a problem of any consequence to us. Clever chaps those Czech designers.......

[mrclark303]

Great insights into Bren ejection there Peter...

The last time my local (ex RAF airfield) gun butts were dug out, the amount of WW2 .303 cases that came out was considerable. (We assume they buried the spent brass in front of the butts) the Bren struck cases where obvious, compared to the Enfield.

Re the Czech fireams design, they really do have a flair for it, even under the Soviet jackboot, they shunned the ambiguous AK47 and designed the fascinating and compact striker fired Vz58.

The thing I really find intriguing, is the Soviets didn't insist it was designed to use AK magazines.

[MGMike]

If by "what is your model made from" you mean a real material, there is nothing other than zero's and ones in it, because it only exists in my computer. It is a CAD model tIfhat I did my best to make it look like a real one : )

Incredible! I was born too soon.

M

[MGMike]

Somewhere is the cobwebs of my memory I remember reading that the Czechs experienced some problems with "caps-out", so naturally the Holek brothers --being very thorough-- worked in a solution, whether it was still needed or not.

My belief is that it was more a defect in ammunition than in the gun. I had a similar mishap in a Johnson LMG with some late-'50s German .30M2 ammunition. A primer popped out and lodged firmly beneath the sear, disabling the gun! The gun had to be taken into the shop and disassembled to clear it. The primers apparently were not adequately staked.

Peter: Glad you're well. You won't recall but we met years ago at the reference library at Shrivenham.

M

[SNAFU22]

Hi erik3D, here is another print of the mag well. The pdf. I have of the receiver print has much better resolution than this. If you still need more dimensions, let me know. I could get them or I could email you the print.

[erik3D]

@SNAFU22
I've used a 4 MB .png of 2376x1836 pixels that I downloaded from your answer in the 'MK 1 Cycling issues' thread. A careful cleaning session in Photoshop did much to improve it, but there are still some blotches that I can't really read.
Here's a similar crop after treatment:

Is your original .pdf much better that that?
If so, I'd sure like to have it!

The other drawing crop you've uploaded is one of the few drawing fragments I've found here when I started this 'project'.
It looks like a photograph of a much clearer drawing, and of a slightly different version.
If only there were more pieces of that particular drawing to be found.
Better still of course would be a crisp, undamaged, high rez drawing of an MkI, but it seems none are available.

Here's a drawing with some of the dimensions I've derived from your Mk2/1 drawing (in mm's), combined with other parts I already had.
I've marked in red two areas where I think there should be some clearance to make things work properly.
Looks like the bolt I drew is a little bit too long, and it is pushed up a tiny bit too high by the bolt carrier.
This design doesn't appear to allow for much deviation from the theoretical dimensions of its essential components!
In practice that can only mean that, apart from the barrel and matching locking shoulder, you'd have to be very careful selecting parts (upper receiver, boltcarrier, bolt) to make sure they work together as intended.

[AmEngRifles]

Great work Erik3D.

I am curious, once done, can this type of drawing be put into a CNC Milling station and run to produce a finished product? What once would have been laborious on the old fashioned mills, would possible be much more cost effective on modern multi axis milling stations? I am no engineer or machinist.

Also, would the MOD or the Royal Armouries or some other source within the UK actually still posses all the original drawings for the Bren? Although they may not be available for coping by individuals?

[erik3D]

@AmEngRifles
If you want to fabricate a part on a specific CNC machine you'll have to design that part from the beginning to be compatible with that machine.
These sublime devices are not magic wands that can spit out any random shape or form, they have their limitations too.
Being designed almost 100 years ago, we can be absolutely certain that the BREN was not intended to be produced using CNC machines.
Besides, I would expect the cost per unit for producing just a handful of parts this way, as opposed to thousands and thousands, to still be horrendously high.
And with thousands and thousands of perfectly functional BRENs being destroyed because nobody wants them anymore, why bother?

[erik3D]

Here's a drawing that should be accurate enough to be used for illustrating a question or perhaps an answer about the BREN design.
Feel free to edit it to your hearts delight in your favorite painting program : )

[erik3D]

It's a pity that original Mk1 drawings still do not seem to be available to the general public.
Making do by combining information that is may fill that void to some extend.
I've superimposed a (fragment of a) drawing of the original Mk1 over the Mk2/1 drawing that SNAFU22 posted to make visible the differences between them.
(black lines are Mk2/1, red lines are Mk1 double dovetail)
It looks like the overall contour didn't change much; most of the lines overlap or deviate only a little, mostly due to folds in the scanned drawings.


This certainly helps to validate my assumption that a drawing of an Mk2 could well be used to reconstruct a drawing of an Mk1, which I did here:


In 3D that comparison looks like this:


Hope some of you find these images useful.

Cheers!
Erik