Another BREN-fan (introduction)

Hi all, I'm new here (well, officially), and I'd like to introduce myself.
I'm a mechanical engineer by profession (for more than thirty-five years, oh dear), and deeply interested in firearms technology for even quite a bit longer.
My interest for the mighty BREN (amongst others) has even taken me to Nottingham quite a few years ago, where I was kindly allowed to fondle serial number 000001 itself.
What a glorious memory...sigh...

For a bit over a year now I 've been working on a highly detailed 3D CAD model of a MkI , purely for my own entertainment and education.
It has been quite a struggle without access to an actual gun, or even proper technical drawings of it.
However, this forum was a GREAT help to me, I've found wonderful nuggets of information here. So thank you very, very much for your generous contributions!

I've uploaded some of the resulting images to the photo gallery on this website, just keeping them for myself seemed such a waste.
If you do have a look, please keep in mind that my model isn't finished yet, and I know it is wrong in some places . But I may have missed some, so if you see any glaring, or even minute errors please do let me know!

Here's an example:
[IMG]https://www.milsurps.com/vbpgimage.p...4&d=1643918527[/IMG]

fingers crossed I inserted it the proper way : )

Thanks again, Cheers!

Erik

Welcome Erik. Some very nice work there! The only error that I can see is the detail around the body locking pin on the right side, a very minor thing. I could send you a couple of photos of that area if you like. What is your model made from?

Thank you Woodsy!
Photographs of details i got wrong are welcome indeed!
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 that I did my best to make it look like a real one : )
There are still some little bits and bobs missing, pins mainly, but most of it is there.
However, a few days ago I stumbled upon a drawing of a Mk2/1 receiver/body here in this forum, and finally I could see the shape and dimensions of the feed ramp, the area around the locking shoulder, and some other, until then, 'grey areas'. Assuming that those details are identical, or at least similar in a MkI I can now correct geometry that I had to improvise.
An early 3D model of that Mk2 body, still in white, is also in my gallery.
Sadly I filled up my allowed number of images rather quickly, so what I have now in my gallery will have to do for now.

I've just filled up my second gallery with images that people here might find interesting enough. Hope you like them!
I've similarly modeled a Russian 56-A-212 (AK47), a Winchester 1893 shotgun, and more, but sadly there's no room for those.

Hi erik3D, very nice. I have the equivalent of a neanderthal's degree in technology so, even though its not a dirt under the fingernails type of job, it looks challenging on another level. Can you animate it? Make certain operations functional? Could you print a realistic model from it?

Sure, those models can be animated, but it takes a LOT of time to generate enough frames (images) for a long enough sequence at a decent resolution.
Only springs are somewhat troublesome, they, like all other parts, are rigid geometry, so for every frame a new spring needs to be created with a slightly different shape.
The models I make have 'real' dimensions (I use engineering-grade CAD software), so printing them at a reduced scale as they are will fail in most cases.
Thin wall thicknesses and details that are already small at full scale won't be printable, even on high-end industrial 3D printers.
Where I live (and in the rest of Europe I believe) printing accurate replicas of real firearms at full scale sadly is illegal.
But 2D images can be nice to look at and useful enough too.

Thanks erik3D, that is too bad that you can't print a scale model to display. Even a solid plastic one? Still, I think your computer skills and artistic talents are impressive. I don't have any experience with virtual guns, but can appreciate the time and work you put in. When the Mk1 was made, a computer the size of a building would not have the power to do what you have.

What I meant was that the 3D models I make are not suitable to be printed (much) smaller that full size.
Printing a scale model would require a thorough redesign to allow for the shortcomings of even the most expensive printers.
It would then no longer be as detailed and accurate as it is now, but it still could be a nice thing to have of course.
But it would be a LOT of work.

I would say that while your drawing is good, it shows a much later, say E serial number prefix onwards Mk1 A Bren. This was a much simplified gun. The progression from true Mk1 to Mk1A took place over 6 stages so far as I recall

Thanks for your info Peter, I very much appreciate criticism like that.

I started my version tracing the line drawing in the background.
I nicked it from the inside cover of my copy of 'The Bren Gun Saga' (1986 edition).
That drawing, I think, is of a really early MkI.
The cuts and curves in front of the body of that version seemed too ambitious to model without proper drawings, so I went for a somewhat later, simpler shape.
Was a bit worried that the profile of the barrel shroud wouldn't be appropriate for a later MkI though.
There are more than enough photographs to be found showing this combination, but apparently that doesn't mean they left the factory like that.
Since you didn't complain about it being wrong, looks like I'm off the hook on that one : )

Now for what's inside, does what I have so far also add up reasonably well?
I know from looking at the Mk2/1 drawing that I found on this forum a few days ago that I need to correct some of my 'guesstimations'.
Relatively minor details, but I seriously aim to model it as accurate and complete as I possibly can.
That thing really is full of surprises if you like digging into mechanical stuff!

[IMG]https://www.milsurps.com/vbpgimage.p...2&d=1643917786[/IMG]
[IMG]https://www.milsurps.com/vbpgimage.p...3&d=1643918180[/IMG]

Pedantic again. The bottom illiustration is not quite correct in reality because you could not have a breech block forward and fully locked and an unfired round in the chamber. In the same was that you could not have the change lever set at SAFE in this mode. Your finger simply could not operate it from A or R to SAFE in the time taken for the breech block to move from the sear to LOCK.

I'd be interested to see how you interpret the cam operation of the barrel nut plunger, its spring and the mag opening cover plunger

But VERY good

Not sure if the Bren is part of this animation suite ...

World of Guns: Gun Disassembly on Steam

Regards,
Doug

@Peter
Thanks!
You cought me there : )
I didn't bother properly setting up the trigger mechanism for the 'instance of firing' position for now, thinking no one would notice anyway.
HA, was I wrong!
Of course I will, but for now I'm concentrating on getting the interaction of the 'feed, fire, and eject' bits right.
An example: that odd plunger that pushes the extractor up, supported by a sloping ramp on the boltcarrier/piston extension, why that ramp?
And that small hump where the extractor rests on by the time the ejector kicks the empty case out, it makes me smile.
One can only figure out the design intent of details like that by carefully moving all the bits and see what happens. So now I know (I think).
A mechanism like this is a treasure trove of tiny, but brilliant engineering jewels, and my aim is to discover them ALL!
Building (or 'reverse engineering' if you will) that thing myself, even if only in a computer, is in my view the best possible way to thoroughly get to know it.
Of course original drawings would have been an enormous time saver, but even largely without those I am getting closer and closer It seems.

Yeah, figuring out those barrel nut and dust cover plungers has been a bit of a problem so far. I've only come across one tiny, fuzzy image of one of them.
Would be great if someone posted some clear photo's and perhaps a few dimensions?

@Badger
Thanks, I've seen it mentioned before but haven't looked at it in detail.
However, even if the BREN is featured in that program, it will be its creator's interpretation.
Good or even excellent as it may be, I prefer to base my own reconstruction on the real thing as much as I possibly can.
It will just take as long as it takes : )

Hi Erik
Some photos attached of my MkI Bren body locking pin detail and as a teaser, my MP5A3 with a couple of accessories. As a classically trained draftsman (55 years ago) I am greatly impressed by your drawing program and your mastery of it!
Attachment 123855Attachment 123856Attachment 123857

Thanks again Woodsy!
From the rounded top it looks to me like your BREN is an older version than the one my model is meant to resemble.
My model is intended to have an MkI* body, so it could perhaps be called an 'MkI modified' following the description in 'The Bren Gun Saga'.
That still doesn't mean my model is correct mind you, but if yours is indeed older it should at least be different in some places.

Attachment 123868

Cheers!
Erik

Erik, my gun is an original 1938 Mk I. Your last photo shows the detail much better and it looks fine.

The points that you have asked about, the cam loaded barrel nut locking plunger v the mag cover plus the ramp to tighten up the extractor have all bee explained in articles regarding the Bren on this very forum.

The ramp tightens up the extractor and positively locks it to the spent/fired case to ensure that the extractor cannot loose its grip immediately after firing and during the violent primary extraction and unlocking. There's nothing gentle here......... The ejection is a pretty violent cycle too. That's why the ejector stakes the rim of the primer, to prevent 'caps-out' which plagued the original ZB .303" trials guns.

During our long years as apprentices, in the classroom, we would try to simulate the violent unlock, extract and eject cycle using strong cable tied to the cocking handle. Alas, we'd never replicate the real thing. Not even 'Big John' Hessle, at 16 years old, 6'4" and built like a brick out-house could replicate it.

The operating cycle...... FIRE, unlock, extract, eject, cock, feed. load, lock - FIRE

With the ejector designed to deform the primer you'd think one should be extra careful when manually ejecting a round that didn't go off.
Never actually heard of an accident that could have been caused by that, manual extraction is of course infinitely less violent, but still...

About "the cam loaded barrel nut locking plunger v the mag cover", I've only found a conversation about how to disassemble those plungers, not a detailed description (or images) of those plungers themselves unfortunately.
There is an enormous amount of wonderful information strewn across all those discussions, finding something specific is not so easy.

I was curious about where exactly the ejector would hit the cartridge case in my model:
Attachment 123959
There appears to be almost 1.45 mm between the impact point and the edge of the primer pocket, so the ejector wouldn't actually touch the primer.
Of course my model cannot be much more than an approximation, in reality it could very well be less of a distance, but not very much less.
Still, with enough force, and given the chisel shape of the ejector, I can imagine it would deform the case enough to locally crimp the primer in place.
It was a long time since I last fired a BREN, I simply cannot remember what those case bottoms looked like. If any of you have a clear photograph of the ejector 'bite' marks on a .303 case I would sure like to see it, so I can check if my geometry comes close.
Cheers,
Erik

Thanks to forum member SNAFU22, who almost a year ago posted a drawing of the Mk2/1 receiver that I stumbled upon only last week, I was finally able to thoroughly check my 'reverse engineered' MkI* body model.
Based on the assumption that functional dimensions did not change between versions (for backward/forward compatibility of major parts), I think that Mk2 drawing should be a valid reference.
To do this comparison I modeled the Mk2/1 body based on the drawing's nominal dimensions plus (or minus) half of the indicated tolerance.
Some dimensions were difficult to read, especially numbers 8 and 3, 5 and 6, but all in all that drawing was a fantastic source of information.
Turns out that on the whole my interpretation was pretty much spot on (yay!)
... Except for the all important location of the locking shoulder seat (bummer!).
Even though my model is merely intended for documentation/illustration purposes only, this particular dislocation is way too much to my liking (ca 0.92 mm hor, 0.33 mm vert), so I'll fix that.
There still are a few grey areas to be filled in for completeness, and lots of questions about certain design features (why the strange lateral offset of the return spring?), but I am very happy about the progress made so far.
Thanks again to all who (unknowingly) contributed, especially Peter Laidler of course, and SNAFU22 for that wonderful Mk2 drawing!

Here's an image showing that comparison: Top (section A-A) is the Mk2/1, Bottom (section B-B) is my MkI* model (dimensions in mm's)
Attachment 123972

Cheers!

Erik

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.......

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.

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

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

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.

https://www.milsurps.com/images/impo...Bren1png-1.jpg

https://www.milsurps.com/images/impo...printpng-1.jpg

https://www.milsurps.com/images/impo...printpng-1.jpg

@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:
Attachment 124029
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.
Attachment 124030

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?

@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?

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 : )
Attachment 124107

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.
Attachment 124196

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:
Attachment 124197

In 3D that comparison looks like this:
Attachment 124198

Hope some of you find these images useful.

Cheers!
Erik

For reference, an Enfield Made Mk1 in 1943 wouldn’t be marked as such on the right side.

Thank you sir!

I was inspired by the drawings on pages 60 (fig 57) and 75 (fig 78) of the 1986 edition of 'The Bren Gun Saga' that show those markings on the right hand side.
But those marking could well be merely intended for identifying the illustrated version.
I did come across a series of photographs of a cut-up 1942 Enfield MkI (where one could see both sides) that didn't have those markings.
Images that show a close-up of the right hand side with that marking (and no Inglis, or other markings in view) must be from other makers then. Older Enfield MkI's do seem to have them, so it's easy to get confused.

Anything else not right that you've noticed?
Did 1943 Enfields have drilled-through magazine catch levers (instead of the closed one I used) for instance?
I'd be grateful for any old bit of information, however minute.
Thanks.

Erik

Here's a drawing showing the moment the breech block is fully unlocked, but still hasn't begun moving backwards.
Attachment 124480
The leverage provided by the tilting motion of the breech block has loosened the cartridge case from the chamber walls.
It could well be that the heavy piston post spring is already compressed at this stage, but I imagine the force needed for unlocking the breech block could well be less than for accelerating it to the considerable speed of the piston assembly.

One really has to look at it from all sides to appreciate how clever those designers were who made this.
It's not easy to find a single angle that clearly shows how these tightly packed components work together. Taking parts out, in this case the barrel, can help a bit but isn't ideal.

Shame about the empty holes for the barrel nut and dust cover plungers.
Usable images showing what they look like in detail are proving difficult to find.
Attachment 124597Attachment 124596

Pics might help you model the detent pins.

https://www.milsurps.com/images/impo...P2270905-1.jpg

https://www.milsurps.com/images/impo...P2270906-1.jpg

https://www.milsurps.com/images/impo...P2270908-1.jpg

https://www.milsurps.com/images/impo...P2270912-1.jpg

https://www.milsurps.com/images/impo...P2270915-1.jpg

https://www.milsurps.com/images/impo...P2270917-1.jpg

Thank you very much again SNAFU22!

You're welcome, This is what I had to work with.

https://www.milsurps.com/images/impo...022/02/2-1.jpg

Eeeeeuw, what a horrific sight!
Is that the same gun as in your last photo?
That would be quite an accomplishment!

About those plungers: these should come reasonably close (I hope)

Attachment 124628

Nice job on the pins. Yes same gun.


https://www.milsurps.com/images/impo...PA280430-1.jpg


https://www.milsurps.com/images/impo...ren8of12-1.jpg

@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)

Attachment 124631

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.

Attachment 124632

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

Attachment 124638

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.

Well, one of the reasons I asked was this:
Attachment 124643
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.

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?

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.
Attachment 124735
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.

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.
Attachment 124755

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.
Attachment 124768
Looking at it like this it seems a small miracle those cartridges manage to find their way into the chamber : )

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

3D Animation Facts: How a Bren Gun works - YouTube

Bren gun: full disassembly assembly - YouTube

Nice animations @SNAFU22, but what I am thinking of would be much more in detail than these.
The way the extractor is tightened by the boltcarrier during unlocking for instance, that's quite unique for the Bren as far as I know.
And something I certainly didn't notice while handling, shooting, and (dis)assembling one.
A LOT of work though, animations like that!

What I would very much like to see clear pictures of is the 'Ejection Opening Cover Catch'.
Don't know if it's easy to remove, hope it is.
The one I've modeled now would probably work, but it isn't based on solid, detailed information.
Thanks in advance for (hopefully) taking the trouble SNAFU22 !

Seems like there is always one more pic I should take. A stop screw in the lower keeps the the latch pin from lining up with a hole in the lower. Remove the screw, align the holes, and push the pin out. Can you "stamp" the E in the D on your latch?

https://www.milsurps.com/images/impo...P3120919-1.jpg

https://www.milsurps.com/images/impo...P3120920-1.jpg

https://www.milsurps.com/images/impo...P3120921-1.jpg

https://www.milsurps.com/images/impo...P3120922-1.jpg

https://www.milsurps.com/images/impo...P3120925-1.jpg

https://www.milsurps.com/images/impo...P3120926-1.jpg

https://www.milsurps.com/images/impo...P3120927-1.jpg

https://www.milsurps.com/images/impo...P3120930-1.jpg

@SNAFU22 Thank you very much for those photo's !
They are of a newer version of the catch than the more curved Mk1 model, but functionally they should be very similar.
There is a small vertical projection, or pin, in the sliding cover itself that I haven't seen before.
Haven't got a clue what that is for, but I assume it is some kind of improvement.

'Stamping' text or symbols on/in 3D-models is no problem at all.
Hey, I could do some nice scroll engraving with gold inlays and a hunting scene on the sides of a Bren, there's plenty room for it : )
Here's an example of a roll engraving on an old Smith&Wesson revolver I've modeled recently:
Attachment 124808
For this I just need a good image, from a photograph for instance, so I can convert it to 3D geometry.

Here's a 2D drawing of a fully compressed Bren recoil buffer.
The receiver (or body) is also in its rearmost position.
(the section plane is in the centre of the buffer, not in the centre of the boltcarrier, they are offset to each other)
It appears the bolt (or breech block) is stopped by the lower receiver itself, not by the buffer.
Attachment 124809

I've found some old photo's of a visit to Nottingham, many years ago.
Brings back memories.
Here's one of them:

Attachment 133016

(I photographed the print with a digital camera, so the quality isn't too great)

Cheers!

I'm afraid I have to confess that back then to me this one was much more interesting:

Attachment 133017

Attachment 133018

Sorry 'bout that :D

There were several variations of the catch, cover, ejection opening. The last version was one of the last modifications for the L4 gun. I seem to recall that it had a longer 'catch' part so it would engage and hold open a few mm's sooner.