Double "Rat's Tail Springs"

I am currently doing a little restoration work on a couple of my Brens (MK1 & MK2 U.K. de-acc) and have had the Butt slides in pieces. While doing this I noticed that behind the "Rat's Tail" on the MK1 Bren was a double (inner & outer spring) which fits inside the Butt.


Being an engineer by trade I made a point of examining them in detail and found that the springs were wound in opposite directions to each other as I would have expected to avoid them fouling/clashing on each other. The other application where I have encountered a double spring arrangement is on motor car valve springs when double springs are fitted. I was alerted years ago to always ensure double car valve springs are wound in opposite directions to each other to avoid them fouling by a specialist firm who made a set for me.


Has any-one encountered problems with the double Rat's Tail springs sometimes fitted to the Bren? Is any-one aware of any official instructions to insure that the springs are wound opposite to each other?


I will be interested to hear the thoughts of others on this subject and thanks for any info.

Interesting........ and this very subject has been aired here before. Mechanically, multiple spring should be would and used opposing. This prevents the inner spring coil binding the outer (which is supported externally by the return spring tube of course). It's the ROD, return spring by the way!

I have just looked at 4 sets of springs. In a Bren, the outers (C1-BE6897) are all the same (except for a very minor change on the very earliest Mk1 guns) as are the inners (C1/BE6896). All of the outers are wound the same way and 3 of the inners are wound in the opposite direction. The 4th inner being would the same way as the outer. And operates perfectly!

What is very interesting is that nowhere in the technical information, the EMER's, parts lists, technical spec, Inspection standards etc etc does it specify that the inner spring should rotate opposite to the conventional outer spring. Indeed, several years ago I published an Armourers crib-sheet for the identification of the many Bren springs...., some VERY similar but soooooo different in application. I think that in this case, it doesn't matter as coil binding will not(?) be a problem. In the Sterling SMG the tech spec distinctly states that Armourers will find return springs wound in either direction.

And what about the L1A1 rifle double return springs.............. I think that this will run and run awhile

I think the diameters of the springs and the distance between coils is what keeps them from binding. Same with the FN49’s triple return spring setup.

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Originally Posted by Peter Laidler

In the Sterling SMG the tech spec distinctly states that Armourers will find return springs wound in either direction.

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That’s interesting, Peter. It never crossed my mind to look for that.

Guys,

Attached are the return spring specs from the "Bren Manual".

Joe

Yep, you've got it in one Joe. You can rely on Joe to turn up trumps! According to the current up to date EMER that we worked to and that I have in my grubby little mitts, E-554 (Field and Base standards) Misc Inst No2 (yours, as above) was incorporated into the Inspection Standards in August 1961. But it doesn't now detail direction of twist.

This could also answer something else too. (Joe you've opened up a bag of worms too......) IF, like me, you have an inner and outer return spring coiled in the same direction, it will mean that you have a LEFT 62-coil MK1 outer spring with a LEFT coil inner spring.

That's clearly the answer to the mystery. So if anyone has an early Mk1 gun, then it will have a 62 coil single return spring. I can already see those early Bren affectionados carefully cutting the first 6 coils from their current 68 coil Mk2 return springs................

Any UK forumers need a virtually new condition Mk2 before the deact rules change please ask now or forever hold your peace!

I was curious if I had any Sterling springs wound in either direction. Could I really miss something like that?

https://www.milsurps.com/images/impo...0springs-1.jpg

Now I am curious why I never noticed that before. :lol: :D

Same reason why I never noticed the same with the Bren Vince....... The difference is that it was pointed out in the Sterling technical info but not in the Bren. Well, it WAS until it was deleted in 1961!

Maybe you could put this plus your photos in the SMG thread too

I am bound to ask the obvious question that if it was felt necessary to increase the tension/pressure of the springs why not simply use a heavier load spring? This is normally what I would do in tool-making if I thought greater spring pressure was required. I have never liked the idea of an inner and outer spring arrangement.

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Originally Posted by Flying10uk

I have never liked the idea of an inner and outer spring arrangement.

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Works exceptionally well in performance automotive cylinder head springs. Generally the issue with using a heavier load spring is the thicker wire used to make the coils, which then lowers your spring bind height and overall travel. Coil bind in an engine application is generally catastrophic when it does happen. It's almost worse than not having enough spring pressure really, a Ford 5.0L Windsor V8 had a fuel cutoff limiter programmed at 6,250 RPM, but in a stock configuration you would seldom touch it, the light pressure springs would generally float the valves around 6,000 RPM, like a soft limiter. Installing springs that were too short in their bind height would generally break parts when everything stacked up solid at speed.

For firearms I am sure it is a matter of packaging or other similar consideration.

There is a loooooong sorry story regarding why the Bren was changed to double recoil springs. And this change was the last ditch effort to improve its reliability and breakage rate.

One day I'll relate it all. But get your tissues out because now, while the Bren is regarded as the best, most reliable machine gun ever to grace the battle field, it didn't start like that when it first went into action. It was a total pig in a poke

The thing that I don't like about having 2 springs working closely together is that if one spring fails/breaks then the broken parts are liable to foul on the other spring. With press tools where compression springs are commonly used as part of the tool to strip metal off punches and to keep metal flat I don't recall ever fitting an inner spring to increase spring pressure. I did sometimes fit an extra spring on another part of the tool and also increase the size of the spring.

I can understand that, however the main take away in a firearms application, breaking one spring of any sort generally puts a gun out of operation, if it knocks another out along the way the net change is still a spring assembly replacement.

With the field tool roll for the C6 (FN MAG 58, L7, M240B pick your name) we would carry a spare recoil spring and guide rod assembly for repairs. The change would take less than 30 seconds, and breakages were rare. I can't recall if they were a single or double spring, but my point is, for field repair we would just change assemblies. With the "school guns" provided at training centers for Machine Gun courses we would generally see failures relating to wear and tear of extremely high round counts with guns approaching the end of their service life. With one of these such guns I had the cocking handle tear off in my hand while clearing a stoppage on my gun in the Sustained Fire Role. From there it was a matter of opening the feed cover and hooking a length of cord on the feed roller like a garrote and clearing the gun.

Our first line and deployment guns were in much better condition, and seldom had any major issues. Having a junky MG for training is better anyway, gives a gun team lots of practice on IA's and stoppage drills. LOL.

My guess is a sufficiently stronger spring would not work in the tube assembly. That’s because it would be made from thicker wire. Thicker wire would increase the solid length and change the working length of the spring.

Adding the inner spring maintains the same solid length and working length of the spring. So there’s no need to redesign the whole assembly.

The application of the double return springs in the Bren was for a slightly different reason. For the Bren it was to cushion the violently recoiling portions so that by the time the heavy piston, piston extension, piston post etc AND breech block reached the buffer most of the kinetic energy had been removed and the working parts hit the buffer at a reduced rate. Previously to this they were slamming into the buffer and causing a radial fracture to the buffer plate. There WAS a slight increase in the double return spring weight over the single return spring weight but if my memory serves me right, it increased from 13.5 lbs to 16 lbs from the cocked position. Feel free to correct me if the figures are slightly incorrect. But it was a small price to pay and although piston/body buffers did fracture it was a rare occurrence. And while we always polished the face of the buffer they were well hammered and by polishing them we could see the start of any trouble

Previous to this double return springs episode, it was the piston post, spring and plunger that got a hammering as the piston, piston extension piston post etc struck and unlocked the breech block due to the much increased gas caused by the enlarging of the gas ports, The plunger bottomed out in the piston post causing it to mushroom out deep in the hole, jambing the spring onto the post (rendering it totally redundant thereafter) so that any buffering of the piston post as it unlocked the breech block was non existant.

Is anyone interested in this guff.........? Anyway it was PARTIALLY cured by the new Mk2 piston post and plunger that couldn't bottom out and jamb up together but in doing so, broke the piston post springs at approx 70,000 rounds. That's the reason why your Bren gun spare parts wallet contains a spare piston post spring. There, a small bit of Bren Gun History

So mote it be!

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Originally Posted by Peter Laidler

Is anyone interested in this guff.........?

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Yes. I am very interested and appreciate you taking time to share it. :)

I am also looking forward to the book.