Double "Rat's Tail Springs"

[Flying10uk]

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.

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Peter Laidler]

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

[Vincent]

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.

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

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

[Joe H]

Guys,

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

Joe

[Peter Laidler]

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!

[Vincent]

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



Now I am curious why I never noticed that before.

[Peter Laidler]

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

[Flying10uk]

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.

[Sentryduty]

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

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.

[Peter Laidler]

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