Spec for mag spring....official? (Judging worn flat springs)

[TactAdv]

Okay.....I'm not completely FNG here.....but I couldn't specifically locate any discussion of this on the forums so I'm putting it up as a new topic.

I've noticed, much like USGI BAR mags, a considerable difference in both tension and free height among many of the BREn magazine flat springs I've disassembled from various mags I have.....both from mags seemingly in still excellent condition and from those that are clearly "well experienced/well travelled".

I am interested in any "official" specifications extent or known that clearly deliniate "new"/"ideal"/or otherwise "original" parameters for free height, tension/compressive force when new, and then obviously the other end of the spectrum as to when indications present notice to trash them/replace?? (And I will assume since I do not actually know that there was only ever ONE BREn magazine spring produced?? And that all spring "coil"(flats/bends) were of a singular specification?)

I shoot my still-all-original Daimler MK II a LOT and in fullauto mode it delivers a noticeable disparity in cyclic rate of fire with different mags used, an audible difference. I am about at the point of just replacing like a group of 20 mag springs with NOS Canadian spares.
-TomH

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[Peter Laidler]

There were several variations of mag springs Tac. Hold on for a day or so and I'll dig the specs out.

But your para 4 is a bit of a mystery because the only way a magazine will affect the functioning of a gun is the friction of the top round* in the mag which frictions on the top surface of the breech block. And even then, it is only one VERY narrow area that frictions and even then, only in two very small places.
* out of interest, there is an argument among nerds that the round closest to the feed lips is actually the BOTTOM round in the mag. And the TOP round is against the follower, deep inside. As a result of this, which apprentice Armourers would discus at some length with the obnoxious Mr Weekes, the '6-div' Bren teacher the pro's and con's of it all. As a FURTHER result of this, so as to clear out any ambiguity during exam times, we had to start any related answer with EXACTLY what we meant by TOP round and BOTTOM round.

[CINDERS]

With the miniscule practice we had with the Bren we only loaded 28 rounds as per instructions from the W/O in charge from the Army, I suppose Peter you could have argued with the Mr Weekes that the top and bottom round could be named indicative to the Mag floor plates relation ship to the vertical if it was held inverted then the bottom round on the floor plate of the mag really is the bottom one and not the top one. But right way up it assumes its role of the top round. Mind you I can imagine you burning the midnight oil with the other apprentices on who would draw the short straw to argue the point with the obnoxious Mr Weekes, hope you did not get that short straw, if you did I hope you went down fighting in the best British tradition............

[Kev G]

Here's something to be going on with .

Attachment 82266Attachment 82267

ATB Kevin

[Peter Laidler]

Can't get better than that. I seem to recall that the Mk1 spring had tight bends that were prone to stress fracture at that point.

The note at the top of photo 2(above) regarding the cramp test made me chuckle. As Armourers we were also semi-trained in the mystical art and sciences of......... blacksmithing!!!!!!!!! And as well as a bit of spring making we had to make a..... spring. Said spring could range from a .55" Medium gun recoil balance spring to a small revolver V spring, depending on the whim of the teachers whose names I still remember. Mr Milo and Mr Owens. Our finished work would be cramped up in a vice for a compression spring or extended between two points for a tension spring. If I was brutally honest, you could just tell when your tension spring was stretched that at a certain point it was going to just give up with a metallic groan. OR, ...... it was going to shatter into many bits. This was to test our understanding of tempering, temperatures, hardness, cake making and sock darning so far as my interest went. Everyone seemed to fail but by the end of the month long magical mystery tour everyone seemed to have the hang of it - which was soon forgotten by the end of the following month

[TactAdv]

Thanks guys! Excellent answers as always.....

Peter- yes, it's due to increased stripping pressures as exist in "new" mags versus lessened pressures with more experienced ones. And it isn't much, the drop in cyclic ROF, but it is definitely audible...... much like you can easily detect the cyclic ROF differences when using different ammo choices. It's there, and I'm going to guess something along the line of 25-30 RPM.....

Kev- greatly appreciate the drwg! Just what I need. I'm going to pull a bunch of my mags apart and get some empirical measurements therein, albeit from an admittedly small population sample...
-TomH