The recoil and reciprocating buffering action

[Peter Laidler]

Is anyone interested in reading a semi-technical article on the two part gun and working parts action of the Bren buffer? Taken from Advanced MG tech/design course notes?

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[scoobsean]

Is anyone interested in reading a semi-technical article on the two part gun and working parts action of the Bren buffer? Taken from Advanced MG tech/design course notes?

Absolutely. I throughly enjoy your technical articles

[TactAdv]

Absolutely!!
-TomH

[browningautorifle]

I always like a good tech article...

[Peter Laidler]

Ok, point taken. Will get it out andget started on it.

KevG..... Have you got a good side elevation pic of a skeletonised buffer?

[tankhunter]

Peter, I always enjoy your Technical Articles. They are delicious! Mmmmmmmm..................................

[Peter Laidler]

Excuse me if I’ve been here before but thought I’d change the thread where scooby-doo and I had been mentioning the importance of buffering your Bren. I hope that this little technical article illustrates just how important it really is. Not so much on a deactivated but if it's there, then let's have it working correctly!

Get your Skennerton ID ready-reckoner SAIS book handy and open at page 32/4/6 and here we go.... But before we do, here’s a bit of Bren Gun history. Originally, the actual GUN buffering was going to be achieved by the buffer at the end of the Mk1 butt while the PISTON buffering would be achieved by the buffer built into the buffer housing at the rear end of the butt slide. But early on in its trials and UK development at Enfield, the Enfield designers suggested that with a bit of thought and a simple re-design/reshape (more later), the piston buffer could do BOTH. It could be both a gun AND piston buffer, virtually making the butt buffering system redundant. In fact, and without putting it too mildly, a Mk1 Bren user can forget the BUTT buffering mechanism as shown for the Mk1 gun on p.32. If you want the real truth, after the Enfield development input, this became a frill if not a complete fraud – and a VERY expensive one at that. But it came with the licensing agreement as a package so it stayed – until times and finances dictated otherwise!

The GUN buffer we are interested in is shown in parts form on pages 32,34 and 36 of the SAIS booklet and elaborated on with some of my rubbish photos too!. The parts we’re going to look at are the parts sandwiched between the TUBE, return spring and the SLIDE, butt. Let’s look at them. They are the:

BUFFER, Piston, The NUT, piston buffer, the COLLAR, friction, the SPRING, piston buffer and last but not least, the TUBE, return spring again and they’re all housed within the buffer housing at the rear end of the SLIDE, butt.

The component parts LESS the butt slide shown in actual form. A compressed copper ‘spring’ is shown in place of the fully extended true spring.

Attachment 64710


Same as in photo above close up, but notice the split brake ring or phosphor bronze collar

Attachment 64712

The most important part of this whole operation is the BUFFER, piston. This name of PISTON buffer is a throwback to the earliest days we mentioned earlier when this item was in fact the buffer for the piston extension and breech block assembly (the PE&BB assy) alone! This grey or silver faced flat buffer is the part that’s visible at the inner end of the butt slide. Notice that its outer edges are shaped to and fit snugly inside the rear of the gun body. This was the Enfield input whereby the gun body rests on and around the edge the buffer and it is THIS buffering that makes the gun such an easy and relaxing gun to fire.

So exactly WHAT happens when we fire the gun? Immediately the gun has fired and before any of the other associated/resultant actions* takes place, the heavy 18lb gun body, barrel and BB&PE assy. recoils for about ½”along the butt slide and AGAINST the outer edges of this buffer plate. The buffer assembly does exactly that – it buffers against the buffer plate and spring and then immediately, the buffer spring reasserts itself. But there’s more to it than that....... There’s the mechanics of it. The buffer plate is held into the buffer housing through the rear by the buffer nut which together can move fore/aft by ½” or so. This is the distance through which the body locking pin can travel as the gun recoils. The rear end of the buffer nut is angled inwards radially towards the rear. Sat onto this angled rear portion of the nut with an identical angled mating inner surface is the split phosphor bronze friction collar or brake ring. This bronze friction collar has been called a ‘clutch’ but it’s nothing of the sort. And some repro collars have been manufactured recently from brass and without the split, making them effectively useless! Sat on top of the split friction collar is the heavy duty piston buffer spring. We now compress the buffer spring by inserting the return spring tube into the buffer housing within the butt slide and screwing it down against the threaded flange. You can see now that the heavy duty spring has been forced down and compressed onto the split collar. The angular surfaces of the collar and the nut have caused the split collar to spread and radially grip the side walls of the buffer housing. Clever eh!

(* such as unlock, extract, eject, etc etc)

Close up of the split in the collar. This allows the collar to open up radially into and grip the walls of the buffer housing.

Attachment 64713


The nut and collar. Notice the matching tapers that act together causing the collar to act as an effective brake. Clever eh!

Attachment 64711


Now, when the buffer is forced back by the recoiling gun body, the buffer nut taper acts against the corresponding split friction collar taper which moves rearwards too. This all acts against the heavy duty buffer spring which stops against the threaded part of the return spring tube! And that ain’t movin’ nowhere fast! Simultaneously during this rearward movement of the buffer, nut, collar and the compressing of the spring, the friction collar spreads itself further and firmly radially grips the radial internal walls of the buffer housing. The friction caused by the split collar is a VERY effective form of braking AND obturation similar to a tapered spent case tightly gripping the walls of the chamber.


Are you with me so far? This is the action of the buffer during simple gun recoil. After recoil has ceased, the buffer spring simply reasserts itself and now under reduced friction, the split collar forces the nut, plate and gun forwards into battery and prevented from further movement by the body locking pin. But there’s more. The piston buffer assembly also acts in a secondary action too. And on the advanced automatic/machine gun courses these actions were always highlighted and clearly/easily visible on the high speed video to illustrate their importance. It was also argued that this secondary action is more important than the initial recoil buffering.

As soon as the gun has recoiled the spring loaded buffer recuperates and returns the buffer and the gun to battery. A millisecond or so later the gun starts to unlock and immediately the gun has unlocked the heavy reciprocating forces start to act. These are the heavy dead weights of the BB&PE assy being virtually and literally blasted rearwards and this dead weight is aggravated by being increased/accelerated by the inertia of the operating gas.

And it is this additional force that our buffer plate has to effectively control. Yet again, the same buffering cycle takes place, this time it’s not the recoiling gun that it has to look after....., it’s worse than that. It’s the reciprocating weight of the BB&PE assy. Without this effectively buffered plate, this hammer blow will soon make life very uncomfortable and will damage the buffer plate and internal parts of the system. During the recoil buffering the external edges took the load, now it is the centre of the buffer plate that takes an even greater load crashing into it at 10x a second! Now you can see why they always look so battered and bruised. It is for this reason that Armourers keep them polished, so they can immediately see anything untoward that might be happening - like minute cracks – and even large cracks!

A good example of a well battered piston buffer plate. Notice the clear outline of the gun body around the edges. A quick polish and this’ll be perfect again

Attachment 64714


There you go. Polished and as good as new.....

Attachment 64715

So what will happen if you’re missing the parts of the recoil buffer? In short and without mixing words here, the recoiling gun and reciprocating PE&BBAssy will simply batter the front end of the return spring tube to pieces and in short order thereafter it’ll destroy the buffer housing.......... Look...., don’t even think about it!

How can I check whether my buffer is working properly? It’s quite simple. Stand the assembled gun on the muzzle and press down on the butt (remove the butt plate if you have a Mk1 gun). You should feel the gun buffer squeezing up and recuperating on the heavily graphite greased buffer. Feel the movement carefully through your sensitive finger tips........ It should be smooth and free running, no hesitation, no fouling and definitely no graunchiness. That’s all there is to it

[TactAdv]

Excellent discussion , Peter! Thanks.

I might add the proper terminology/name for the split-ring "buffer" is a Belleville Washer assembly, pretty commonly used in many mechanical devices up till the advent of elastomeric bearings.

Besides the BREN gun, it's well found in the Browning BAR series of LMG's, albeit in a "stacked" arrangement of multiple sets as opposed to the single set in the BREN.
-TomH

[TactAdv]

Hmmm, I will have to amend my last post on this- apparently, it seems the once-common terminology I used, just saying a "Belleville washer" assembly now is taken to mean JUST the singular beveled spring portion, now almost exclusively a flat-punched sheet steel washer at that, and "cup-and-cone" assembly is now the common terminology preferred for the multi-part assembly using bi-metallic parts, and more to the point, having the beveled part with a cut ring instead of a bevel face exclusively. I also just saw these are apparently also called a "Jones" buffer in certain applications.

From my background, we always knew them as "Belleville assemblies". Live and learn....more.

-TomH

[Peter Laidler]

I did question your thread 8 at the time and to me, the beleville principle is the pressing together of the concave sections of round washers, a bit like pressing your finger tips together for want of an everyday example. The Bren spring loaded split brake ring/collar is a slightly different principle I feel. I seem to recall that our M1919 brownings had fibre washers like the Thompson while our 50's and GPMG's had belevilles. Thread 9 clarifies it. Good discussion........