Operating principles of WW2-era wpns

Site Issues 2005 Archive Room
#1

Since Ironman wants to start anew, here’s a new thread where he can share his infinite wisdom with us.

Right.

First off, to clear up one of Ironman’s misconceptions, although it is true that automatic wpns are actuated using energy from the cartridge, it is excess energy (of which there is loads) that is used, and not energy which would otherwise go into propelling the bullet - the amount of gas taken off is tiny (or occurs at the muzzle after the bullet has left it), and recoil operation has no meaningful effect. Maxim invented the concept of recoil-operation after getting pounded by a rifle & decided that this excess energy could be harnessed, and Browning saw long grass being blown about by powder gases and invented the principle of gas operation to harness this excess energy. This does not result in a meaningful reduction in muzzle velocity, and certainly not enough to meaningfully consider a self-loader as less powerful than a bolt-action!

Here we go:

SMGs in general work like this:

The receiver of an SMG is basically a metal tube. It might not be round like the STEN, but it’s a tube nonetheless. Attached to this tube are a magazine housing, a butt, a barrel, and a trigger mechanism.

Inside the tube is a spring and the breech block (sometimes called the bolt). The spring is generally behind the breechblock and serves to push it forward. The breechblock holds the extractor and (normally) a fixed firing pin. In the STEN, this is machined into the face of the breech block.

When firing an SMG, the breech block is pulled to the rear, where it is held by the sear (part of the trigger mechanism). A magazine, if it has not already been inserted, can be inserted now.

On pulling the trigger, the breech block is released. It runs forward freely for a distance, before contacting the top round in the magazine. It pushes this into the chamber, and just before it would come to rest, the fixed firing pin ignites the primer of the chambered cartridge. This is called “advanced primer ignition” and allows you to reduce the weight of the breech block and/or the strength of the spring. The bullet is now accelerating up the barrel, and the pressure is pushing the cartridge case back against the breech block, which does not lock. This pressure forces the breech block to stop moving forwards, and then to accelerate backwards. By the time it is moving backwards with enough velocity, the bullet is long gone.

The momentum gained by the breech block carries it to the rear, where it ejects the spent case. As it reaches the sear, if the trigger is still pulled the process repeats, otherwise the breech block is held by the sear.

No hammer, no lock, almost nothing.

The Garand works like this:
The bolt is rotating, and is actuated by a cam on the operating rod. This operating rod carries the charging handle, and terminates in a piston in the gas cylinder.

The bolt is pulled to the rear, and an en-bloc clip of 8 rounds is pushed into the magazine. The bolt is then tapped forwards, and chambers the first round (if it didn’t run forward & take your thumb off when you pushed the clip in).

On pulling the trigger, the hammer falls, striking the firing pin which actuates the primer of the cartridge. The bullet now accelerates down the barrel. The last inch or so of barrel is freebore (i.e. is slightly oversize and has no rifling - see patent US 2 287 032) About an inch from the muzzle is a transverse gas hole at the start of the freebore portion. Once the bullet has left the rifled part of the barrel, gas moves through the transverse hole and into the gas cylinder, where it acts on the operating rod. The operating rod then pushes the bolt back, and it is returned to battery by the mainspring.

The gas used is excess, and the bullet would not accelerate any further in the freebore portion of the muzzle had there been no gas takeoff!

The M1 carbine works like this:

The bolt is pretty much a scaled down Garand bolt. The difference is in the operating mechanism. Because the .30 carbine cartridge is significantly lower pressure than the .30-06, the gas takeoff needs to be closer to the breech. Williams had the insight to realise that a long-stroke at lower pressure was not necessary for the piston, but that you could use a very short stroke at higher pressure coupled with a heavy operating rod.

Thus, you insert the magazine, pull back the charging handle, release, and pull the trigger. Hammer falls, etc etc etc, bullet passes the transverse gas hole, and some gas is taken off & enters the gas cylinder. The gas cylinder moves back very fast about 1/10", where it is stopped by a ring. As it moves back, it pushes the operating rod, giving it momentum. This then causes the bolt to move backwards, and once it has reached its rearmost point, it is returned to battery by the mainspring which is situated under the barrel, acting on the operating rod. As the operating rod comes to its foremost position, it pushes the piston back into place, venting any remaining gas back into the barrel.

Again, the amount of gas taken off is very small compared to the amount present, and thus results in no meaningful loss of muzzle velocity.


Colt M1911 pistol

The barrel and slide are locked together. On firing, the bullet accelerates down the barrel, where it exits the muzzle. The recoil of the barrel and slide causes them to move back together. They remain locked for a short distance (to allow the pressure to drop), and then a swinging link lowers the back end of the barrel and then arrests its movement, unlocking the two and transferring the momentum to the slide. Slide moves back, ejects case, mainspring brings it forward & chambers the next one. When the slide hits the barrel the swinging link causes it to rise & re-lock. No reducion in muzzle velocity from the self-loading mechanism.

Recoil operated rifles (e.g. Johnson) and MGs (e.g. Maxim, Vickers, MG34, MG42 [although the latter 3 are gas-assisted by muzzle attachments]) work on similar lines - the barrel and breechblock recoil together a short distance (normally, except in some pants designes like the Chauchat where they move to the rear together), whereupon the barrel is stopped, the breechblock is unlocked, and the breechblock carries on to the rear under the momentum it has gained. No meaningful reduction in muzzle velocity is caused by this (if you want to be really anally retentive, the muzzle velocity is reduced by the speed of the barrel moving rearwards, although this speed is so small when compared to the velocity of the bullet as to have no meaningful effect).

Revolvers

Cylinder butts against the barrel, but there is necessarily some gap. Cartridge is fired, bullet leaves cylinder & enters the barrel via the forcing cone. Gas is lost through the flash gap, where it does no useful work. Shotgun News did some experiments concerning flash gaps using the M1895 Nagant revolver, which uses an elongated cartridge case to seal the flash gap off. By comparing the velocities of normal cartridges with those that had been cut back so that they would not seal, they found that the flash gap accounted for 100 or so feet/second of muzzle velocity (IIRC, it’s a long time since I read the article - it wasn’t as much as had been expected).

So there you go.

#2

Thank you I enjoyed that. Most of what you said I was aware of. But clearing up some of the action and confirming what I thought.

Having use the GPMG and knowing how It’s feed mechanism works, which I think Is based on the MG42, I was surprised when stripping a Vickers to find it so different. I also feel that early weapons (WW1) seem to be over engineered. What I remember of the Thomson was that it was very heavy and made from milled blocks, the same would be for the Vickers. Is this an assumption of early technology?

#3

The MG 42 is a recoil operated weapon. You pull the charging handle back, this moves the bolt and the locking piece back, until it catches in the sear.
Then you put in a belt with the links lying on top from the left side. The linnks, which are split on the now lower side, act similar to the feed lips of a box magazine. When you press the trigger, the bolt and locking piece will move forward, stripping the next cartridge from the belt and push it into the chamber. Once the cartridge is seated and the bolt face contacts the barrel, the locking piece keeps being pushed forward by the main spring, and since it is wedge shaped, it will push two rollers out sideways, which will lock the bolt in the barrel extension. Then the firing pin, which is also driven forward by the main spring will contact the primer of the cartridge, firing it.
The bullet will be driven down the barrel and the barrel, which is attached in a loose fit, will move backwards due to the recoil. The recoil is supplemented by gas pressure of the excess gases, which expand in the recoil increaser in the fire damper assembly.
The movement of the barrel and the barrel extension will force the locking piece back and the rollers back into their slotas in the bolt. At the same time the bolt will be given a kick by the barrel extension, causing it to move backwards against the mainspring. Moving backwards, it will strip the empty case from the breech and dump it downwards, move the feed arm, which is connected to the bolt assembly by a roller to move the belt one cartridge to the right (same as GPMG) and if the trigger is not being released the whole procedure will happen again.

The Vickers, while also being recoil operated, it also uses a sliding barrel to transmit the forces, uses a toggle joint (similar to one´s knee. bit like the Luger pistol) for locking. On moving back a claw on the brech block will pull one round from the webbing belt, which on the next movement forward of the breech block, will move downward into the chamber and get fired. On the next move backward, the empty shell will be extracted from the breech and dumped out of the gun, while at the same time the next cartridge is being pulled out of the belt.

The GPMG, while using a feed mechanism based on the MG42 (as does the American M60), is gas operated and uses a locking mechanism very similar to the Browning BAR, just upside down.

Jan

#4

The fundamental difference between the Vickers (& Maxim & Browning M1917/M1919) and the MG34/42 is that in the former, the cartridges must be taken out of the belt backwards, then lowered & chambered. This is known as “pull feed”, and is due to the canvas belts used. In the latter, they are stripped out forwards straight into the chamber, which is known as “push feed”.

There’s also a difference between the MG34 and MG42 feeds - the MG34 only has 1 claw, and pulls the belt in jerkily one space at a time. The MG42 has 2 claws, and pulls it 1/2 a space at a time. If you ever get a chance, lift the top cover on a 42 and push the camtrack left & right - it’s absolute poetry in motion.

(edited to remove typo - thx 2nd of foot)

#5

Man of Stoat,

Thanks for the info! I didn´t have the opportunity to take a MG 34 apart so far, though I´ve stripped Bren guns, MG42, Stens and played around with a Vickers (Partially stripping it). AFAIK the biggest difference to the MG42 is that it used a turning bolt to lock, not the rollers like the MG42. I also find it quite difficult to explain complex mechanics without the aid of drawings.

Jan

#6

Man of Stoat

do you want to edit that last as i think you have sliped and i would hate to have it used against you.

i found teh method of the empties slowly moving down in the vicker just so simple :smiley:

#7

Other operating principles:

The Bang principle.

John Browning’s first patent for a self-loading rifle concerns a modified Winchester lever-action. As already stated above, he noticed that the muzzle blast from a firearm made long grass move significantly. He thus modified a Winchester by placing a small cupped plate with a hole in the middle on a lever over the muzzle, with an operating rod extending to the trigger guard (which forms part of the lever). Several springs were provided to return the lever to battery. On firing, the bullet passes through the hole in the plate, and the gas leaving the muzzle pushes it forwards. Since it is on a lever, it hinges forwards and down, and thus pulls the operating lever forwards.

This in itself was not a practical weapon, but more a development concept that allowed Browning to claim a patent for the gas operation of a firearm (I’ve seen this patent, and if anyone’s interested, PM me & I’ll find the number when I’m in work on Monday)

Browning then developped this further for a machine gun made using the same principle (which was prototyped), and then further for a machine gun working by blowing vanes around with the muzzle blast (patented but never adopted), and then hit on the idea of the transverse gas hole in the barrel and took the muzzle blast idea no further.

A Dane by the name of Bang (ironically) did take the idea further. He used a movable sleeve over the muzzle, with the end posessing a hole just large enough for the bullet to pass through. When the rifle was ready to fire, there was an airgap between the end of the barrel and the end of the sleeve (formed by making the end of the sleeve conical), to act as a gas trap. On firing, the sleeve is blown forwards by the muzzle pressure trapped between the barrel and the sleeve. The sleeve is connected to an operating rod, which terminates in a lever, one end of the lever being connected to the op-rod, the other end resting on the bolt carrier. Thus, when the sleeve is blown forwards, the end of the lever pushes the bolt carrier backwards over a short distance with great velocity (i.e. short-stroke).

The German military initially had a design constraint on self-loading and automatic weapons, that the barrel was not to be tampered with. They believed, falsely, that this would weaken it. This is one of the reasons why the MG34 and MG42 use a gas-assisted recoil operation, using a muzzle attachment to force muzzle gases to act on the front of the barrel to help push it backwards to increase its recoil.

Thus, when a request for designs of a self-loading rifle was produced, designers were left with the prospect of recoil operation (which results in much higher felt recoil, is complicated, and requires many precision-machined surfaces), or the Bang principle. There was also, btw, an auxiliary request that the rifles must have no externally moving surfaces and that they must be suitable for use as normal bolt-action repeaters should the self-loading mechanism fail.

This resulted in two rifles, both working on the Bang principle: the G41(M) and the G41(W). M stands for Mauser, and W for Walther:

Battle pics of G41(M) and G41(W)
http://www.gewehr43.com/battle.html

The G41(W) - note the bulbous Bang muzzle attachment

The G41(M) fulfilled the specification perfectly - it even posessed a bolt handle that could be worked rather like the Mauser bolt-actions. However, it was unreliable in combat. The G41(W) did not completely fill the specification, since the bolt carrier moves externally, and it can only marginally be used as a straight-pull bolt action should the self-loading mechanism fail, but was significantly more reliable and simpler to produce.

There is a reason that the Bang attachment has never had any real success - it fouls quickly then jams, and it is very sensitive to dirt.

By this time, the Germans were capturing significant numbers of Tokarev SVT38s and SVT40s, which were often used by German troops as substitutes for their own weapons, and they were well-liked. The Russian conscript infantary didn’t like them, since they required lots of cleaning and were more complicated to use than a bolt-action.

The Germans then looked at the success of the SVTs and realised that it did not weaken the barrel by boring the transverse hole to tap gas, and the G41(W) was quickly re-designed to use the Tokarev gas system, the bolt and carrier remaining essentially the same. This became the G43. The G41(M) was a dead-end and was not developped further. In the meantime the FG42 and MKb42 had been designed, which also used a transverse gas hole. The prejudice against it was thus laid to rest forever.

G43 rifle - note that the receiver is identical to the G41(W), and the magazine is not attached

The Tokarev/G43 gas system involves taking gas from a port in the barrel under a gas block quite a distance back from the muzzle, and directing it into a gas tube, which projects from the gas block towards the action. Over the gas tube is a gas cylinder which is a sliding fit and posesses vent holes to limit its motion under gas pressure. This sliding gas cylinder is attached to the operating rod, which contacts the bolt carrier.

On firing, the bullet accelerates along the barrel and passes the gas port. A small amount of gas is directed into the gas plug, via the gas block. This acts on the gas cylinder, pushing it to the rear until the vent holes are exposed by the gas plug, and then the excess gas is vented. The bolt and carrier continue to the rear, whilst the op-rod spring returns the op-rod and gas cylinder to their rest position. The mainspring returns the bolt to battery, where it is locked by means of a pair of flaps (the Tokarev is locked by a tipping block).

(NB - no cut & paste: do I get a gold star, miss? 8) )

#8

Luger P08

One of the earliest practical automatic pistols, initially adopted by the Swiss as the model 1900 in 7.65Para (looks like a necked-down 9mm Para, whereas in fact the 9mm Para is an un-necked 7.65Para).

It is derived from the Borchard pistol, which was an ungainly beast.

It uses a toggle-lock similar in concept to that used in the Maxim & Vickers machine guns, and also in the Furrer M25 LMG (a Swiss design). It works like a knee joint: when the pistol is ready to fire, the “leg” comprised of the two joints of the toggle is straight, or in fact slightly downwards-cocked. It thus holds the breech firmly shut. The barrel & toggle are free to slide backwards & forwards on the frame to a small degree. The “knee” of the toggle has two round protrusions which serve as grips to cock the pistol, and also contact a cam track on the frame.

On firing, the barrel and toggle recoil together a short distance, and the two protruberances run up the cam track on the frame. This breaks the toggle joint. The toggle then opens upwards under its momentum and any residual breech pressure, ejecting the empty case. The mainspring then returns the toggle to the straight position, and returns the barrel to its foremost position, ready to fire again.

The disadvantages of this system are that there are many finely machined surfaces, and some degree of hand-fitting is required. The whole mechanism is also exposed, and is therefore dirt-sensitive. Advantages include an extremely fast cycle time (almost impossible to see), and a compact mechanism with very little metal moving when firing.

Because of these disadvantages, the Luger was superceded by the Walther P38.

NB - not a german luger, but an informative picture

Walther P38

The P38 is a recoil-operated pistol, but functions in a different way to the Colt 1911. Whereas the Colt 1911 uses a dropping barrel to lock & unlock the barrel and slide, the P38 uses a wedge, and the barrel moves linearly.

When the barrel and slide are in battery, the wedge is raised and locks the two together. On firing, the barrel and slide recoil together a short distance (calculted to ensure that the chamber pressure has dropped to a safe level) , and at the end of this travel the wedge is cammed downwards. The barrel is arrested, and the slide continues to the rear under its own momentum against the mainspring, cocking the hammer and ejecting the empty case. The mainspring then returns the slide to battery, having caused it to pick up a fresh cartridge from the magazine.
As the slide meets the barrel, the wedge is cammed back up, locking the barrel & slide together. When the barrel and slide are fully forwards, the pistol is ready to fire again.

This system is not as good as the Browning dropping barrel, since there are more sliding surfaces to be precisely machined. It is therefore more dirt-sensitive.

Walther continued the system with the P5, and then dropped it with the P88 and P99 in favour of the Browning system. About the only other example of this system still in use (off the top of my head) is the Beretta 92 (& derivatives), all other manufacturers now using the Browning system.

#9

M1 Garand and M1 carbine exploded drawings, for info:

http://www.schiessen-erzgebirge.de/Blueprints/US_Carbine_cal_30_M1.jpg
http://www.schiessen-erzgebirge.de/Blueprints/m-1_garand.gif

#10

K you have 3 posts in a row. But go ahead and try now.

#11

I have just acquired a nice copy of Small Arms Of The World, and I should point out that the Bang system used in the G41 rifles is not quite the same as the Bang system described above (which is after Hatcher, op cit, p.61) - it uses a floating annular piston around the barrel which is acted on by gas directed by the blast cone rather than the usual blow-forward Bang system. Sorry! (SAOTW p. 416)

#12

Any news on Roller Delayed blowback?

I know its a trademark of Hk, but was wondering whether it has any predecessors or if its only been used by HK. Bascially Im interested, please continue.

Bluff

#13

The Stg 45 - it’s roller lock provided the basis for the CETME which later became the G3A2.

As an aside there was an interesting magazine produced for the CETME which had a rubber ‘boot’ instead of a floorplate.
The boot could be removed revealing another set of mag lips and lug to fit the FAL, ideal for those armies using a common cal for two weapons. Shame it didn’t pass muster.
There ain’t half been some clever b*stards !

#14

AFAIK the Stg 45 has been designed by Mauser. After the war the German technicians from Mauser found themselves without a job and got hired by the Spanish Centro de Estudios Technicos de Materiales Especiales (CETME). There they continued their work and developed the CETME assault rifle for the Spanish military.
When the Bundeswehr was established in 1955, after a period where they used the surplus of WW2 (Garands, M1 Carbines, Lee-Enfields etc) the German government became interested in the FN FAL of which they bought a few thousand and introduced them as the G1. Unfortunately the Belgians didn’t agree to licencing the production to a German company, which the German government wanted to do to create jobs, so the Bundeswehr procurement department was forced to look for an alternative. They found it in the CETME rifle, which was then improved and manufactured by the new company Heckler & Koch.

Jan

#15

Roller-locking with a full-power cartridge in a rifle like the G3 results in a heavy bolt (the bit that looks like a gas tube is in fact a tube for the bolt overhang, thus bad balance. It’s also fiddly to clean and is sensitive to the hardness of the brass - too soft & it binds in the chamber & the case head gets blown off.

H&K have finally dropped it with the G36 & have gone for an AR-18 style (so I’ve heard - not had one apart to look yet!) gas operated rotating bolt.