Actions: Recoil Action: Short Recoil Operation - II

In our last post, we studied the basics of a Short Recoil Operated Action, as well as some different weapons that use it. In this post, we will study one more variant of the short recoil operated action, the toggle lock recoil action. This variant of the short recoil operated action was originally used by the world's first machine gun, the Maxim. It was later used in some small arms, notably the Hugo Borchardt designed C93 pistol and later on by the Luger pistol.

The C93 pistol was one of the first successful commercial semi-automatic pistols. Hugo Borchardt was a German born inventor, who later emigrated to the United States, became an American citizen and worked for several well known American firearms manufacturers, including Colt, Winchester and Remington. He later emigrated back to Europe and was employed by the Ludwig Loewe company when he invented his pistol in 1893.

Source: http://www.adamsguns.com

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The pistol was fairly successful, despite the fact that it was mechanically complicated, expensive to produce and hard to handle. Note the almost vertical grip and the big, ugly, semi-circular mainspring hanging out of the back of the weapon. These two features make it harder to aim the pistol quickly and affect the overall balance.

Hugo Borchardt was an easily offended man by nature and he believed that his design was perfect and couldn't be improved. As a result, another employee of the Loewe company, Georg Luger, was tasked with improving the design, which he succeeded in doing in 1896. The Luger design started with the basic Borchardt designed mechanism, but had an angled grip that made it easier to point, added a new grip safety, removed the C93's mainspring and replaced with a leaf spring, improved the balance, redesigned the cartridges used etc. The new pistol was originally adopted by the Swiss army in 1900 and was later adopted by the Germans in 1908. Since the Germans adopted it in 1908, they named it as Pistole-08 or P-08 for short. The words for "zero eight" in German are "null acht", hence this pistol was also known in Germany as the "null acht". The pistols originally used 7.65x22 mm. cartridges, but Luger invented a different sized cartridge for the German army and redesigned the pistol to use this new cartridge: the famous 9x19 mm. parabellum cartridge, also popularly known as the "9 mm. Luger" cartridge. The 9x19 mm. cartridge is still with us today and is the most common military handgun cartridge in use currently.

The Luger was used heavily by the Germans in World War I, produced by both Erfurt Arsenal and DWM (the Loewe company had been renamed to Deutsche Waffen und Munitions Fabriken (DWM) by this time). After the war, the allies restricted production of most weapons for a while, until a German company called Simson was allowed to manufacture Lugers after 1925. Ironically, the Nazis later forced the Simson company to close before World War II, because the owners happened to be Jewish! The Mauser company continued to manufacture Lugers until the end of World War II. Lugers were later replaced in military service by more modern designs, but there are still some private manufacturers making Lugers to this day.

The most distinctive feature of a Luger (and its C93 predecessor) is its toggle lock mechanism. It works similar to the principle of a human knee. Note that a human leg can withstand a lot more pressure when the knee is straight and locked, but once the knee is bent, the leg suddenly becomes much easier to bend after that. The toggle lock mechanism works very similarly. When the weapon is initially fired, the toggle lock mechanism is straight. The recoil causes the barrel and toggle lock initially move back together on rails. Due to the toggle being straight, it doesn't move backwards easily initally. After a little bit of movement, the toggle part begins to ride over a pair of cams that bend the toggle at the joint. Once the toggle lock is no longer straight, it bends much more freely, allowing the bolt to accelerate backwards and recock the weapon. An extractor at the end of the toggle pulls out the old cartridge and ejects it. A recoil spring then pushes the bolt forwards again, whereupon it strips a new round from the magazine and pushes it in the chamber, ready to fire. The movies below show how this works:

This design had a few disadvantages though. For one, it was a fairly complicated mechanism and required precisely fitted parts to work properly. The tolerances required for this design are very tight and parts often had to be hand-fitted for it to work right. These tolerances contributed greatly to the accuracy of the weapon, but took away the reliability. In fact, small amounts of dirt on the exposed firing mechanism parts, especially on the left hand side, could cause the weapon to jam. The Luger was expensive to produce, even for its time, and it was competing in the civilian market with the Colt M1911, which was cheaper to produce and more reliable in operation.

This is why there are no other modern weapons that use this particular variant of the short recoil action mechanism.

Actions: Recoil Action: Short Recoil Operation

In our previous post, we studied the basics of recoil operated actions. In this particular post, we will study one of the types of recoil operated actions, i.e. the short recoil operation.

This action type has a long history, being the action that was used in the first machine gun ever invented, i.e. the Maxim machine gun. It is also the action of choice for most semi-automatic and automatic pixels that use 9 mm. Luger (9x19 mm.) cartridges or bigger. Smaller and lower powered cartridges are used with blowback actions that we studied last month, but once the cartridges get beyond a certain size and power, a blowback action cannot be used any more and most modern pistols therefore use a short recoil operation.

As we noted in our previous post, one of the key differences between a blowback action and a recoil operated action is that a recoil operated action has the bolt (i.e. the metal block that holds the cartridge in the chamber before firing) is locked at the point of firing, whereas a blowback action merely has it held under spring pressure. This enables the recoil operated action to fire heavier cartridges. Also, as we noted previously, in a recoil operated action, some parts of the weapon are allowed to recoil backwards, whereas other parts are held stationary relative to the recoiling parts. In a short recoil action, the parts that are allowed to recoil are the barrel and the bolt.

At the point when the bullet is fired, the barrel and the bolt are locked together and move backwards due to recoil. After a short distance of travel (a few mm. in the case of pistols and a few caliber lengths in the case of machine guns), the bolt and the barrel disengage from each other. How this is achieved is what differentiates various short recoil operation systems. In some cases, the barrel is slowed down, in other cases, the bolt is accelerated. In either case, the barrel stops moving, whereas the bolt continues to move backwards and compresses a recoil spring and also extracts the old cartridge case at the same time, which is ejected via a side port. The recoil spring then pushes the bolt forwards and as the bolt moves forwards, it picks up the new cartridge from the magazine and pushes it and the barrel forwards. When the barrel reaches its forward position again, the bolt and barrel lock again and the weapon is ready to be fired.

As was mentioned above, in some systems, the barrel is slowed down to separate the barrel from the bolt. Weapons that use this include the classic Colt M1911 pistol designed by John Browning, all Glock pistols, Smith & Wesson, FN Browning, SIG Sauer etc.

In the case of the Browning designed Colt M1911, the bolt, barrel and slide all move backwards together initially, but then a barrel link tilts the barrel downwards. As the barrel tilts, the barrel locking lugs unlock themselves from the slide recesses. The bolt and slide continue to move backwards and an extraction claw on the slide also pulls the spent cartridge out of the chamber.

An ejector strikes the back of the spent cartridge and pushes it out of the extraction port, as the slide and bolt continue to move backwards. When the slide and bolt reach the back of the pistol, the recoil spring pushes them forward and during the forward motion, the slide locks back into the barrel and the three pieces then move back together. The two animated movies below show how this works.

In the case of Glock, SIG Sauer and most recently designed automatic pistols, this mechanism is even more simplified. There is a downward inclined ramp attached to the back of the barrel. As the barrel and slide move backwards, the ramp contacts a fixed stud on the pistol's frame. This causes the back of the barrel to move down (and the front to tilt up), which moves it out of engagement with the slide. The rest of the action is similar to what was described earlier. The animation below shows exactly how this works:

In the above three animations, the one thing is common is that the bolt and barrel initially move backward together and are then separated by slowing down the barrel while leaving the bolt and slide free to continue moving backwards.

Another way to achieve this separation is by accelerating the bolt after they both move back together. This mechanism is most commonly used today in the 7.62 mm. and 12.7 mm. M2 machine guns invented by (surprise, surprise) John Browning! The 12.7 mm. M2 is still used in the famous Abrams tank, as well as most other western tanks, which shows the reliability and timelessness of this design. In the M2 machine gun, the barrel and bolt initially recoil together about 10 mm. backwards and then a rotating cam in the receiver disconnects the bolt from the barrel. The barrel has an extension in the back and bottom of the barrel. After the bolt and barrel are disconnected, this extension then strikes a short, curved lever. The lever is pivoted so that it has a mechanical advantage and therefore it pushes and accelerates the bolt rearward. A fixed stud stops the barrel extension, which also halts the barrel, while the bolt continues rearward. As before, we have an animation to show how it works:

We will continue studying short recoil operations tomorrow, where we will deal with some more historical short-recoil operated weapons such as toggle-bolt short recoil actions. It'll be interesting reading!