How semi-automatic pistols function
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This type of small pocket revolver with a folding trigger, was very popular at the end of the 19th century. Semi-automatic pistols at that time were not yet easily available. Most were still in the developmental stage. A revolver has a revolving cylinder or magazine into which several holes or chambers have been drilled to receive cartridges. When facing a revolver, you can tell wether it is loaded or not. If the cylinder is carrying some bullets, their heads will be exposed at the front through the cylinder chambers.
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When the trigger is pulled, or the hammer drawn back, the cylinder is rotated, and the next bullet is brought in line with the barrel. On shooting, the released hammer flies towards the
cartridge primer to strike it. When the primer explodes, the cartridge powder is fired and produce in a very short period of time a great deal of gasses that force the bullet down the barrel at great speed. Semi-automatic pistols do not have a revolving cylinder. The cartridges are held in a removable magazine (also called clip) which, in most cases, is slid and fastened into the handle of the pistol. As a result, it is difficult to easily know whether a pistol is loaded with a magazine. Or even if a magazine installed in the grip really includes cartridges. Now even if there isn't any magazine into the grip, nobody knows if a cartridge is not always chambered in the barrel and the pistol ready to fire. All those features render the use of a semiautomatic pistol more dangerous for a layman.
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As in the Colt Model 1908 shown above, the barrel in semi-automatic pistols is often covered and surrounded by a moving part called slide. To load a cartridge, the slide must be drawn back to its rearmost position by gripping the serrations, and released to fly back under the pressure of the recoil spring, which is often located below or arround the barrel.
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As it moves forward under the recoil spring thrust, the face of the breech, which is an integral part of the slide, strips the top cartridge from the magazine, and ram it into the barrel chamber. The breech is then closed against the firing chamber, and the gun is then ready for firing. On firing, the gas pressure drives the bullet down the barrel, and at the
same time it will also drive the cartridge case against the breech which, in turn, drive the whole slide rearward. At the end of the rearward travel of the slide, the later will be driven forward under the push of the compressed recoil spring. And a new cartridge will be automatically chambered. The term semi-automatic refers to the way a pistol is fired, and not the way the cartridges are loaded. Automatic firing occurs when the bullets are loaded and fired in a continuous stream as long as the trigger is kept pulled. Like a machinegun for instance. With a semi-automatic firearm the shooter has to release the trigger after each shot, or firing cycle, before another cycle can begin. Technically speaking, it is incorrect to use the term "automatic pistol" when referring to a semi-automatic pistol. The design and working of a revolver is simple and straightforward when compared to the design and functioning of semi-automatic pistols. With semi-automatic pistols, some mechanical challenges have to be solved when increasing the power of the cartridges used. The design and workings of a pistol using a .25 ACP cartridge is different from that of a model firing the powerfull .45 ACP. When the cartridge size approaches .38 caliber (9 mm), it is hazardous to use the weight of the slide only as counterpart to the forces generated by the explosion. When the gasses pressure nears one Ton/cm2, the slide becomes a dangerous missile aimed toward the shooter's face. To cope with this issue, the breechblock and the barrel needs to remain locked together until the bullet leaves the barrel, and the gas pressure drops to zero. Many firearm designers As John Browning or Georg Luger proposed technical solutions that made their fame in the field of firearms. Among the most original systems was the toggle lock initiated by Hugo Borchardt and greatly improved by Georg Luger. The Luger pistol, in its achieved form, date back to 1898 and remained in service in Germany until the end of World War II. Swiss kept it as a regulation sidearm for many more years. In the Luger pistol, the locking and unlocking of the breechblock is controlled by the use of a toggle mechanism.
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The breechblock is mobile and travels within a long U shaped barrel extension that is screwed onto the end of the barrel.
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The breechblock is "loosely" attached to the forward arm of the toggle by the use of pin. That allows the toggle pieces to fold up and down while the breechblock moves back and forth inside the barrel extension.
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In
the closed position, with the two toggle links flat, the barrel extension with the breech block and toggle act as one bound unit. This state remains unchanged as long as the center of the mid-axis is under the line that joins the centers of the external axes.
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Upon firing, the thrust of the burning gasses drives the whole unit quickly to the rear. During the initial move of about 6 mm, the bullet has enough time to leave the barrel, and the pressure will drop to zero. The unit however, continues rearward under its momentum, and the toggle knobs engages the slopes on the frame (green arrow).
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As the knobs climb the slopes, the toggle is mechanically induced to fold, and draw the breechblock backwards because of its pin-connection. The extraction and ejection of the case also take place during the cycle.
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When the toggle folds, the recoil spring which is attached to the toggle rear arm by a link is compressed. When the toggle is completely folded, the recoil spring drives it forwards. This forward move causes the breechblock to strip a fresh round out of the magazine, to chamber it, and lock the pistol. The firing cycle is then complete.
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