Shooting USA | Handgun Operation: Semi-Automatic Safety Mechanisms
Semi-automatic gun safety systems can take on a dizzying variety. The best known are probably the swiveling thumb levers on the frame or slide. Sometimes these are only on the left; however, in many newer designs, they are double-sided for ambidextrous use. While many thumb locks pivot down to release, some work in the opposite direction. Such frame-mounted fuses typically block the firing pin, while those that are sled-mounted usually prevent the hammer from touching the firing pin.
The manual safety on this Taurus TX22 Competition is in the firing position.
Another type of safety system found on some traditional double-action pistols is the hammer drop safety system, also known as a decocker. When it engages, the hammer falls into its lowered position without damage. With any pistol of this type, the hammer remains in the cocked position when you fire a shot or simply pull the slide to insert a cartridge into the chamber. Since such pistols are not designed to be safely carried with a cartridge in the chamber and the back of the hammer, the hammer must be lowered before the pistol is holstered, placed in a pistol box, etc. The relaxation mechanism does this safely. Semi-automatic pistols with only double action can have a thumb safety device or, alternatively, no active safety mechanism at all.
All semi-automatic pistols usually have one or more passive safety systems, such as unless the trigger is pressed.
Semi-automatic operating cycle
All semi-automatic guns have essentially the same duty cycle. However, some steps in the cycle may not apply to all types of actions. For example, semi-automatic guns with only double action do not have a “cocking step”.
- Burn. Pulling the trigger triggers an internal or external hammer that strikes the firing pin and fires the cartridge, or it can release a cocked, spring-operated firing pin or firing pin in the breech.
- Unlock. The lock pattern is determined by the type of semi-automatic mechanism. In recoil-actuated actions, mechanical cam surfaces are used to unlock the barrel from the breech after the two components have traveled a short distance backwards. Gas powered actions use gas pressure drawn from the bore to propel the slide rearward and unlock the action. Blowback powered systems are by definition unlocked, so no unlocking is required. In such systems, the action simply opens when the gas pressure in the chamber and bore overcomes this forward force of the return spring and the inertia of the slide or bolt.
- Extraction. A claw extractor attached to the sliding surface engages the edge of the cartridge case and, after unlocking, pulls it out of the cartridge chamber.
- Expectoration. As the slide moves backwards with a used cartridge case, an ejector – usually a standing blade mounted in the frame – touches the case head and ejects the case through the ejection opening.
- Tighten. At or near the extreme rear limit of its stroke, the reciprocating slide cocks the hammer or beater, which is held backwards against spring tension by the release mechanism.
- Feeding. The compressed return spring quickly pushes the slide forward, pulls a cartridge out of the magazine and inserts it into the chamber.
- Locking. In semi-automatic designs with the buckle closed, the locking action occurs during the last fraction of an inch of the forward motion of the buckle. In the vast majority of designs, the back of the barrel is pushed up as it moves forward so that its locking surfaces engage the breech or frame and lock the action. In the case of blowback-operated versions, there is no blocking; the momentum of the advancing bolt or bolt is sufficient to completely chamber a cartridge and close the system (at which point the system is said to be in the battery). Only the force of the compressed closing spring combined with the inertia of the bolt or slide will keep the action closed.
Read more: Gun Operation: Types of Gun Actions