In
breechloading firearm
A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions).
The first firearms originate ...
s, primary extraction is the initial phase (the first few millimeters) of the
extraction of a spent
casing from the firearm
chamber. After the primary extraction comes the secondary extraction where the bolt is moved further backwards, and the extraction is then normally finished with the spent cartridge being ejected.
The first few millimeters of extraction tend to require a much higher peak
force
In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...
than the rest of the extraction due to the spent casing sticking against the chamber walls. The case is not chemically sticking as it still rotates with the bolt, gripped by the extractor claw on the rim. The mechanical sticking effect is a result from the case having expanded due to the high pressures during firing, and the extra initial force required can, depending on firearm design, make the extraction difficult for the user. Selfloading rifles usually don't have a separate motion for primary extraction, but instead depend on using a lot of force in order to start the extraction.
Different designs are used for ensuring reliable extraction in manual mechanisms, with most of them being based on the principle of
mechanical advantage. The camming action seen in many
bolt-action
Bolt action is a type of manual Action (firearms), firearm action that is operated by ''directly'' manipulating the bolt (firearms), turn-bolt via a cocking handle, bolt handle, most commonly placed on the right-hand side of the firearm (a ...
rifles is an example of mechanical advantage being used for chambering and extraction. There are examples of some firearm designs being less successful due to poor design around the primary extraction, which can result in a stuck case in the chamber. Notably some
pump
A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic or pneumatic energy.
Mechanical pumps serve in a wide range of application ...
and
straight pull mechanisms are perceived as having the advantage over bolt actions that they are faster and require fewer body movements to operate by the user, however, they are often more complex than traditional bolt action designs, and often have little or no primary extraction
[Swiss Straight-Pull First Impressions – Forgotten Weapons](_blank)
/ref> lacking the mechanical advantage of a turn bolt which can lead to stoppages. There are some examples of straight pullrifle
A rifle is a long gun, long-barreled firearm designed for accurate shooting and higher stopping power, with a gun barrel, barrel that has a helical or spiralling pattern of grooves (rifling) cut into the bore wall. In keeping with their focus o ...
design has been reported to have no issues with primary extraction.Blaser R8 , Straight-Pull Rifles Reviews , Gun Mart
/ref> In this design, the bolt head moves in a purely linear motion, and except for the bolt handle cam when opening or closing the action, operation by the shooter is also purely linear. The Heym SR 30 is another successful straight-pull design which features a bolt with ball bearings as locking elements. Here the primary extraction is performed by retracting the bolt handle, which uses leverage from the opposite side of the bolt to swing the handle to the open position, giving a mechanical advantage.
See also
* List of straight-pull rifles
* List of pump-action rifles
References
External links
Article: Primary extraction timing on Remington 700 - LongRifles, Inc.
Video: Different types of primary extraction and how they work
Video: Demonstration of primary extraction on a Remington 700
Firearm terminology