Pistol grip (on right) of the SIG SG 550 (protruding)
Stock with semi-pistol grip on a Finnish M39 Mosin–Nagant rifle.
Straight or English stock (non-pistol grip) on a Soviet M38 Mosin–Nagant carbine.
On a firearm or other tool, the pistol grip is that portion of the mechanism that is held by the hand and orients the hand in a forward, vertical orientation, similar to the position one would take with a conventional pistol.
For firearms, the pistol grip is generally used by the hand that operates the trigger. Rifles and shotguns without pistol grips are generally referred to as having "straight" or "upland" (shotguns only) style stocks. Some firearms, such as some versions of the Thompson submachine gun, have a forward pistol grip which is used to stabilize the firearm in operation. The pistol grip often serves multiple functions such as a magazine housing, bipod, or tool storage. In some firearms, like the Finnish light machine gun Kk 62, the pistol grip is also used as a handle to charge the weapon.
Pistol grips are a defining feature in United States gun law. A forward pistol grip on a pistol is restricted under the National Firearms Act. Pistol grips which protrude below the weapon and are not integrated with the shoulder stock (i.e. as part of a thumbhole stock) are currently regulated in some states and was regulated by the now expired Federal Assault Weapons Ban.
Tools with pistol grips run the range from hand saws to pneumatic nailers. Often the word "gun" appears in the name of pistol-gripped tools such as the glue gun, caulking gun and nail gun. A number of tools, like firearms, have a forward pistol grip. Drills and grinders often include this feature for added control.
One of the reasons the pistol grip style is so common in machinery is because it is possible to ergonomically position the operating controls. For example, on the AR-15 and M16 rifle, a right handed user's index finger can control the trigger and magazine release, while the thumb can control the safety or fire mode selector switch, all without needing to remove the palm from the grip.
The original article can be found at Pistol grip and the edit history here.