Foregrip

A vertical forward grip is a vertical grip that is designed to attach to a firearm for the forward hand (or "off hand"). These aid in the maneuverability of the firearm, since the natural angle of a person's outstretched hand is more oriented to grasping objects at a vertical angle, rather than a horizontal one perpendicular to the body. Foregrips can decrease accuracy in precision rifle shooting if the shooter tends to "muscle the weapon".

Angled forward grips can provide similar functionality to vertical forward grips. One such popular product is the MagPul Dynamics AFG, or Angled Fore Grip. This allows the operator to lay the palm of his or her hand onto the grip while pushing the thumb down on the top of the gun.

A shorter version is referred to as a "Stubby grip", primarily intended to keep the shooter's hand from moving forward of the muzzle.

The legality of vertical foregrips on pistols in the United States is unclear. In the United States, firearms are categorized by the National Firearms Act and firearms manufactured with specific features are subject to restrictions and controls. In the case of a vertical forward grip on a pistol, the law does not explicitly define such a feature as belonging to any category.

In May 1993, in response to legal action brought by the Bureau of Alcohol, Tobacco, and Firearms (ATF), the South Carolina District Court's finding of fact concluded that a pistol modified with the addition of vertical fore grips was still a pistol and not an any other weapon device. Following this, the ATF dropped their charges and the case was not tried; as such no precedent was set.

In an open letter sent to Federal Firearms Licensees in April 2006, the ATF stated their interpretation of the law; that installing a vertical forward grip on a handgun is the same as manufacturing an Any Other Weapon (AOW) category firearm and subject to registration and taxation, with significant penalties for manufacturing or possessing such an unregistered weapon.

The ATF has stated that angled grips do not make an AOW from a handgun.

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Wikipedia