OVER AND UNDER

Firearms with two barrels placed one above the other.

OVERALL LENGTH

1. Firearm: The dimension measured parallel to the axis of the bore from the muzzle to a line at right angles to the axis and tangent to the rearmost point of the butt-plate or grip.

2. Ammunition: The greatest dimension of a loaded cartridge, i.e., from face of the head to the tip of the bullet for centerfire or rimfire or to the crimp for shotshells or blanks (not to be confused with the uncrimped length in a shotshell.)

OVER-BORE

A shotgun barrel bore diameter greater than the SAAMI maximum for that gauge. Also called a Baker Bore.

OVER-BORE CAPACITY

The point where the powder charge of a particular burning rate of propellant exceeds the capacity of a barrel of specific caliber and length to convert the propellant gas pressure to velocity.

OVERPOWDER WAD

Various designs of separators, made of various materials and used between the propellant powder and the shot pellets.

OVERTRAVEL

The distance after a particular event occurs in the normal operation of the firearm, e.g. additional rearward motion of the trigger after sear or hammer release.

OPEN POINT

A type of bullet having a cavity in the tip or nose.

OPEN SIGHT

A rear sight having a notch through which the front sight is aligned for aiming.

OPERATING HANDLE

Handle of semi or full automatic firearm used to cycle firearm without firing. Also called Charging Handle, Cocking Handle, Cocking Knob.

OPERATING LEVER

On lever action firearms that part operated by the hand to open and close the breech.