IRON SIGHT

Any sight, front or rear, not containing optical magnifying elements. It may be fixed or adjustable. Also called Metallic Sight.

INTERIOR BALLISTICS

The science of ballistics focusing on all thermochemical and physical events from primer ignition through projectile exit from the muzzle.

IRON FORE-END

On firearms with a one-piece stock, an intermediate part that holds the wood against the barrel and frame and retains the latch mechanism.

IGNITION TIME

The elapsed time from moment of firing-pin contact on the primer to the point on the X (time) axis equal to the point where the pressure time curve indicates propellant burning has initiated.

IMPRESSED CHECKERING

A heated die process which produces a carved effect in the gun stock or forearm.

IMR POWDER

The abbreviation for Improved Military Rifle Powder. A single base, tubular, smokeless propellant.

IN BATTERY

A firearm is said to be “In Battery” when the breeching mechanism is in the proper position for firing.

IN LINE

A firearm design incorporating it’s firing mechanism substantially in line with the longitudinal axis of the barrel. Ignition gases are typically induced concentric to the bore with this design.

INDUSTRIAL CARTRIDGE

1. Usually a blank cartridge used in industrial applications such as stud drivers. Usually color coded to indicate power level. Also referred to as power tool cartridges and power actuated tool cartridges. 2. 8 Gauge industrial loads with single projectiles or buckshot used for cleaning continuous cement kilns and other industrial applications.

INERTIA BLOCK

1. A device intended to function during recoil to set the fire control mechanism to fire a second barrel. 2. A device intended to function during recoil to prevent doubling on some double barrel shotguns.