Primers

When used in connection with gun ammunition, the term "primer" means the small tube of sensitive explosive which initiates the burning of the propelling charge. Primers are threaded into the base of the cartridge case in case-gun ammunition. For bag guns, the primer is inserted in the primer lock of the breech plug. Priners are classified according to the means of activating them, as follows,

Percussion - impact-fired

Electrical - fired by electricity

Combination - fired by either percussion or electricity

Lock primers: The term "lock" refers to the breech-plug lock of a bag gun; hence, these are bag-charge primers.

Construction: Large-size primers have a main tube, or body; an ignition tube; and a cap, or caps. Activation of the cap, by electricity or percussion, sets off the powder in the ignition tube, which then ignites the powder outside the ignition tube. The ignition tube and the main tube have holes spaced along their length, to provide even burning and ignition over a wider area to the next respective charge.

Percussion caps have a hammer-and-anvil construction to insure impact over a wide area of the explosive.

Electric caps consist of a platinum or other resistance wire "bridge" wrapped with gun cotton. Heat from the bridge ignites the gun cotton for firing.

Charges: The explosive in percussion caps may be a mixture of the following: fulmi-nate of mercury, potassium chlorate, TNT, lead sulfocyanate, antimony sulfide, or pen-taerythritol tetranitrate.

In electric caps, black powder is usually packed with the gun cotton.

For the main charge, black powder or a mixture of black powder and cannon powder is the standard.

Tracers

Tracers are devices designed to leave a trace of either smoke or flame, showing the trajectory of the projectile. They are either screwed or pressed into the after end of the projectile, and may be set into the interior of the projectile, in which case they are inter-nal tracers; or they may project from the end of the projectile, in which case they are called external tracers. Tracers may be ignited by the heat from the burning of the pro-pelling charge, or may be equipped with a striker and detonator which ignites the tracer when the force of set-back occurs.

Some tracers are designed to detonate the explosive charge – "self destruction" – in the projectile when the illuminant material has been burned out by the flame from the tracer igniting a detonator, which, in turn, ignites the main charge.