(1) Propelling charges consist of a quantity of propellant in a container (cartridge bag for separate-loading and semifixed ammunition) and an igniter and/or primer. The propellant itself is carefully designed for the particular role of the ammunition. Factors considered include chemical composition, grain size, and charge weight. Propellants are described in chapter 1.
(2) In fixed and semifixed rounds, the igniter charge (black powder) is present in the primer. In some models of separated ammunition, an auxiliary igniter charge is placed around the primer or on the distance wadding to assure proper ignition of the propellant. In most separate-loading rounds, the igniter charge is in an igniter bag
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Figure 4-8. Armor-piercing projectile.
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sewn to the base end of the propelling charge. In some designs, the igniter forms a core running through the center of the propelling charge bag. Cartridge-igniter pads are made of tightly woven silk or synthetics to prevent the black powder from sifting through. Cloth used for the igniter charge is dyed red to indicate presence of the black powder igniter. Pads of early manufacture (undyed) are marked IGNITER.
b. Types of Propelling Charge. The type of propelling charge depends upon the type of ammunition (fixed, semifixed, separated, or separate loading) and size of the complete round.
(1) Fixed. The propelling charge in a round of fixed ammunition is loose (or in a polyethylene or polyethylene/rayon bag) in the cartridge case. When the charge does not fill the case completely, a spacer or distance wadding, usually a cardboard disk and cylinder, is inserted in the neck of the cartridge case, between the charge and the base of the projectile.
(a) In semifixed howitzer ammunition, the charge, which is divided into parts or increments for zone firing, is in several cloth bags. The full charge, with all increments in proper order, is in the cartridge case, which is a free-fit over the rear end of the projectile. Each part of the charge is numbered, the base charge being numbered 1. For example, to arrange a 105-mm propelling charge in proper order for firing charge 4, the increments would be arranged in the order 1, 2, 3, and 4, increment 4 being placed uppermost. (For firing less than full charge, all increments above the charge to be fired are removed.) Dualgran. the charge for 105-mm howitzer ammunition, consists of a charge in which a quick-burning propellant of single-perforated grains is used in charges 1 and 2 and a slow-burning propellant of multi-perforated grains in charges 3, 4, 5, 6, and 7. This charge is used with a long primer (no charge-retaining spring required) and incorporates a lead foil in charge 5 as a decoppering agent. Increments are
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