Cartridge cases

Propellant charges for small- and medium-caliber guns are assembled with primer and powder enclosed in a brass or steel container, or cartridge case. This assembly of the entire charge is a single, rigid, protecting case increases the ease and rapidity of loading and reduces the danger to personnel from flare-backs. On the other hand, additional care in handling must be exercised with this type of ammunition, since the cartrdige case contains the powder charge and the primer.

Fixed ammunition: Guns of smaller caliber use "fixed ammunition", with the cartridge case firmly crimped to the base of the projectile. The following guns employ fixed ammu-nition: 20-mm, 40-mm, 1.1-inch, 1-pdr., 3-pdr., 6-pdr., 3"/23, 3"/50, 4"/50, and 5"/25.

Semi-fixed ammunition: Guns of larger caliber, for ease of handling, require separa-te loading of powder and projectile, or "semi-fixed ammunition". With this type of ammu-nition, the powder and primer are contained in a cartridge case, but the case is not crim-ped to the projectile. In semi-fixed ammunition, the powder is held firmly in place by a cardboard spacer and/or a cork closing plug. The following guns employ semi-fixed am-munition: 5"/38, 5"/51, 6"/47, and 8"/65.

Gas seal: Beside affording a safe and convenient method of loading, the cartridge case also prevents the escape of gases through the breech of the gun. The cartridge case has a fairly snug fit in the gun chamber and forms an effective gas seal by its ex-pansion when the gun is fired.

High-Capacity, Reduced, and Target charges: To provide more flexibility in fire control when a variety of projectiles is used, a special charge is assembled for use with the light high-capacity projectiles and is known as a "high-capacity" charge. These char-ges contain less powder than their corresponding full charge. Also containing less pow-der, but designed mainly for reducing wear on gun chambers in target practice are the "reduced" and "target" charges. Weights and sizes of these particular charges are found in the table of "Existing Service Rounds" accompanying this chapter.

Short cases: When a round fails to be seated fully on ramming into the gun chamber, thus preventing closure of the breech, the projectile can still be fired by extracting the full-sized case and loading a "short" case. These are merely shorter models of regular cases. Their sizes and weights are included in the table of "Cartridge Case Specificati-ons".

Special cases: Aside from the service-loaded, reduced-charge, and "short" cases, certain special types are also in use. These include saluting charges for 3"/23 and 1-, 3-, and 6-pounder guns; impulse charges for torpedos, depth charges, and projector char-ges; and charges for line-throwing apparatus. These cases will not be described in this publication, since they are not primarily concerned with projectiles.