The present invention relates generally to propellant charges in medium and large caliber cased or caseless gun systems. More specifically the invention is directed to the configuration of the charge that is loaded into the cartridge case assembly. The configuration, in this case, generally the shape, density and placement of the propellant charge is a departure from contemporary configurations.
Munitions that use solid propellants carried in the cartridge casing typically relied on spherical or cylindrical grain geometry for ease of processing. Burn rates, the speed that a flame front is propagated through the propellant, were controlled through geometry (i.e. grain perforations) or through chemical (i.e. deterrents) means. Burn rate modification and progressivity tuning are important considerations in designing charge loads. Another technique to provide a propellant in the cartridge is to use what are known as co-layered propellants in a disk or rolled scroll. Co-layered propellants being a descriptive term describing the use of layers of precut propellant elements cut from a sheet of propellant material. It is known to use co-layered propellants in the shape of rings or appertured disks of different propellants stacked in a sandwich configuration. In co-layered propellants so called "fast burn" propellant sheet stock, cut in the appropriate appertured disk or ring shape, is sandwiched between two layers of slower burning propellant sheet stock. The source of co-layered propellant sheets is Alliant Tech Systems who can provide the co-layered propellant in die-cut annular ring shapes or in uncut sheets.
Another use of co-layered propellants is in a rolled scroll form. In this configuration the propellant sheet is rolled to form a scroll. The scroll form is aligned longitudially with the boom of the projectile and if ignited from the end of the scroll, the normal technique, the flame propagation will be more difficult to control than the flame propagation of this invention. In the scroll form of propellant it is difficult to control burn propagation and there is a risk that waves of pressure may build to the point of weapon destruction. Therefore the scroll form of propellant is more difficult to specify than is the strip embodiment presented here.
One of the disadvantages of co-layered propellants is that the stacked disks provide, having only limited natural ullage, a barrier to gas flow which can lead to detrimental pressure waves in the gun. These detrimental waves are caused in part by the blockage presented by the disks. The invention presented in this specification avoids or minimizes the barrier to the gas flow as the strips of propellant allow sufficient ullage between the strips.
Another disadvantage of co-layered propellants in disk form, as is used in the prior designs, is that the manufacture of the rings creates a large amount of scrap propellant. It is known that to cut a circular disc from a rectangular sheet of propellant material will cause significant selvage or waste of material. The sheets of propellant are expensive and anytime you can save on material the cost of a loaded cartridge case will be commensurately lower.