Pressure Effective On Base Of Cartridge Case

Figure 4-11. Effect of Piston Seal on Force Applied to Revolver Frame.

much stronger and heavier frame structure than if the piston seals were not used.

Depending on the form of the ammunition fired by the gun, it is possible that the presence of the piston seals may result in a further design disadvantage. In designing the cylinder of a revolver machine gun, it is desirable to space the chambers as closely as possible by keeping the walls between the chambers at the minimum safe thickness. A compact arrangement, such as is shown in fig. 4-12A, makes it possible to hold the cylinder to a small diameter and to minimize its weight and inertia. This not only makes for a less bulky weapon, but also decreases the power required for operation and lessens the strain on the rotating mechanism.

bottle-necked, there may be ample metal for accommodating the seals at the forward end of the cylinder even when the chambers are spaced as closely as possible at the rear.

The preceding paragraphs are concerned with the problem of gas leakage in full automatic rotary' action machine guns. The next important problem for consideration is caused by the great amount of heat absorbed by the cylinder during long bursts at the extremely high rates of fire being attempted with modern rotary action cannon. The magnitude of this problem can be illustrated readily by one rather startling fact. The ammunition used in one modern 30-mm revolver gun is loaded with a 1060-grain propellant charge and the gun is designed to fire at

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