It is truly amazing to realize that this amount of smokeless powder would more than fill two large feed-sacks and that it is burned at such a rate that it all would be consumed in one minute inside a steel cylinder which weighs only about 50 pounds and is less than one foot long. The rate at which thermal energy is released in firing a weapon of this type is tremendous, particularly when the relatively small physical dimensions of the cylinder arc taken into account.

During a sustained burst, the cylinder of a high-ratc-of-firc rotary action mechanism absorbs enough which can be fired over a given period, or requires the development of an effective method of cooling the cylinder. Cooling by normal air flow around the cylinder is not likely to be successful, particularly becausc a large portion of the cylinder is usually covered by the other parts of the gun. The fact that the cylinder revolves will probably make the use of jacketing and liquid coolant impractical. One method of cooling which can be used is to spray a refrigerant gas through the chambers after the fired cartridge is ejected. Further heat removal could be accomplished by using the same means to cool the outside of the cvlinder. In anv ease, the

cooling system used for the cylinder will be the major factor affecting the ability of the gun to deliver a high volume of fire.

The third problem which has proved to be a stumbling block in the development of high-rate-of-fire minimum wall thickness

Figure 4-12. Effect of Space Required for Piston Seals.

safe wall thickness

Figure 4-12. Effect of Space Required for Piston Seals.

heat to cause its temperature to rise quite rapidly. F.ven with bursts of moderate length fired at intervals, the heat will be retained in the cylinder between bursts and can build the temperature up to the danger point in a relatively short period of time. When the temperature, of the cylinder reaches a level of from 600° to 300° F., it is possible for a "cook-ofT1 to occur. This condition is particularly dangerous in a rotary action weapon because of the fact that the gun may stop firing with live cartridges in chambers which are not aligned with the barrel. If these cartridges should cook off, the results would be disastrous.

The heat problem in high-ratc-of-fire rotary-chamber mechanisms is so critical that it cither places a severe limitation on the number of rounds rotary action cannon is the requirement for high precision in the cylinder indexing mechanism. This problem arises because of the necessity for maintaining a very accurate alignment of the chamber with the barrel bore at the instant the gun is fired. In revolver hand guns, this same alignment requirement exists but is much less critical. With low velocity-bullets made of soft lead, a small misalignment is not too serious because the worst that can happen is that the gun will shave some lead and the accuracy of fire may be upset. However, in aircraft cannon, the cffect of misalignment can be very dangerous. If the chambcr and barrel bore are not concentric within 0.005 inch, it is likely that the rotating band of the projectile will be sheared off. This will not only cause the flight of the projectile to be very

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