Jimt r

Note that in the last two terms of equation 2-12, no consideration is given to the overtravel which was allowed in the design. (See fig. 2-3.) The resulting error is so slight that there is no need to complicate the equation further by taking it into account.

Since T' is the total time required for one complete cyclc of operation, the rate of fire in rounds per minute will be:

If it is assumed that the losses arc negligible, the times required for the barrel and bolt to return to the firing position may be determined by the use of equation 2-11 providing that the proper values are substituted for Mr, K, Fo, and D. Making these substitutions and adding the limes gives the time for a complete cyclc as:

M 32.2X240 \COS 240 X .875+55/ — .0660 + .0737 + .0487 = 0.1884 (second)

The rate of fire is then: 60

(This rate of fire is based on the use of springs which absorb all of the recoil energy. As pointed out previously, some improvement in the rate might be gained by using lighter springs and permitting the parts to rebound from buffers at the end of recoil but since such a gain would not be very great, no consideration will be given to this method here.)

With the rate of fire and recoil energy known, the horsepower absorbed by the recoiling parts can be computed by means of the formula:

For the conditions of the example. N is evaluated as follows:

The total weight of the recoiling parts is 50 pounds. The effective weight of the barrel and its related parts will be taken as 40 pounds and the effective weight of the bolt and its related parts will be taken as 10 pounds. Therefore:


The horsepower absorbed by the recoiling parts in the gun of the example will be:

4. Development of theoretical, time-travel and time-velocity curves.

In the design of the various details of the breech mechanism and of the other gun mechanisms such as the feeder and firing device, it is necessary to have information relating to the motion of the recoiling parts during the progress of the cyclc of operation. This information can be presented in convenient form by means of thcorctical curvcs which show the relation between time, the travel of the recoiling

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