= 446 (rounds per minute)

With the rate of fire and bolt energy known, the power absorbed by the bolt can be computed by means of the formula:


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

i94X440 33,000

This should be adequate power for operating the gun mechanism.

4. Development of theoretical time-travel and time-

velocity curves

The theoretical curves showing bolt travel and bolt velocity with rcspcct to time for a gun using advanced primer ignition are developed according to the same general principles employed for plain blowback but there are certain differences in the details as a result of the fact that ignition of the primer occurs while the bolt is still moving forward.

The development of the curves starts with the free bolt velocity curves (figs. 1-24 and 1-25) which are derived directly from the free bolt momentum curve previously plotted (fig. 1-23) by-dividing cach ordinate of the momentum curve by the mass of the bolt. (Bolt weight is 26 pounds.)

Fig. 1-26 shows the time-travel and time-velocity curves obtained for the gun of the example for the period from t—0 to t=0.010 second. These curves


Figure 1-29. Velocity-Displacement Graph were derived by the step-by-step system described under plain blowback and the steps referred to in the figure are those in the procedure described for plain blowback. Note that for the first 0.0009 second the bolt travel curve dips downward to zero and then starts to rise as the bolt moves back, indicating that the bolt travel is measured from the most forward position reached during the propel-lant explosion. In this particular design the total velocity loss resulting from the effect of the initial spring compression during the time interval between t=0.0009 to t—0.010 is equal to 1.47 feet per second, computed as follows:

The loss due to the spring constant K, as determined by the method of step 4 is only about 0.19 feet per second. This loss is so slight that it is not necessary to continue the process of successive approximation any further than step 5.

The remainder of the bolt displacement cum can now be determined analytically by using equation 1-10, modified as necessary to account for the displacement d' during the first 0.010 second. The changed values to be used in equation 1-10 are the following:

Fc'—F0 | Kd' = 130+247 X. 150 =168.5 I)' = D — d' — D —. 150 t/ = t—.010

Making the required substitutions as explained for plain blowback gives the final form of the equation to be used after the first 0.010 second as:

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