| Summary: | <p>The paper considers, in the classical treatment of an artillery shot, a pyrostatic (preliminary) shot period during which a projectile is assumed to be motionless until the pressure of the powder gases becomes equal to the conditional shot-start pressure. The latter is determined by the maximum force of resistance to the driving band completely engraved by rifling, with resistance related to the projectile cross-section area. In actual practice, the engraving is a gradual process (in this case the shot period is called a forcing one). A level of the axial inertial forces may even be sufficient for fuse arming of inertial safety devices.</p><p>The fact that there is a need to have a sufficiently large set of the appropriate design and physical parameters, which are, usually, incompletely known, hinders the use of a rigorous calculation technique.</p><p>To simplify the inter ballistics calculation, an analytical approximation of the engraving curve is proposed. For its description it is necessary to know the maximum force of resistance (or the shot-start pressure), the width of the driving band and the total travel of a projectile when engraving. Thus, it is assumed that after complete engraving of the driving band the resistance super-quickly drops to zero, and an appropriate jump in the acceleration (setback) curve of the projectile occurs.</p><p>For the first time, it is proposed to include the number of inter ballistic parameters into the work of powder gases, thus ensuring an automatic integration of the system of equations regardless of the specific description of the engraving curve (in some cases, analytical integration needed for calculation may be impossible).</p><p>The example of calculation for the 122-mm D-30 howitzer illustrates a practical application of the proposed technique. Comparison of calculation results using the traditional and proposed techniques is made to show that the integral characteristics of the shot are close. It is found that a progress of the engraving process is relatively slow, and a level of the maximum resistance force is reached almost at the very end of the forcing period. It should be noted that the pressure in the firing chamber can many folds exceed the forcing one. An available specific "S-shaped" initial section of the acceleration (setback) curve of the projectile is revealed, which is confirmed by experiments. The final values of the ballistic parameters are close to those obtained by a more rigorous technique.</p>
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