Note that the .256-140 crosses the curves of those having a higher velocity, but a less value for C. A more extended study of the velocity and energy curves will show that THE projectile having the greatest efficiency may be determined and that it has its maximum and minimum. See Experimental and Research Work, Vol. 11. The resistance of the atmosphere is computed by the formula in which R, is the resistance, in pounds, the values of A and n are taken from the preceding table, d the effective diameter, c the coefficient of reduction, and g=32.16. Using the .30-150-2700-C-.389 and c .595 That is, the resistance of 1.447 lbs. would, if it remained constant for one second, diminish the velocity of the projectile by 2176 f.s. The values of A and n in formula 10b are determined as follows, Rt = (V2 v2) 2 s For. 10c in which R is the retardation in foot seconds, V the velocity at the beginning and v the velocity at the end of a measured path, s the length of that path in feet, which should be so short that the resistance may be considered uniform over the entire path. Formula 10c premises experiment. Rs Rt X w For. 10d in which R, is the resistance in pounds, w the weight of the projectile in pounds, and g=32.16 Substituting the known values of d, g, R, (determined by formula 10d), and c (either given or determined by formulae in Chapter V) in formula 10a, the values of A and n are computed. CHAPTER V. c, the Coefficient of Form or Reduction. IS the coefficient of form or shape, or as called C by some authorities the coefficient of steadiness, and in its broadest meaning it includes not only the form or shape of the head, but its steadiness of flight depending upon the velocity of translation, its rotational velocity or spin, its obliquity to the tangent of the trajectory, the distribution of its mass, and generally upon all the causes on which depend the movements of precession and nutation. In formula 9, w and d are readily determined by measurement, therefore C depends upon c for its value, which means that a small error in the value of c will produce an inverse corresponding error in the value of C, and thus the ballistic properties of the projectile misrepresented. Fortunately, the value of c may be determined with considerable degree of accuracy. in which n is the radius of the ogive expressed in diameters of the projectile, and k the algebraic sum of errors due to the construction of the projectile and its steadiness and obliquity in flight, for the projectile does not fly point on in all parts of its path, as seen in Fig. 1. The errors in the construction of projectiles are usually in the weight, the diameter or the point or in all. These errors varying to an indeterminable degree, k is invariably found by experiment. However, its value is usually unity, and when so, does not affect the value of c. Before c can be computed, n must be determined. It can be with a great degree of accuracy by measuring the diameter and length of head of the projectile with a micrometer and substituting in the formula n = 4L2 + 1 For. 12 in which L represents the length of the head expressed in diameters of the projectile. Since C is determined with the greatest accuracy by experiment, using formula 10, c may be com |