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Functions for Calculating the Retardation of Standard Projectiles

Retardation is calculated according to the formula R = Avm , where R is the retardation of the Standard projectile under standard conditions, v is the velocity of the projectile and values of A and m are shown in the tables below. To find the Ballistic Coefficient, C, it is necessary to use the value of R in the formula C = R/r, where r is the measured retardation of the projectile under test. In practice, 2 values for R are derived from the measured Initial and Final velocities of the test projectile, the mean being used to find C. Values for A and m change with velocity, since the drag forces, acting upon the projectile, vary with its velocity. These velocity ranges, as well as the functions associated with them, differ slightly according to the data from which they were derived. The, British conducted, firing tests, between 1904 and 1906, provide the basis for the retardation functions in the first table. The second table shows those used to formulate the American Ingalls’ Tables, derived from Krupp’s firings of 1881 and the work of Mayevski.


 

British Functions for Retardation of their 1904-1909 Standard Projectile

Velocity Range (fps)

Value of

A

Value of

m

From

To

1

839

7.4422 x 10 - 4

1.6

840

1039

5.9939 x 10 - 8

3

1040

1189

2.3385 x 10 - 18

6.45

1190

1459

9.5408 x 10 - 8

3

1460

1999

5.9814 x 10 - 4

1.8

2000

2599

5.8494 x 10 - 3

1.5

2600

4000

1.5366 x 10 - 3

1.67

Mayevski / Ingalls Retardation Functions for Krupp's 1881 Standard Projectile

Velocity Range (fps)

Value of

A

Value of

m

From

To

1

789

4.6762 x 10 - 5

2

790

969

5.9353 x 10 - 8

3

970

1229

6.3368 x 10 - 14

5

1230

1369

9.5698 x 10 - 8

3

1370

1799

1.3160 x 10 - 4

2

1800

2599

1.2480 x 10 - 3

1.7

2600

3600

4.0649 x 10 - 3

1.55

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