GENE SLOVERSUS NAVY PAGES USN RANGE TABLES COLUMN 11 |

17B5 Column 11

Column 11 is headed “Change of range for variation of -1 pound in weight of projectile.” This change of range is due to two

causes which are opposite in their effects. The first is the change in the initial velocity. A projectile heavier than standard will

be expelled from the gun at lower than designed muzzle velocity, causing a decrease in range. However, increase in weight

will cause an increase in value of the ballistic coefficient and, since retardation varies inversely as the value of the ballistic

coefficient, this causes an increase in range.

Referring to the range table in appendix C, part 2, it is seen that at short ranges, the effect on initial velocity is the predominant

factor, while at long ranges, the effect on ballistic coefficient has the greater significance. At a range of 6,700 yards (in this table)

the effects exactly cancel each other and the net error is zero.

In practice column 11 is not normally used aboard ship. It would be used if projectiles of other than standard weight were

to be fired. Projectiles are required to be of designed weight within small tolerances, and the effects of these small variations

are neglected, since it would obviously be impracticable to weight each projectile or to make a correction for each gun before

firing each salvo. It is apparent, however, that this variation in projectile weight is one reason why all shots of a salvo, fired at the

same time and under the same conditions, do not fall at the same point.

EXTRACTS FROM 5”/38 RANGE TABLE

EXTRACTS FROM 8"/55 RANGE TABLE

Column 11 is headed “Change of range for variation of -1 pound in weight of projectile.” This change of range is due to two

causes which are opposite in their effects. The first is the change in the initial velocity. A projectile heavier than standard will

be expelled from the gun at lower than designed muzzle velocity, causing a decrease in range. However, increase in weight

will cause an increase in value of the ballistic coefficient and, since retardation varies inversely as the value of the ballistic

coefficient, this causes an increase in range.

Referring to the range table in appendix C, part 2, it is seen that at short ranges, the effect on initial velocity is the predominant

factor, while at long ranges, the effect on ballistic coefficient has the greater significance. At a range of 6,700 yards (in this table)

the effects exactly cancel each other and the net error is zero.

In practice column 11 is not normally used aboard ship. It would be used if projectiles of other than standard weight were

to be fired. Projectiles are required to be of designed weight within small tolerances, and the effects of these small variations

are neglected, since it would obviously be impracticable to weight each projectile or to make a correction for each gun before

firing each salvo. It is apparent, however, that this variation in projectile weight is one reason why all shots of a salvo, fired at the

same time and under the same conditions, do not fall at the same point.

EXTRACTS FROM 5”/38 RANGE TABLE

EXTRACTS FROM 8"/55 RANGE TABLE