Gun Rule

The gun rule is a type of slide rule for calculating the correct tangent elevation (TE) for a given range, charge and muzzle velocity (MV).

Definitions Gun rules specific to a particular gun type were issued with that ordnance. For example the BL 5.5-inch gun was issued with two gun rules that differed in the power of the explosive charge that carried the projectile away from the gun - the No. 2 for use with the 80 lb projectile, charges four and super, and the No. 3 for use with charges one, two and three.

Gun rule for the BL 5.5-inch gun.
The top line of figures (Tangent Elevation degrees) runs from 4 to 45.
The second line of figures (Range hundreds of yards) runs from 15 to 85.
The lower line of figures (Muzzle Velocity) runs from 2100 to 1500 feet per second.
Click the image to view an enlargement.

Circular gun rules were also used, as shown in the photograph.

References:
User handbooks - 25-pr, BL 5.5-inch, 105-mm
Artillery Training Volume III Pamphlet 1
Course notes (various), School of Artillery, Waiouru.

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