PRACTICAL GUNNERY.
1. How may the velocity of a shot or shell be ascertained?
Approximately by the empirical formula,
( _ac_ )
_V_ = 1600√(————— ).
( _w_ )
Where _V_ = initial velocity.
_a_ = a coefficient, whose value depends on the windage.
_c_ = charge }
_w_ = weight of ball } in lbs.
The values of _a_ are:
Windage. Values of _a_.
0.175 3.6
0.125 4.4
0.090 5.0
2. Does a shot or shell continue at the same uniform velocity during
its flight?
The velocity decreases as the distance increases, in a proportion a
little higher than the squares of the velocities throughout.
3. What causes a decrease in the velocity of a shot?
The resistance of the air, which varies as the square of the velocity
of the shot.
[Sidenote: 148]]
4. With balls of different diameters, and equal velocities, to what is
the resistance of the air proportional?
Their surfaces, or the squares of their diameters.
5. Would the velocity of the shot be increased by lengthening the gun?
Only up to a certain point; in a proportion which is nearly the mean
ratio between the square and cube roots of the length of the bore. It
is found that the velocity given by long guns is reduced to an equality
with that of short guns within a short distance from the muzzle when
fired with similar charges.
6. Would the velocity of a shot be increased by entirely preventing the
recoil, or by adding greatly to the weight of the gun?
In neither case would any sensible effect be produced on the velocity.
7. Would the velocity of the shot be increased by using a larger charge
of powder?
Only to a certain point, peculiar to each gun; by further increasing
the charge the velocity would be gradually diminished; yet the recoil
is always increased by an increase of charge.
8. What is the ratio of the velocities of shot, when of different
weights, but fired with similar charges?
The velocities are inversely as the square roots of their weights.
9. What is the ratio of the velocities of shot of equal weights when
fired with different charges of powder?
The velocities are directly as the square roots of the charges.
[Sidenote: 149]]
10. How may the velocity be increased without augmenting the charge of
powder?
By decreasing the windage; the loss of velocity by a given windage
being directly as the windage. From 1-8 to 1-12 is lost by a windage of
1-40 diameter.
11. What is meant by the time of flight of a shot or shell?
The time during which it is passing through the air from the piece to
the first graze.
12. When firing with common shells at 45° elevation, how is the time of
flight found?
Extract the square root of the range in feet and divide by 4, or divide
the range in feet by 16 and extract the square root of this quotient.
NOTE.—Range in feet = ½_gt_² × cotangent elevation.
= 16_t_² × cotangent elevation.
= 16_t_² where the elevation is 45°.
_______________________________
Or _t_ = ¼√range in feet for elevation 45°.
13. Having the time of flight, how is the range ascertained?
Multiply the square of the time of flight by 16 for the range in _feet_
(the elevation being 45°).
14. What is meant by the penetration of projectiles?
The depth to which they are forced when fired into any resisting medium.
15. What depth do shot penetrate?
The penetration of balls of the same size, with different velocities or
charges, is nearly as the squares of the velocities; where the balls
are of different sizes the penetration will be proportionate to their
diameters multiplied by the density, and inversely as the tenacity of
the medium.
[Sidenote: 150]]
16. Mention the depth of penetration in case of the 24-pdr. siege-gun.
At 100 yards a 24-pdr. ball with a charge of one-third of its weight
will penetrate as follows:
Feet. Inches.
In earth of old parapets, 8 6
“ “ recently thrown up, 15 0
“ Oak wood, sound and hard, 4 6
“ Rubble stone masonry, 1 10
“ Brick, 3 0
17. What is the depth of penetration of field pieces?
Fired at the distance of 500 or 600 yards, the penetration will be
from 4½ to 6 feet in parapets recently constructed, and will traverse
walls of ordinary construction; but a 12-pounder is necessary to make a
breach in walls of good masonry and of 4 feet in thickness, and in this
case the position of the battery must be favorable, and the operation a
slow one.
18. In attacking a post, or fortified position, in what manner should
the fire from artillery be carried on?
Previous to an assault, the artillery ought to support the other
troops by a combined fire of guns, howitzers, and small mortars, so
that, if possible, the fire may be simultaneous, as such a diversity
of projectiles would tend to distract the defenders and prevent them
from extinguishing any fire among buildings, besides throwing them
into confusion at the moment of assault. In cases of surprise, when
immediate action is required, the above method cannot, of course, be
practicable.
19. When firing guns of different calibres at long ranges, what are the
probabilities of hitting the object?
As the squares of the diameters of their respective shot, when of equal
density, and fired with proportional charges.
[Sidenote: 151]]