position of its axis, it will be seen that the lower part of the bullet
re-establishes the air compressed, whilst the upper part finds itself in
the rarified air. That, consequently the lower parts of the cannelures
are submitted to the direct action of the air’s resistance, whilst their
upper parts totally escape this action. (Plate 21, fig. 2). The
resultant of the air’s resistance evidently tends to bring back the
point of the moving body, according to the trajectory; but as this
action is produced by the pressure of an elastic fluid, it results that
the point B, after having been an instant upon the trajectory, will fall
below, in virtue of the velocity acquired; but then the upper grooves
finding themselves acted on by the action of the air’s resistance, this
action, joined to its weight, will force the point of the projectile
upwards, which will descend to come up again, so that the projectile
will have throughout its flight a vertical swing, which is seen
distinctly enough in arrows.
~Union of Robins and Tamisier.~
Let us connect the suggestion of Robins, with the experiments of Captain
Tamisier, to cause the posterior end to act as a rudder to guide the
projectile in its true path, as undoubtedly during the descent of a
bullet there is a tendency for the centre of gravity to fall first, as
the ball of the shuttlecock. In the first Prussian balls, and in those
used in the Tige, the centre of gravity being nearer the base, the rear
end of these balls have a tendency to fall before the foremost, but this
is most undoubtedly counteracted by grooves, while it would be
impossible to fire an elongated projectile with its centre of gravity
backwards, with any accuracy out of a smooth-bored gun.
~Cannelures improved shooting.~
~Why none in English bullet.~
Captain Jervis says that these grooves have the effect of improving the
accuracy of firing when the bullets are not perfectly homogeneous, is
certain, but the British Committee on small arms justly considered that
owing to the careful way in which the bullets are made in England by
compression, these grooves might be dispensed with.
~Variety of forms.~
~Auxiliaries to expansion, various.~
Almost every conceivable form of projectile, internal and external, have
been made and experimented upon. Auxiliaries to expansion have been
used, made of metal, horn, wood, and leather, with plugs, screws, or
cups of divers shapes. Cannelures are used, of varying forms, depth and
number.
~Rotation from smooth bores.~
It has even been attempted to construct bullets upon the screw
principle, so that the projectile should receive spirality from the
action of the air upon its outer or inner surface, when fired out of a
smooth bore musket.
~General characteristics of modern rifles.~
The general characteristics of the European rifles, up to 1850, are a
very large calibre, a comparatively light short barrel, with a quick
twist, _i.e._, about one turn in three feet, sometimes using a patch,
and sometimes not, the bullet circular, and its front part flattened by
starting and ramming down.
~American alterations.~
It appears that the introduction of additional weight in the barrel,
reduction in the size of the calibre, the constant use of the patch, a
slower twist, generally one turn in 6ft., combined with (what is now
known to be a detriment) great length of barrel, are exclusively
American.
~Picket bullet.~
A round ended picket (plate 20, fig. 16), was occasionally used in some
parts of the States, until the invention of Mr. Allen Clarke, of the
flat ended picket, which allows a much greater charge of powder,
producing greater velocity, and consequently less variation in a side
wind.
~On the comparative merits of rifles.~
~Points in a perfect rifle.~
A rifle may perform first rate at short ranges, and fail entirely at
long, while a rifle which will fire well at extreme ranges can never
fail of good shooting at short. In fact certain calibres, &c., &c., &c.,
perform best at certain distances, and in the combinations of a perfect
rifle there are certain points to be attended to, or the weapon will be
deficient and inferior.
~Velocity.~
It is desirable to give a bullet as much velocity as it can safely be
started with, and the limit is the recoil of the gun, and the liability
of the bullets to be upset or destroyed, for as soon as this upsetting
takes place, the performance becomes inferior, and the circle of error
enlarged.
~Degree of twist.~
It is clear that a bullet projected with sufficient twist to keep it
steady in boisterous and windy weather, must of necessity have more
twist than is actually necessary in a still favourable time; hence a
rifle for general purposes, should always have too much twist rather
than too little.
~Weight of bullet.~
The weight of the bullet must be proportioned to the distance it is
intended to be projected with the greatest accuracy; for it is a law,
that with bodies of the same densities, small ones lose their momentum
sooner than large ones. It would be madness to use a bullet ninety to
the pound at nine hundred yards, merely because it performed first rate
at two hundred yards; or a forty to the pound at two hundred yards,
because it performed well at nine hundred yards. The reason is that a
forty to the pound cannot be projected with as much velocity at two
hundred yards, as the ninety to the pound can, because the ninety uses
more powder in proportion to the weight of the bullet than the forty
does. Again, the heavier bullet performs better than the lighter one at
nine hundred yards, simply because the momentum of the light ball is
nearly expended at so long a range as nine hundred yards, and its
rotatory motion is not enough to keep it in the true line of its flight,
whereas a heavy bullet, having from its weight more momentum, preserves
for a longer distance the twist and velocity with which it started.
~Calibre.~
As weight of projectile is a leading element in obtaining accuracy at
long ranges, and as the weight cannot be increased beyond a certain
limit in small arm ammunition, hence a small bore is an indispensable
requisite for a perfect rifle.
~Result of Mr. Whitworth’s experiments.~
In the foregoing brief summary of the most important properties which
should be possessed by a first class rifle, we have dealt in
generalities, but we shall now record the experience of Mr. Whitworth,
who has entered into the most minute details, and has pointed out the
harmony which should subsist between the twist, bore, &c., and the
projectile, in the combinations of a perfect rifle.
~Bore and weight limited.~
Premising, that when Mr. Whitworth was solicited by the late honored
Lord Hardinge to render the aid of his mechanical genius to the
improvement or perfecting a military weapon, he was restricted as to
length of barrel, viz., 3 feet 3-in., and weight of bullet, ·530 grains.
We shall now proceed and use Mr. Whitworth’s words.
~Consideration for curve.~
“Having noticed the form (hexagonal) of the interior which provides the
best rifling surfaces, the next thing to be considered is the proper
curve which rifled barrels ought to possess, in order to give the
projectile the necessary degree of rotation.”
~Hexagonal form admits of quick turn.~
“With the hexagonal barrel, I use much quicker turn and can fire
projectiles of any required length, as with the quickest that may be
desirable they do not ‘strip.’ I made a short barrel with one turn in
the inch (simply to try the effect of an extreme velocity of rotation)
and found that I could fire from it mechanically--fitting projectiles
made of an alloy of lead and tin, with a charge of 35 grains of powder
they penetrated through seven inches of elm planks.”
~Degree of spiral fixed.~
~Diameter of bore determined.~
After many experiments, in order to determine the diameter for the bore
and degree of spirality, Mr. Whitworth adds: “For an ordinary military
barrel, 39 inches long, I proposed a ·45-inch bore, with one turn in 20
inches, which is in my opinion the best for this length. The rotation is
sufficient with a bullet of the requisite specific gravity, for a range
of 2000 yards.” Under these conditions the projectiles on leaving the
gun would be about two and a half diameters of the bore in length. “The
gun responds to every increase of charge, by firing with lower
elevation, from the service charge of 70 grains up to 120 grains; this
latter charge is the largest that can be effectively consumed, and the
recoil then becomes more than the shoulder can conveniently bear with
the weight of the service musket.
~Advocates of slow turn.~
~Effects of quick turn.~
“The advocates of the slow turn of one in 6 feet 6 inches, consider that
a quick turn causes so much friction as to impede the progress of the
ball to an injurious and sometimes dangerous degree, and to produce loss
of elevation and range; but my experiments show the contrary to be the
case. The effect of too quick a turn, as to friction, is felt in the
greatest degree when the projectile has attained its highest velocity in
the barrel, that is at the muzzle, and is felt in the least degree when
the projectile is beginning to move, at the breech. The great strain put
upon a gun at the instant of explosion is due, not to the resistance of
friction, but to the _vis inertiæ_ of the projectile which has to be
overcome. In a long barrel, with an extremely quick turn, the resistance
offered to the progress of the projectile is very great at the muzzle,
and although moderate charges give good results, the rifle will not
respond to increased charges by giving a better elevation. If the barrel
be cut shorter, an increase of charge then lowers the elevation.”
~Objections to increasing spiral.~
“The use of an increasing or varying turn is obviously injurious, for
besides altering the shape of the bullet, it causes increased resistance
at the muzzle, the very place where relief is wanted.”
~Length and spiral increased.~
~Diameter decreased.~
~Trajectory lowered.~
“Finding that all difficulty arising from length of projectiles, is
overcome by giving sufficient rotation, and that any weight that may be
necessary can be obtained by adding to the length, I adopted for the
bullet of the service weight, an increased length, and a reduced
diameter, and obtained a comparatively low trajectory; less elevation is
required, and the path of the projectile lies more nearly in a straight
line, making it more likely to hit any object of moderate height within
range, and rendering mistakes in judging distances of less moment. The
time of flight being shortened, the projectile is very much less
deflected by the action of the wind.”
~Proper powder for expanding bullets.~
~Powder for hardened bullets.~
~Consequences of imperfect expansion.~
~Advantages of hexagonal form.~
“It is most important to observe that with all expanding bullets proper
powder must be employed. In many cases this kind of bullet has failed,
owing to the use of a slowly igniting powder, which is desirable for a
hard metal projectile, as it causes less strain upon the piece, but is
unsuitable with a soft metal expanding projectile, for which a quickly
igniting powder is absolutely requisite to insure a complete expansion,
which will fill the bore. Unless this is done the gases rush past the
bullet between it and the barrel, the latter becomes foul, the bullet is
distorted, and the shooting must be bad. If the projectiles used be made
of the same hexagonal shape externally as the bore of the barrel
internally, that is, with a mechanical fit, metals of all degrees of
hardness, from lead, or lead and tin, up to hardened steel may be
employed, and slowly igniting powder, like that of the service may be
employed.”
~Mr. Whitworth’s claims.~
Mr. Whitworth does not lay claim to any originality as inventor of the
polygonal system, but merely brings it forward, as the most certain mode
of securing spiral motion, but he deserves to be honored by all
Riflemen, as having established the degree of spirality, the diameter of
bore, to ensure the best results from a given weight of lead, and length
of barrel.
CONCLUSION.
In achieving the important position obtained by the rifle in the present
day, it has nevertheless effected no more than was predicted of it by
Leutman, the Academician of St. Petersburg, in 1728, by Euler, Borda,
and Gassendi, and by our eminent but hitherto forgotten countryman
Robins, who in 1747, urgently called the attention of the Government and
the public to the importance of this description of fire-arm as a
military weapon.
In the War of American Independence, the rifle, there long established
as the national arm for the chase, exhibited its superiority as a _war_
arm also, in so sensible a manner, that we were constrained to oppose to
the American hunters the subsidised Riflemen of Hesse, Hanover, and
Denmark.
~Robins’ prophecy.~
We shall close by quoting the last words in “Robins’ Tracts of Gunnery.”
“Whatever State shall thoroughly comprehend the nature and advantages of
rifled barrel pieces, and having facilitated and completed their
construction, shall introduce into their armies their _general_ use with
a _dexterity_ in the _management_ of them; they will by this means
acquire a superiority, which will almost equal anything that has been
done at any time by the particular excellence of any one kind of arms;
and will perhaps fall but little short of the wonderful effects which
histories relate to have been formerly produced by the first inventors
of fire-arms.”
NOTE.--The preceding articles on the Rifle, Rifling, and Rifle
Projectiles are mainly compiled from: “New Principles of Gunnery, by
Robins,” “Scloppetaria,” “Remarks on National Defence, by Col. the
Hon. A. Gordon,” “Dean’s Manual of Fire Arms,” “Rifle Ammunition, by
Capt. A. Hawes,” “Rifles and Rifle Practice, by C. M. Wilcox,” “Papers
on Mechanical Subjects, by Whitworth,” “The Rifle Musket, by Capt.
Jarvis, Royal Artillery,” “Des Armes Rayees, by H. Mangeot,” “Cours
Elementaire sur les Armes Portatives, by F. Gillion,” and “Cours sur
les Armes a feu Portatives, by L. Panot.”
THEORETICAL PRINCIPLES.
DEFINITIONS.
~Matter.~
Matter,--everything which has weight.
~Body.~
Body,--a portion of matter limited in every direction.
~Mass.~
Mass,--the quantity of matter in any body.
~Particle.~
Particle,--or material point, is a body of evanescent magnitude, and
bodies of finite magnitude are said to be made up of an indefinite
number of particles, or material points.
~Inertia.~
Inertia,--passiveness or inactivity.
~Attraction.~
Attraction,--a fundamental law of nature, that every particle of matter
has a tendency to be attracted towards another particle.
~Density.~
Density,--is in proportion to the closeness of the particles to each
other.
~Volume.~
Volume,--the space bounded by the exterior surface of a body, is its
apparent volume or size.
~Elasticity.~
Elasticity,--a body that yields to pressure, and recovers its figure
again; hence air and gasses are elastic bodies; lead a non-elastic body.
~Motion.~
Motion,--is the changing of place, or the opposite to a state of rest.
~Velocity.~
Velocity,--is the rate of motion; there are four rates of motion, viz.,
Uniform, Variable, Accelerated, and Retarded.
~1st. Uniform.~
1st. Uniform,--when a particle traverses equal distances, in any equal
successive portion of time.
~2nd. Variable.~
2nd. Variable,--when the spaces passed over in equal times, are unequal.
~3rd. Accelerated.~
3rd. Accelerated,--when the distances traversed in equal times are
successively greater and greater.
~4th. Retarded.~
4th. Retarded,--when the distances traversed in equal times are
successively less and less.
Acceleration or Retardation, may also be equal or unequal, that is
uniform or variable.
~Friction.~
Friction,--arises from the irregularities of the surfaces which act upon
one another.
~Force.~
Force,--any cause which produces, or tends to produce a change in the
state of rest, or of motion of a particle of matter.
~Measure of force.~
Forces are measured by comparison with weights. Thus any forces which
will bend a spring into the same positions as weights of 1lb., 2lbs.,
3lbs., &c., are called respectively forces of 1lb., 2lbs., 3lbs., &c.,
&c.
~Momentum.~
Momentum,--or quantity of motion. If a body moving at first with a
certain velocity is afterwards observed to move with double or triple
this velocity, the quantity of motion of the body is conceived to be
doubled or tripled, hence the momentum of a body, depends upon its
velocity, as the quantity of motion of a body is the product of the
velocity by the mass or weight.
~Laws of motion.~
The elementary principles upon which are based all our reasonings
respecting the motions of bodies, are called the “Laws of Motion,” and
as arranged by Sir Isaac Newton, are three in number.
~1st Law.~
1st. A particle at rest will continue for ever at rest, and a particle
in motion will continue in motion uniformly forward in a straight line,
until it be acted upon by some extraneous force.
~2nd Law.~
2nd. When any force acts upon a body in motion, the change of motion
which it produces is proportional to the force impressed, and in the
direction of that force.
~3rd Law.~
3rd. Action and reaction are equal, and in contrary directions. In all
cases the quantity of motion gained by one body is always equal to that
lost by the other in the same direction. Thus, if a ball in motion,
strikes another at rest, the motion communicated to the latter will be
taken from the former, and the velocity of the former be proportionately
diminished.
~Centre of Gravity.~
Centre of Gravity,--is that point at which the whole weight of the body
may be considered to act, and about which consequently, the body, when
subjected to the force of gravity only, will balance in all positions.
~Specific Gravity.~
Specific Gravity,--the weight belonging to an equal bulk of every
different substance, and is estimated by the quantities of matter when
the bulks are the same; or in other words, it is the density that
constitutes the specific gravity. It is agreed to make pure rain-water
the standard, to which they refer the comparative weights of all other
bodies. Lead is about eleven times the weight of the same bulk of water.
~Initial Velocity.~
Initial Velocity is the velocity which a bullet possesses on leaving the
muzzle of a gun; and in the speaking of the velocity of bullets fired
from the musket now used, you understand 1200 feet per second, for the
Initial Velocity.
~Angular Velocity.~
Angular Velocity is the velocity with which the circular arc is
described; and depends upon the perpendicular distance of the point from
the axis of rotation.
~Terminal Velocity.~
Terminal Velocity: if a cannon ball were to be let fall from a very
great height, it would by the law of gravity, descend with accelerated
motion towards the earth, but as the resistance of the air increases as
the squares of velocities, a point would be reached when the resistance
would be equal to the force of gravity, from whence it would fall to the
earth in uniform motion.
~Eccentric Body.~
An Eccentric Body, is one whose centre of figure does not correspond
with the centre of gravity.
MOTION OF A PROJECTILE.
~Modified by Gravity and air.~
If no force were acting upon the projectile, except the explosive force
of gunpowder, it would by the first law of motion, move on for ever in
the line in which it was discharged; this motion is modified by the
action of two forces, viz., gravity and the resistance of the air.
As the early cannons were of the rudest construction, and were used only
to force open barriers, or to be employed against troops at a very short
range, it was a matter of secondary consideration what course the bullet
took, indeed it was generally believed, that it flew for some distance
in a straight line, and then dropped suddenly. Acting upon this opinion
we find that most of the early cannon had a large metal ring at the
muzzle, so as to render it the same size as at the breech, and with such
as were not of this construction they made use of a wooden foresight
which tied on to the muzzle, so as to make the line of sight parallel to
the axis, by which they conceived that they might aim more directly at
the object which the bullet was designed to hit.
~Leonardo da Vinci, 1452.~
The first author who wrote professedly on the flight of a cannon shot
was a celebrated Italian Mathematician, named Leonardo da Vinci, who
explains his manner of studying phenomena, in order to arrive at safe
conclusions, thus: “I will treat of the subject, but first of all I will
make some experiments, because my intention is to quote experience, and
then to show why bodies are found to act in a certain manner;” and
taking as his motto, “Science belongs to the Captain, practice to the
Soldier,” he boldly asks: “If a bombard throws various distances with
various elevations, I ask in what part of its range will be the greatest
angle of elevation?” The sole answer is a small drawing of three curves,
(plate 20, fig. 3.), the greatest range being the curve about midway
between the perpendicular and the horizontal. Yet this small drawing is
very remarkable when we come to examine it. In the first place, we see
that he recognises the fact that the trajectory is a curve throughout
its length; secondly, that a shot fired perpendicularly will not fall
again on the spot whence it was fired. Simple as they may seem, these
two propositions recognise the force of gravity, resistance of the air,
and the rotary motion of the earth.
~Tartaglia, 1537.~
The next author who wrote on the flight of cannon shot was another
celebrated Italian Mathematician, named Tartaglia. In the year 1537, and
afterwards in 1546, he published several works relating to the theory of
those motions, and although the then imperfect state of mechanics
furnished him with very fallacious principles to proceed on, yet he was
not altogether unsuccessful in his enquiries, for he determined
(contrary to the opinion of practitioners) that no part of the track of
a bullet was in a straight line, although he considered that the
curvature in some cases was so little, as not to be attended to,
comparing it to the surface of the sea, which, although it appears to be
a plain, when practically considered, is yet undoubtedly incurvated
round the centre of the earth. It was only by an accident he nearly
stumbled upon one truth in the theory of projectiles, when he stated
that the greatest range obtained by equal forces is at 45°. Calculating
that at the angle 0° the trajectory was null, that by raising the
trajectory, the range increased up to a certain point, afterwards
diminished, and finally became null again when the projective force
acted perpendicularly, he concluded that the greatest range must be a
medium between these two points, and consequently at 45°.
Others thought that a shot, on leaving the muzzle, described a straight
line; that after a certain period its motion grew slower, and then that
it described a curve, caused by the forces of projection and gravity;
finally, that it fell perpendicularly. Tartaglia seems to have
originated the notion that the part of the curve which joined the
oblique line to the perpendicular, was the arc of a circle tangent to
one and the other.
~Galileo, 1638.~
In the year 1638, Galileo, also an Italian, printed his dialogues, in
which he was the first to describe the real effect of gravity on falling
bodies; on these principles he determined, that the flight of a cannon
shot, or of any other projectile, would be in the curve of a parabola,
unless it was deviated from this track by the resistance of the air. A
parabola is a figure formed by cutting a cone, with a plain parallel to
the side of the cone.
GRAVITY.
~Bullet as influenced by powder and gravity only.~
We will now proceed to consider the course of a bullet, as affected by
_two_ forces only, viz., 1st. The velocity communicated to it by the
explosion of the powder; and 2nd. By the force of Gravity.
The attraction of the earth acts on all bodies in proportion to their
quantities of matter.
~If no air, all bodies would fall in same time.~
~Gold and dry leaf in same time.~