Circular grooving is composed of segments of circles, leaving no sharp
edges on the bullet, and is no doubt a very good form.
~Gaining twist.~
~Cause of canting.~
An American gentleman named Chapman, who has written a very clever book
upon the rifle, is a strong advocate for the “gaining twist,” which form
prevails generally in American rifles. He states, “In a rifled barrel,
it is obvious that a bullet instantaneously started from a state of
rest, with a velocity of 5,000ft. a second, must exert at the moment of
starting, a tendency to move along the bore in a straight line. However,
meeting with the resistance that the lands employ to keep it to the
twist, it communicates to the rifle itself a certain amount of motion in
the direction of the twist of the creases, and this as the angle of the
twist increases, combined with the size of the calibre, and the weight
of the ball.”
~Remedy for canting.~
“If the angle of the twist at the breech end can be reduced, the bullet
at the same time leaving the muzzle with sufficient spin to last
throughout its flight, it is certain we shall have less twisting of the
rifle in the marksman’s hands, less friction of the bullet against the
lands, less tendency for the bullet to upset, (or be destroyed,) and
consequently, from obtaining a higher velocity, (because enabled to use
a greater quantity of powder,) less time for the action of regular or
irregular currents of air.”
~Uniform spiral by American Government.~
After careful experiments by the American Government, preparatory to the
establishing the model for their Military Rifle, it was decided that the
turn for the grooves should be uniform; and that those with an
increasing twist did not give any superiority of accuracy. The “gaining
twist,” although adopted by Mr. Lancaster, is opposed by Mr. Whitworth,
and all other Rifle manufacturers, and our increased experience does not
prove it to possess any advantages over uniform spirality. Theory would
indicate that it must occasion increased friction.
~Decreasing spiral.~
Mr. Greener advocates decreasing spirality. It is to be hoped he is the
only advocate for so seemingly absurd an idea. To give a certain measure
of spiral turn at the breech, to be withdrawn gradually as the bullet
reaches the muzzle, is simply ridiculous, and which, with other conceits
previously referred to, it is to be hoped are no more to be repeated.
~Polygonal rifling.~
By the desire of our first Patron, the late Lord Hardinge, Mr. Whitworth
was induced to turn his mechanical genius to the Soldier’s Gun, which
resulted in his adopting the polygonal form of bore. His barrel is
hexagonal, and thus, instead of consisting of non-effective lands, and
partly of grooves, consists entirely of effective rifling surfaces. The
angular corners of the hexagon are always rounded. Supposing a bullet of
a cylindrical shape to be fired, when it begins to expand it is driven
into the recesses of the hexagon. It thus adapts itself to the curves of
the spiral, and the inclined sides of the hexagon offering no direct
resistance, expansion is easily effected.
~Westley Richards octagonal.~
Mr. Westley Richards has followed Mr. Whitworth, by using a polygonal
bore, having applied his highly meritorious system of breech-loading to
a barrel upon the Whitworth principle, of an octagonal form.
~Eliptic rifling.~
~By Captain Berner, 1835.~
~By Mr. Lancaster.~
The cardinal feature of this structure is, that the bore of the barrel
is smooth, and instead of being circular, is cut into the form of an
ellipse, i.e., it has a major and minor axis. Upon being expanded by the
force of the powder, the bullet is forced into the greater axis of the
ellipse, which performs the office of the grooves, rifling the
projectile, and imparting to it the spiral or normal movement round its
own axis. In 1835 a Captain Berner submitted his elliptical bore musket
to the inspection and trial of the Royal Hanoverian Commission,
appointed for that purpose, and which gave results so satisfactory, that
it was considered admirably adapted for the Jäger and Light Infantry
Battalions. This principle has been patented by Mr. Lancaster, and the
advantages of this form have been previously adverted to.
~Odd number of grooves.~
It is supposed by some persons that if the number of grooves be even, so
that they will be opposite to one another, the bullet would then require
more force to enlarge it, so as to fill them properly. If the number be
unequal, the lands will be opposite to the grooves, and the lead, in
forcing, spreading on all sides, will encounter a land opposite to each
groove, which will in some measure repel it, and render its introduction
into the opposite groove more complete.
This ingenious theory is set at nought by Whitworth, Jacobs, Lancaster,
W. Richards, &c., &c., who all recommended an even number of grooves,
while the Government arms have an odd number.
~Drift or cant.~
If the grooves twist or turn over from left to right, the balls will be
carried to the right; and if from right to left, they will group to the
left; and this result will be great in proportion to the degree of
spirality. The causes of Drift or “Derivation” will be treated of
hereafter. We know from observation that the majority of balls strike to
the right of the mark. The recoil and _pulling_ the trigger throw back
the right shoulder, which tend to increase the “derivation” to the
right. If the twist were, then, from _right_ to _left_, the drift, error
from _pulling_, and from recoil, would tend to neutralize each other;
the twist of the grooves should therefore be from right to left, instead
of the present universal practice of from _left_ to right.
~On length of barrel.~
~Favors expansion.~
~Assists aiming, firing two deep: when using bayonet.~
The barrel of a gun may be looked upon as a machine in which force is
generated for the propulsion of the bullet. It is well known that the
continued action of a lesser force, will produce a much greater effect,
than a greater amount of power applied suddenly; hence mild gunpowder is
more suitable for rifle shooting than strong, or that which evolves the
whole of its gas instantaneously. Time is necessary for the entire
combustion of a charge of gunpowder, consequently more mild gunpowder
can be fired out of a long, than out of a short barrel, as if fired out
of a short barrel, some of the grains might be ejected unconsumed. All
extra length, after the last volume of gas is evolved, can only be
injurious, by causing loss of velocity from friction. A billiard ball
would travel none the further nor straighter, were it to be propelled
through a hollow tube, neither would a barrel to a cross bow aid in
killing rooks. A barrel favours expansion of the bullet, which is
produced by the force of the generated gas, opposed by the column of air
in the hollow tube and by the motion of the projectile. Facility in
aiming is promoted by the sights being distant from each other. In a
military arm a certain length is necessary in order to fire when two
deep in the ranks, and length is also advantageous, should the rifle be
used as a pike.
~Advantages of short rifle.~
~Disadvantages of short rifles.~
The short rifle can be held steadier when standing, by a weak man, and
during wind, it is handy when passing through a wood or thicket, and a
very short man has more command of his gun when loading; but with the
sword bayonet, it is heavier than the long Enfield and bayonet; while
the sword is very inconvenient when running, firing kneeling, or lying
down.
~Thickness of barrel.~
Great substance was at one time considered necessary for accurate
firing, it being supposed necessary to prevent vibrations in the barrel;
this is true within certain limits, and the heavier the charge, the
heavier the metal ought to be, especially at the breech, but diminishing
the thickness, has been proved in no wise to lessen the accuracy. A
heavy barrel also lessens recoil, but it would be folly to carry more
weight than would neutralize the recoil which could be produced by a
greater charge of powder than could be consumed in a given length of
barrel.
~Size of bore.~
The two grand requirements of a soldier’s gun are, celerity of loading,
combined with accuracy at long ranges; and the distance at which he
should have the power of firing, should be limited by the strength of
his eye. The weight of the projectile being fixed (·530 grs.), good
shooting at extreme distances can only be obtained by reducing the
diameter of the bore, which, lessening the frontage of the bullet,
causes it to experience less resistance from the air; it therefore
retains a higher degree of velocity than a larger bullet of the same
form and weight, and therefore travels further and faster. Gravity has
less time to act upon it, in a given distance, and therefore it can be
fired at a lower angle, or has what we call a lower trajectory, and its
accuracy is increased in direct proportion to the lowness of its flight,
all other things being equal.
~Best form of rifling still undetermined.~
While the best form, &c., &c., for rifles is not yet determined, there
are many points upon which the generality of persons seem more agreed,
viz., reduction of bore to about ¹⁄₂-in. in diameter, fewer grooves,
shorter barrel, and with increased spirality; at least, one may safely
say that ideas seem to travel in this direction.
ON RIFLE PROJECTILES.
~Projectiles used in early guns.~
~Elliptical iron bullets 1729.~
We have learned that out of early Artillery were fired bolts, darts,
bombs, stones and (more recently) iron shot. From the harquebus and
musket: arrows, darts, quarrels, sprites, iron, and lastly leaden
spherical balls. Some assert that the idea of lengthened eliptical
bullets was enunciated so far back as 1729, and that good results
followed their employment, but it is doubtful whether such really did
take place.
~Leutman.~
Leutman, in his “History of St. Petersburgh,” says that “it is very
profitable to fire elliptical balls out of rifled arms, particularly
when they are made to enter by force.”
~Robins 1742.~
Robins, in 1742, recommended the use of projectiles of an egg like form,
(see plate 20, fig. 12), they were to be fired with the heavy end in
front, to keep the centre of gravity forward.
~Beaufoy 1812.~
Colonel Beaufoy, in a work called “Scloppetaria,” 1812, remarks that
several experiments have been tried with egg-shaped bullets, recommended
by Robins. It was found, however, that these bullets were subject to
such occasional random ranges, as completely baffled the judgment of the
shooters to counteract their irregularity. Their deviations to windward
most likely arose from the effect of the wind on the after part, which,
as being the lightest of the two, was driven more to leeward, and
consequently acted as a rudder to throw the foremost end up to the wind.
~Turpin 1770.~
In 1770 Messrs. Turpin tried elongated bullets, at La Fiere, and at
Metz.
~Rifled guns &c., 1776.~
We are informed, in the Annual Register for 1776, and also in the Scots
Magazine for the same year, that rifled Ordnance were experimented with
at Languard Fort, &c., &c., in 1774. Dr. Lind, one of the inventors,
states that to remedy the deflection of shot, “One way is to use bullets
that are not round but oblong. But in our common guns that are not
rifled, I know no way to prevent deflection, except you choose to shoot
with a rifled bullet.”
~Elongated projectiles 1789.~
~1800 and 1815.~
Elongated Projectiles were tried in the years 2, 6, and 9 of the
Revolution, by Mons. Guitton de Moreau. They were proposed by Mons.
Bodeau. In 1800 and 1815 the Prussians tried ellipsodical bullets.
Colonel Miller, Colonel Carron, Captain Blois, and others, also
experimented with the cylindro-conical form.
~Captain Norton 1824.~
Captain Norton (late 34th Regt.), the original inventor of the
application of the percussion principle to shells for small arms, in
1824, completed an elongated rifle shot and shell, the former precisely
of the form of the Minié bullet, with projections to fit the grooves of
the barrel.
~Mr. Greener 1836.~
Mr. Greener, in 1836, presented an expanding bullet to the Government
for experiment, (plate 20, fig. 13). It is oval, with a flat end, and
with a perforation extending nearly through. A taper plug, with a head
like a round-topped button, is also cast of a composition of lead and
zinc. The end of the plug being slightly inserted in the perforation,
the ball is inserted either end foremost. When the explosion takes
place, the plug is driven home into the lead, expanding the outer
surface, and thus either filling up the grooves of the rifle, or
destroying the windage of the musket. The result was favourable beyond
calculation. Of about 120 shots by way of experiment, a man was able to
load three times to one of the old musket, and accuracy of range at 350
yards was as three to one.
~Mr Greener’s invention rejected.~
Mr. Greener’s invention was rejected, and the only notice he received
from the Board was, it being “a compound,” rendered it objectionable!!!
~Mr. Greener rewarded.~
The following extract appears in the Estimates of Army Service for
1857-8. “To William Greener, for the first Public Suggestion of the
principle of expansion, commonly called the Minié principle for bullets
in 1836, £1,000.”
~Wilkinson 1837.~
~Cork plug 1851.~
Many experiments were made by Mr. Wilkinson in 1837, with balls
precisely similar in shape to the Minié, with a conical hole in them,
using a wooden plug; and in 1851 experiments were tried at Woolwich with
a soft elastic cork, fitting the aperture in the projectile very
closely, the compression of which it was conceived would sufficiently
expand the cylindrical part, and make it fit the grooves, &c. In some
instances it succeeded perfectly, but in many the cork was driven
through the lead.
~Gen. Jacobs.~
~Form of leaden bullet destroyed.~
~Zinc point to bullets.~
Major-General Jacobs for many years carried on a series of experiments
with rifles, and in 1846 submitted a military rifle, with an elongated
projectile, for experiments, to the Government at home, and also to that
in India. It did not meet with approval in England, and the Company cut
the matter short by stating, that what was good enough for the Royal
Army was good enough for theirs. There is nothing peculiar in General
Jacob’s rifle. He recommends an elongated projectile (plate 20, fig. 14)
solid at the base, cast with four raised flanges to fit into the
grooves. General Jacobs states, that the desired initial velocity could
not be produced with a projectile made entirely of lead, as a slight
increase of charge had the effect of destroying the form of the
projectile. He also states that the limit of the powers of leaden balls
having been attained, it became necessary to find a method of
constructing rifle balls, so that the fore part should be capable of
sustaining the pressure of large charges of fired gunpowder, without
change of form, and retain that shape best adapted for overcoming the
resistance of the air, on which all accurate distant practice depends;
and at the same time having the part of the ball next the powder
sufficiently soft and yielding to spread out under its pressure, so as
to fill the barrel and grooves perfectly air tight. And he professes to
have solved the problem, by having the fore part of the bullet cast of
zinc, in a separate mould.
~Expansion by hollow bore.~
Captain Delvigne, who had been experimenting since 1828, proposed the
adoption of lengthened bullets, consisting of a cylinder terminated by a
cone, which was subsequently replaced by an ogive. He obtained a patent
dated 21st June, 1841, “For having hollowed out the base of my
cylindro-conical bullet, to obtain its expansion by the effect of the
gases produced through the ignition of the powder.”
~Hollow in case to throw centre of gravity forward.~
The main object of Captain Delvigne in hollowing the base was, to throw
the centre of gravity forward; but a Captain Blois, in France, had
previously tried this important suggestion. Captain Delvigne states, if
the hollow is too deep, the expansion is too great, and the consequent
friction enormous; or the gas may pass through the bullet, and leave a
hollow cylinder of lead within the barrel. Sometimes the gas will
traverse the sides of the bullet, and consequently the projectile is
deprived of a proportionate amount of velocity; if too small, the
expansion does not take place.
~Capt. Minié iron cup.~
Captain Minié, an instructor of the School at Vincennes, merely fitted
into this hollow an iron cup, hoping to prevent the gas forcing its way
through the bullet, and that the iron pressing upon the lead should
increase the expansion. (Plate 20, fig. 7).
~Groove suppressed.~
A perfect bullet was now supposed to have been discovered, of a
cylindro-ogival form, (no part was a true cylinder), having a groove
originally intended to fasten on a greased patch, and in some cases the
cartridge, but the patch being dispensed with, and the cartridge
reversed, the groove, supposed to be useless, was suppressed.
~Results.~
People were then surprised to find that firing lost much of its
accuracy, and the groove was replaced; when it was observed that any
variation in its shape and in its position, materially affected the
practice. Not only variations in the grooves caused great alteration in
the accuracy of fire, but any modification bearing on the trunk in rear,
or on the fore-ogive, altered the conditions of the firing, so that the
groove became lost in the midst of so many other principles, the
functions of which were so much unknown. These theoretical
considerations served, however, as a point of departure for further
investigations.
~Tamisier lengthened bullets.~
Captain Tamisier had not ceased for several years, concentrating his
attention on the subject. He varied the length of the cylindrical part
and the angle of the cone, and tried experiments with bullets of 5-in.
in length, and obtained considerable range, and great accuracy with
them; the recoil however was excessive, and to use such bullets heavier
arms, a smaller bore, and other modifications would be necessary.
~Centre of gravity formed by blunting tips.~
He endeavoured to carry the centre of gravity to the furthest possible
point forward, (which Robins suggested 100 years before), but to effect
this he was compelled to flatten the fore end of the bullet, which had
the disadvantage of increasing the resistance of the air to the movement
of projection.
~Path rectified by resistance in rear.~
~Many cannelures.~
He was then led to another plan for rectifying the path of the bullet
through each instant of projection, and which was by creating at the
posterior end, resistances, which should act in case the axis of the
bullet did not coincide with the direction of motion, and this was
carried out by cutting upon the cylindrical part, instead of one, as
many circular grooves of ·28 in depth, as that cylindrical, or rather,
slightly conical, part could contain. An increased precision in firing
was the immediate result. (Plate 20, fig 15.)
~Shape of cannelures.~
Feeling his way most carefully, Captain Tamisier then made a great
number of experiments in this direction, and perceived that it was
important to render the posterior surface of the grooves as sharp as
possible, so as to augment the action of the air; for these grooves lose
their shape, owing to the lead, from its malleable nature, yielding
under the strokes of the ramrod.
~Elongated Projectiles, whose Centres of Gravity do not correspond
with Centre of Figure.~
~Action of the air.~
Elongated projectiles, whose centres of gravity do not exactly coincide
with the centre of figure, when they do not turn over, tend to preserve
their axis in the primary direction which was imparted to them, in the
same manner as an imperfectly feathered arrow flying with little
velocity, the point of the moving body being constantly above the
trajectory, and its axis making a certain angle (plate 21, fig 1) with
the target to the curve. Therefore the part A.B. of the bullet being
exposed to the direct action of the air’s resistance, the atmospherical
fluid is compressed on the surface A.B., and rarified upon that of A.C.
Hence it will be perceived that the compressed fluid supports the moving
body, and prevents its descending as rapidly as would a spherical
bullet, which is constructed to meet the same direct resistance from the
air. This trajectory will therefore be more elongated than that of the
spherical bullet in question.
~Remedied by the grooves.~
~Cause of deviation.~
~Remedy.~
But the resistance of the air, acting upon the groove of the projectile,
produces, on the lower part of this groove, an action which tends to
bring back its point upon the trajectory, yet with so little force, that
often, in its descent, the projectile turns over, and moves breadthways
at ranges of 1000 and 1200 yards. The lower side of the projectile,
therefore, moving in the compressed air, and the upper in the rarified
air, deviation must ensue, for, as the upper part of the bullet moves
from left to right, the bottom must move from right to left. But the
lower resistance to the motion of rotation being produced by the
friction of the compressed air, is greater than the upper resistance,
which depends on the friction of the rarified air. By combining these
two resistances, there results a single force, acting from left to
right, which produces what Captain Tamisier termed “derivation,” and it
was to overcome this derivation that this officer proposed the circular
grooves to the bullet, which he considered would act, like the feathers
of the arrow, to maintain the moving body in its trajectory.
~How to obtain knowledge of the bullet’s rotation.~
~By the arrow.~
~Use of feathers on arrows.~
If, however, we would wish to obtain some idea of the rotatory motion of
a bullet in its path through the air, let us consider the action of the
arrow, and see how it is constructed, so that the resistance of the air
should not act in an unfavourable manner. First, nearly all its weight
is concentrated at the point, so that its centre of gravity is close to
it. At the opposite end feathers are placed, the heaviest of which does
not affect the centre of gravity, but gives rise to an amount of
resistance in rear of the projectile, and which prevents its ever taking
a motion of rotation perpendicular to its longer axis, and keeps it in
the direction of its projection. This difficulty which the arrow finds
in changing its direction must concur in preventing its descending so
rapidly as it would do were it only to obey the law of gravity, and must
therefore render its trajectory more uniform.
~Similar effects on bullet with grooves.~
Let us, however, now come back to the grooves of Mons. Tamisier, and we
shall find that they concur in giving to the bullet the two actions of
the resistance of the air, which we have demonstrated with respect to
the arrow.
~Effect of grooves.~