ON RIFLING.
It has been stated that amongst the different gun makers who assembled at Woolwich, for the carrying on of experiments in 1851, no two agreed upon any one thing; and in 1860, it may still be averred, with almost equal truth, and that it yet remains an unsettled question as to the form, width, depth, number or degree of spirality of the grooves, as also the harmony which should subsist between the grooves, diameter of bore, the form and weight of projectile, and the quality and quantity of charge.
Description of Rifles.
Robins, in 1742, says, “rifles though well known on the continent, being but little used in England, it is necessary to give a short description of their make. The rifle has its cylinder cut with a number of spiral channels, so that it is in reality a female screw, varying from the fabric of common screws, only in this, that its threads or rifles are less deflected and approach more to a straight line.” Advantages of a rifle.The advantage of a rifle (with a round bullet), is that the axis of rotation not being in any accidental position, as in a smooth bore, but coincident with the line of its flight, it follows that the resistance on the fore part of the bullet is equally distributed round the centre of gravity, and acts with an equal force on every side of the line of direction, and also should the resistance be greater on one side of the bullet than the other from irregularities on its surface, as this part continually shifts its position round the line in which it is proceeding, the deflections which this irregularity would occasion are neutralized. With an elongated projectile rifling also prevents it from rotating round its shorter axis.
Rifling invented in Germany.
It is to the artizans of Germany, that the rifle owes its origin, as at the close of the fifteenth century barrels with straight grooves were used by the citizens of Leipsic, at target practice, Rifles used 1498.in 1498, and the invention of grooving or rifling fire-arms is generally supposed to be the result more of accident than theory. In Dean’s Manual of fire-arms, it is stated that, “the idea of grooving arms in the direction of the axis of the barrel to receive the residium of the powder, and thereby, not only facilitate the loading, but increase both the bite or forcing of the ball, by impressing upon it the grooves, and thus maintain it during its passage through the barrel in a direction more in harmony with the line of fire, was doubtless a conception based upon no previous theory or practice now to be traced, but was formed in that suggestiveness which in the individual founds for itself a theory based upon the likelihood of possible result. Straight grooves.Upon trial also of the straight grooves a greater precision for short distances would have been observed than with the smooth bore.” This must of itself therefore have led to the establishment of a certain grade of theory which it was endeavoured to amplify by various means, such as increasing the number of grooves, then of changing the inclination of grooves from the straight line to the spiral.
To deem that the practised crack “shots and armourers of a time when target practice was the constant recreation of the citizen, and his pride to excel in, were so brainless as to conceive no theory, unelaborated though it may have been, and that all their even now admired efforts in Germany, were the products of mere accident, is therefore scarcely a rational supposition.”
Spiral grooves, by Koster, of Nuremberg in 1522.
It is stated that Koster, of Nuremburg, in 1522, first suggested giving a spiral form to the grooves, and experience proved that much greater accuracy of shooting was the result.
Damer of Nuremberg, 1552.
In 1552, Damer, of Nuremburg, made some great improvements in rifles, but we are not aware of their precise nature.
Koster of Nuremberg, 1620.
Koster, of Nuremburg, who died 1630, by some authorities is said to have discovered that straight grooves did not fulfil the intentions of their inventor, and to have been the first who suggested spiral grooves in 1620.
Robins first explained action of grooves.
The important stage next arrived at was the scientific explanation of the true value of spiral grooves. The honor of this entirely belongs to our countryman, Benjamin Robins, who in his Principles of Gunnery, gives a complete and satisfactory explanation of the action of the grooves in determining the flight of the bullet. Robins structure of rifles.Robins states that “the degree of spirality, the number of threads, the depth the channel are cut down to, are not regulated according to any invariable rule, but differ according to the country where the work is performed, and the caprice of the artificer. Modes of loading.The most usual mode of charging rifles is by forcing the ball with a strong rammer and mallet. But in some parts of Germany and Switzerland, an improvement is made by cutting a piece of very thin leather or fustian in a circular shape, somewhat larger than the bore, which being greased on one side is laid upon the muzzle with its greasy part downwards, and the bullet being placed upon it, is then forced down the barrel with it. When this is practised the rifles are generally shallow, and the bullet ought not to be too large.
Early rifles, breech-loaders.
As both these methods of charging rifles take up a good deal of time; the rifled barrels which have been made in England, (for I remember not to have seen it in any foreign piece,) are contrived to be charged at the breech, where the piece is made larger, and the powder and bullet are put in through an opening in the side of the barrel, which, when the piece is loaded is fitted up with a screw. And perhaps somewhat of this kind, though not in the manner now practised, would be of all others the most perfect method for the construction of these sorts of barrels.”
ON THE NUMBER, FORM &c., &c., &c., OF THE GROOVES.
Number of grooves.
Almost every description of twist, number, &c., &c., of grooves have been tried, according to the individual tastes and theories of the manufacturers. It is absolutely necessary to have two grooves, as a single one would give a wrong direction. Rifles have been made with, from two to one hundred and thirty three grooves, and in the majority of cases, an odd seems to have been preferred to an even number. In Dean’s Manual it is stated, Degree of spirality.that “in the numerous collections of arms that have at various times come under our personal notice, some were rifled with straight, but the majority with grooves in a spiral line, sometimes with a half, sometimes a three quarter, and seldom more than a whole turn in a length of two, two and a half and three feet; deviations based upon no principle transmitted to us, but requiring nevertheless a decided research for principles upon which to establish a theory; we have also met with every one of those configurations of the spiral and form of groove, &c., &c., which have been arrogated as modern conceits and discoveries.”
Spirality.
Some rifles have sharp muzzle twist decreasing to the breech;—sharp breech twist decreasing to the muzzle; an increase of twist in the middle of the barrel decreasing at both extremities.
Modification in France. 1740.
In France a modification of the Carabine took place in 1740;—the grooves were made to begin at eight inches from the muzzle, the unrifled part being of the same calibre as the bottom of the grooves, so that the bullet might pass easily; thus also facilitating the loading of the weapon.
Rifled only at muzzle.
There is an old rifle in the United Service Institution, and also a barrel brought from Lucknow, (in the Model Room of the School of Musketry,) grooved only for about one foot from the muzzle, the remainder of the barrels are smooth bored.
Degree of spirality.
The degree of spirality is found to vary from a whole turn in 1 foot 5-in., to a whole turn in 11 feet.
Depth of spiral.
The depth of grooves vary from ·005 of an inch, to about ·125; and some rifles have been made with an alternate deep and shallow groove.
Form of grooves.
Grooves have been made round, circular, triangular, rectangular, and indefinite, alternate round and angular, elliptical, polygonal; and some cut deep only on one side.
Proportion of groove to land.
Some gun makers are of opinion that there should be a greater proportion of groove or furrow than of land or plain surface, because they say the ball is thus more firmly held, while others maintain that by diminishing the number of the grooves, the accuracy and range would be increased, and this has led to the opposite theory, that perhaps if anything, the plain surface of the bore should predominate over the grooved.
Form of early grooves straight.
The earliest rifles had two straight deep creases opposite to each other, the bullet being spherical, and furnished with small circular knots of lead, large enough to fill the creases.
Form &c., of ancient rifles.
The greater number of ancient rifles have a whole turn, with an odd number of deep and rounded grooves; hence we may infer these were considered the best forms.
Objects of rifling.
As accuracy of direction is the result of a spiral motion round an axis coincident with the flight of the bullet, communicated to it by the grooves, it is clear that the depth, number, and form of the grooves should be such as will hold the bullet firmly, and prevent all tendency to strip.
On the degree of spirality.
The degree of spirality should be sufficient to retain the projectile point foremost during the whole of its flight. It was at one time supposed that if the spiral turn was great, and the charge strong, the bullet would not conform, but strip, and that the same results would occur even with grooves but little curved. Unquestionably this would prove true if certain limits were to be exceeded. A false conclusion was built upon this theory, viz., that the greater the spiral turn the less the charge should be; and that therefore in rifles intended for war, the greatest initial velocity being required to produce the greatest range, the groove should have as little turn as possible; for extreme ranges have been obtained with Jacob’s, Whitworth’s, and Lancaster’s rifles; the first has a full turn in 24in. the second in 20in. Sharp twist and large charge not cause stripping.These rifles perform well with 90 grains of powder, and both Whitworth’s and Lancaster’s might even fire better were the charge of powder increased to 100 grains, the recoil might be objectionable while there would be no symptoms of stripping.
On depth of groove.
Great depth of groove can only be hurtful, owing to the difficulty of closing up all passage to the gas, which should not be allowed to escape round the bullet, as this would cause deviation and shorten range. Deep grooves become a receptacle for fouling, are difficult to clean; and high projections must offer great resistance to the atmosphere, and particularly to a side wind.
Patches.
When fustian or leather are used as patches, they receive and communicate the spiral motion to the bullet, without the zone of the projectile being at all indented, but in this case the spiral must be diminished, otherwise the bullet would not turn with the grooves. If the patches be made of a thick material, the grooves should be many, broad, and not too shallow, in order to receive the folds of the patch.
Shallow grooves best.
From our present amount of experience it seems safe to conclude that the shallower the grooves are the better, so that they perform their intended functions.
Proportion of groove to land.
It is now generally recommended that the grooves be made broader than the lands, i.e., that the rifling surface should predominate over the unrifled part of the bore. Shallow grooves with rounded edges, have the advantage of not leaving any angular traces on the surface of the bullet, besides they afford a greater facility for cleaning.
Circular grooving.
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.
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. Cause of canting.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.
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, Polygonal rifling.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.
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. By Captain Berner, 1835.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. By Mr. Lancaster.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.
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. Favors expansion.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. Assists aiming, firing two deep: when using bayonet.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.
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; Disadvantages of short rifles.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.