Heat gun

“ The investigation of the relations connecting the pressure, volume and temperature of the powder-gas inside the bore of the gun, of the work realized by the expansion of the powder, of the dynamics of the movement of the shot up the bore, and of the stress set up in the material of the gun, constitutes the branch of interior ballistics.
Fig. 3.
A gun may be considered a simple thermo-dynamic machine or heat-engine which does its work in a single stroke, and does not act in a series of periodic cycles as an ordinary steam or gas-engine. ”

“ All through the history of the development of machine guns the tendency has been toward lighter weapons, but it was not until the great war that serviceable machine guns were made light enough to give them great effectiveness and popularity. Such intense heat is developed by the rapid fire of a machine gun that unless the barrel can be kept cool the gun will soon refuse to function. The water jacket which keeps the gun cool proved to be the principal handicap to the inventors who were trying to remove weight from the device. ”

“ The gas-lever returning forces the cartridge home in the barrel and closes and locks the breech.
The hammer of the gun acts as the piston of an air-pump, forcing a strong jet of air into the chamber, and through the barrel, thus removing all unburnt powder, and thoroughly cleansing it. The metal employed is strong enough to resist the heaviest charge of nitro-powder, and the accuracy of its aim is not disturbed by the vibrations of rapid fire. It does not heat fast, so has no need of a water-jacket, any surplus heat being removed by a system of radiation. ”

“ When a projectile is thrown from a gun, although it is not heated appreciably, yet heat-energy represented by its velocity is absorbed from the expanding gases of the powder charge. When a 12-inch projectile weighing a thousand pounds is thrown from one of our long naval guns, it has a striking energy, fifty feet from the muzzle, of about 50,000 foot-tons—that is to say, it strikes with a force equal to that of 50,000 tons falling from a height of one foot, or one ton falling from a height of 50,000 feet. ”

“ Of course the fouler the gun the greater the evil that arises from its being left foul. In hot weather, barrels suffer infinitely more than in cold; [Pg 49] and in wet, than in dry. When dampness and heat are combined, the mischief is yet augmented; and, probably, the worst conditions that can be supposed are when, to dampness and heat, a salt atmosphere is superadded.
No man who owns a fine gun, which he values, ought ever to put it aside after use without cleaning, even if he have fired but a single shot. ”

“ The flame from the percussion powder is of that intense and vivid description, that if a charge of powder in the breech of a gun is loose, the flame will form a mass of condensed air round itself, and driving the grains of powder before it, prevent the immediate contact of the heat and the particles of powder, until the heat is expended ”

“ This gun was made by wrapping boiler plate around an iron bar, so as to form a cylindrical mass, the whole being brought to a welding heat in a furnace and then passed through rollers to unite it solidly. The piece was then bored and turned to the proper shape and dimensions. The projectiles for rifled guns were generally coated with soft metal, or furnished with an expanding base or cup of similar metal or papier maché ”

“ But later the48 Colt was formed with flanges, like the flanges on a motor-cycle engine, so as to increase the surface of the barrel. Of course, air-cooling is not so effective as water-cooling, but it is claimed for this gun, and for other machine-guns of the same class, that the barrel is sufficiently cooled for ordinary service. Although a machine-gun may be capable of firing many hundred shots per minute, it is seldom that such a rate is kept up very long in battle. Usually, only a few rounds are fired at a time and then there is a pause, and there is plenty of time for the barrel to cool. ”

“ The rapid fire and heating of the gun lessens the effective life of the weapon, due to the fact that the hot powder gases react more rapidly on hot metal than they do upon cold metal; hence a gun will last many rounds longer if fired at a slow rate than if fired at a rapid rate. ”

“ The great difficulty which has to be met in all single-barrel machine guns is the heating of the barrel. The 71⁄2 pints of water in the water-jacket of the Maxim gun are raised to boiling point by 600 rounds of rapid fire—i.e. ”

“ A bullet when fired from a rifle will fly into pieces after it has struck against the target, and if you quickly pick up one of these pieces you will generally find it quite hot. Whence comes this heat? The bullet, of course, was cold before the rifleman pulled the trigger.289 No doubt there was a considerable amount of heat developed by the burning of the gunpowder, but the bullet was so short a time in contact with the wad, through which so little heat would pass, that we must look to some other source for the warmth that has been acquired. ”

“ If fine and quick-burning powder be used in a long barrel, the powder is flashed into propelling gas, instantaneously, and beyond a certain length of barrel has no further expansive power, and the result is a friction of the charge in escaping, that affects the shot and consequently the pattern on the target. If slow burning powder be employed in a short barrel, the whole of the powder cannot be so instantly flashed into the propelling gas and some portion of it is, as a result, driven unconsumed from the muzzle of the gun. ”

“ Heating cordite and firing it hot undoubtedly does disturb its shooting qualities, but as far as we can see, not much more than gunpowder. I fear that we must always expect abnormal results with heated propellants, either gunpowder or cordite; and when fired hot, the increase in pressure and velocities will depend upon the heat above the normal or average temperature at which firing takes place. ”

“ In sporting guns snow may accidentally get into the muzzle or a lump of dirt may “somehow” get in so as to fill the bore, and when the gun is fired, it will probably, yes, most certainly be blown off or blown open where the obstruction exists; the muzzle of a gun being thrust into water for a couple of inches or more will have like effect. The gas formed by burning the powder finds no outlet of escape, and the whole expansive force concentrates itself on the weakest portion of the barrel, and as a result it is forced apart. ”

“ All three united masses are now cooled, when the fourth and widest cylinder of all, red-hot, is passed over these three inner tubes, and the whole gun is allowed gradually to fall in temperature. When this process is completed the inner parts of the gun, by virtue of the shrinkage in the metal as it cooled, are under severe compression, while the outer parts are in as extreme a state of stretch or tension. When such a gun is fired its inner cylinders oppose much greater resistance to the outward pressure of the exploding gases than did the walls of the old-time guns. ”

“ As the technique of forging large masses of steel improved, most nations adopted built-up (reinforcing hoops over a steel tube) or wire-wrapped steel construction for their cannon. With the advent of the metal cartridge case and smokeless powder, rapid-fire guns came into use. The new powder, first used in the Russo-Turkish War (1877-78) , did away with the thick white curtain of smoke that plagued the gunner's aim, and thus opened the way for production of mechanisms to absorb recoil and return the gun automatically to firing position. ”

“ As explosive charges more and more powerful were employed, these guns gave way, the pressure of the exploding gases stretching the metal at the bore to rupture, before the outer metal could add its resistance. A modern built-up gun is made up of a series of, let [253] us say, four cylinders: the first, of comparatively small bore and thickness, is innermost. It is cooled to as low a temperature as possible, when a second cylinder is slipped over it red-hot to form a tight fit. Both masses of metal are now slowly cooled, when a third red-hot, closely fitting cylinder is passed over them. ”

“ In the firing of explosives made according to the present invention, the gases produced at first are of a comparatively low temperature, as the substances apt to lessen the velocity of combustion, also tend to lower the temperature of the gases produced. This is of great consequence in respect of protecting the bore of the gun from erosion, for, with the high pressure during the first moments of combustion, any increase in temperature greatly increases the danger of erosion. ”

“ Since gas has proven without the shadow of a doubt, that it will produce more casualties for an equal amount of material transported to the front than any other substance yet devised, all troops using short range guns or mortars should be trained to fire gas whenever weather conditions are right. When weather conditions are not right, they should fire the other substances mentioned. The Livens’ projector with its 60 pound bomb, of which 30 pounds will be gas or high explosive, is a wonderful gun up to the limit of its range. ”

“ Finally, if the cast-iron shot of the 32-pounder were fired against armor-plate, it would lose, in breaking itself up, two thirds of its remaining energy, leaving at 1200 yards but 51 foot-tons for effective work; while with the modern armor-piercing shell the entire energy left at the end of the range is expended upon the armor-plate.
It will be seen then that the immeasurable superiority of modern guns is owing both to their great increase in energy and to their wiser disposition of that which has been attained. The gun has maintained fully during the century its primacy among naval weapons. ”

“ The spin of the bullet keeps its nose pointing forward. If it were not for the rifling, the bullet would tumble over and over, every which way, and it could not go very far through the air, to say nothing of penetrating steel armor. To gain the spinning-motion the bullet must fit into the barrel snugly enough to squeeze into the spiral grooves. Now there is another American machine-gun known as the Hotchkiss, which was used to a considerable extent by the French Army. It is a gas-operated gun, something like the Colt, and it is air-cooled. ”

“ By the time it is well warmed up, the hot air from the stove will have dried out every particle of moisture left in the barrel. If no stove is at hand, the last set of drying rags used must be plied vigorously up and down the barrel until it becomes quite warm from the friction. Drying is the most important part of cleaning, and if the least particle of moisture is left in the barrel it will be a rust spot the next time the gun is taken from its case. The gun may now be oiled, inside and out, with sewing-machine oil or gun-grease, which can be had in any gun store. ”

“ The breech arrangements must be such that they make an absolutely gas-tight joint, and such that the joint can be rapidly made, and that after having been subjected to the enormous pressure brought on it by the explosion, it must be capable of being as readily unmade, so that the breech may be opened.
To insure the true direction of the shot, the gun must be rifled, and means must be provided, as far as practicable, to neutralise the rush of powder gas and mitigate its erosive effects. ”

“ True; and the cause is quite apparent: the rapidity of combustion condenses the air so quickly, as to remove the grains of gunpowder liable to come in contact with the flame, and to form the condensed air into a line of demarcation: for heat cannot be taken up by the air quicker than the atmosphere will convey sound; and before the heat can evaporate the explosion is over, and is consequently noiseless. ”

“ But it must be always remembered that the object of the fire fight is to bring a concentrated and overwhelming fire to bear at the right moment on certain positions of the enemy, and when the moment arrives machine guns can and will use the most rapid rate of fire possible, which will be from 250 to 300 rounds a minute or equal to [8] that of 50 or 100 riflemen. Mere volume of fire, however, is useless without control, accuracy, and concentration, and it is here that the machine gun is so vastly superior to the rifle ”

“ All who have witnessed the performance of the 80-ton gun must have been surprised at the mildness of its thunder. To avoid the strain resulting from quick combustion, the powder employed is composed of lumps far larger than those of the pebble-powder above referred to. In the long tube of the gun these lumps of solid matter gradually resolve themselves into gas, which on issuing from the muzzle imparts a kind of push to the air, instead of the sharp shock necessary to form the condensation of an intensely sonorous wave. ”

“ The cooling of the barrel of a machine gun by air in place of the more usual water jacket is a problem of no mean difficulty. It is not ordinarily realised how great is the output of a machine gun in continuous firing expressed in horse power. Thus in the case of the M.VI service ammunition the muzzle energy is 2,000 ft. ”

“ The high rate of fire concentration of the bullet-sheaf, and the possibility of bringing several machine guns into action on a narrow front, enable great effect to be produced in a short time even at long ranges. When the front of the target is broken and irregular, the effect is reduced. A wrong sighting elevation or an imperfect observation of fire may render the fire completely ineffective. ”

“ A small part of the gas generated by the explosion of the individual cartridge operates the mechanism, discharging the bullet, throwing out the empty shell and making ready for the next shot.
A machine gun is designed to enable one man to fire the equivalent of a volley, or series of volleys, discharged by an entire platoon (one-third of a company) of infantrymen. As at present developed, it represents a step toward the evolution of a shoulder-rifle that will throw a continuous stream of bullets. ”