Explosives for large guns.
We present some extracts from an article in the North American review by Hiram Stevens Maxim, the highest authority on the subject:
The properties of nitro-glycerine were for many years but imperfectly understood.
It was said of it that if you wished it to explode it was impossible to make it do so; if you handled it with great care and did not wish it to explode it was almost sure to go off; sometimes it could be set on fire, and would burn very much like a slow fuse, while again the least jar would cause the most frightful detonation.
Evidently such an agent was not suitable for use in fire-arms, and it was only after Nobel's discovery that nitro-glycerine could be gelatinized with collodion cotton (di-nitro-cellulose) that engineers began to experiment with a view of using this high explosive in projectiles.
The naval and military engineers at Shoeburyness were among the first to conduct experiments, and it was found that when sufficient collodion cotton was employed to make the compound about the consistency of soft rubber, it could be fired with a comparative degree of safety from ordinary guns, providing, of course, that.
the powder charge used as a propellant was not too violent.
Large numbers of rounds were fired under apparently identical conditions, with the result that perhaps 99 per cent. passed harmlessly out of the gun, while about 1 per cent. exploded in the bore of the gun, completely demolishing it.
Another source of danger, especially when compressed gun-cotton is employed in rifled cannon, arises from the quick and violent twist given to the projectile,. which rotates the case or shell, without rotating the bursting charge.
This I obviated by dividing the interior of the shell into numerous compartments.
Still no one could be persuaded to use my torpedo-gun.
The next step was the Zalinski gun. This had been made and tested in the United States, when it was found that large charges of high explosives could be thrown considerable distances from an airgun.
One of these guns was brought to, England and fired at Shoeburyness.
It was said at the time that three shots fired with the gun firmly locked in a stationary position landed in the same hole in the mud. The accuracy was admitted to be remarkable, but the velocities were so low, the range so short, and the trajectory so high, that it was almost impossible to hit the target when the gun was fired from a ship.
It was even said that if the gun were properly aimed from a ship and the trigger pulled, the barrel, on account of its great length, would move sufficiently after the trigger was pulled and before the shot left the gun, to throw the shot completely off the target.
Still, it was believed that under certain conditions the gun might be useful for fortifications.
In any compressed air-gun of the Zalinski type, it will be evident that an increase in the atmospheric pressure is not attended by a corresponding increase in the velocity of the projectile, because the higher the pressure of the air the greater its weight and; density, so that when the pressures are
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increased, we will say from 2,000 to 3,000 lbs. per square inch, the actual velocity of the projectile is only slightly increased.
It occurred to me at that time that if the pressure could be increased without increasing the weight or density of the air a great improvement would result.
I therefore constructed a gun in which I used only 1,000 lbs. pressure per square inch.
The gun being loaded, in order to fire the trigger was pulled, which acted upon a large balance-valve which suddenly sprang open; the projectile was then driven forward.
When it had moved from 2 to 3 calibres, the charge of gasoline and air was ignited, and while the projectile was still moving forward, the fire ran back into the chamber, constantly raising the pressure, so that by the time the projectile had reached the muzzle of the gun the pressure had mounted from 1,000 to 6,000 lbs. per square inch.
and the result was a comparatively high velocity with a short barrel.
This gun was fired a great number of rounds in 1888, and found to be quite reliable.
The first smokeless powder that I made in England was made in exactly the same manner as the French.
I had obtained a quantity of true gun-cotton—that is, tri-nitro-cellulose (known sometimes as insoluble gun-cotton because it cannot be dissolved in alcohol and ether like collodion cotton, di-nitro-cellulose). Some of this powder, when freshly made, produced fairly good results, quite as good as those produced by the French powder, but upon keeping it for a few months the grains lost their transparency, became quite opaque and fibrous, and it then burned with great violence.
Investigation showed that about 1 to 2 per cent. of the solvent was still in the powder when the first tests were made, whereas the drying out of this last trace of solvent had completely changed the character of the powder.
I then added to this powder about 2 per cent. of castor oil, with the result that the castor oil remained after the solvent had been completely removed, so that the powder would keep any length of time— indeed, powder made at that time (1889) is quite good to-day.
But I wished to produce still higher results.
I believed that if the nitroglycerine and the gun-cotton were intimately combined an explosive wave would not pass through the mixture, and experiments revealed that I was quite correct.
All mixtures of from 1 per cent. to 75 per cent. of nitro-glycerine were experimented with, the result being that from 10 to 15 per cent. was found to be the best, everything considered.
The greater part of the smokeless powders employed to-day consist of a mixture of nitro-glycerine and gun-cotton.
The mixing is brought about by the agency of acetone, a species of alcohol which dissolves both gun-cotton and nitro-glycerine.
When a small quantity of this spirit is present, the mass is of a semi-plastic consistency, and may be squirted or spun through a die by pressure, in the same way that lead pipe is made.
The first powder experimented with was drawn into threads and called by the British government “cordite.”
This was found to work admirably in small-bore ammunition, but when it came to a question of larger guns it was found advantageous to form the powder into tubes with one or more holes.
By increasing the number of perforations, it was found that a powder could be made which, instead of burning slower and slower as the projectile moved forward in the gun, would cause the development of gas to increase as the projectile moved forward with accelerated velocity in the bore.
This was exactly what was required, and led to my patent on progressive smokeless powder.
In the olden time, when guns were not rifled, and spherical shots were employed with a powder charge of about one-eighth of the weight of the projectile, the erosion caused by the gases passing the projectile was so small as to be considered a negligible quantity—in fact, its existence was practically unknown to the majority of artillerists at that time, but upon the introduction of rifled guns with elongated projectiles and heavy powder charges erosion became a serious obstacle, which increased as the powder and range of the gun increased.
Large guns made in England from ten to fifteen years ago, using black or cocoa powder with projectiles of 3 or 4 calibres, and having a velocity rather less than 2,000 feet per
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second, were destroyed after firing from 300 to 400 rounds.
When the velocities were increased to about 2,200 feet it was found that the wear was about four times as great, while some very powerful guns made in France were completely worn out after firing sixty rounds.
With smokeless powder, which gives a still higher velocity to the projectile, the erosion is still further increased, so that in some cases I have known guns to be destroyed after firing only a few rounds.
In order to obviate this trouble we have provided the projectiles with what might be termed an obturating band; that is, just behind the copper driving band we have placed a semi-plastic gas check.
Behind it is placed what might be termed a junk ring, arranged in such a manner that when the gun is fired the junk ring moves forward and subjects the gas ring to a pressure 20 per cent. greater than the pressure in the gun—that is, if the pressure in the gun amounts to 14 tons per square inch the pressure on the gas ring is about 17 tons to the square inch.
This is found to completely stop the passage of gas between the projectile and the bore of the gun; so we are now able to fire large guns many hundreds of rounds with full charges before any perceptible wear takes place in the barrel.
This will enable our naval authorities to practise gunnery to almost any extent without the danger of wearing their guns out, and it is believed by many that in the near future no large guns will be fired on shipboard without the employment of the obturating gas check.
