Any firearm is really a machine for controlling the application of force which propels the bullet, or shot charge, through the air. The force necessary for this propulsion is generated by the very rapid production of gases resulting from the combustion of the powder charge; and on this account all powders which are used in firearms are termed propellants*
(A) Types of Rifle Cartridges i, rim-fire Long Rifle; 2, -300 Rook Rifle, straight and rimmed case; 3, »303 Mark VII, bottle-necked rimmed case and pointed bullet; 4, -303 Mark VI, bottle-necked rimmed case and round-nosed bullet; 5, -425 Sporting Rifle, bottle-necked rimless case and capped expanding bullet; 6, »373 Magnum Sporting Rifle, bottle-necked belted rimless case and solid bullet; 7, »577 Sporting Rifle, tapered rimmed case and solid bullet
(B) Types of Pistol and Revolver Cartridges
1, 7*63 mm. Mauser Self-loading Pistol, bottle-necked rimless case; 2, 6*5 mm. Bergmann Self-loading Pistol, bottle-necked tapered case without any sort of rim; 3, -380 Revolver Cartridge, straight rimmed case; 4, #4< Self-loading Pistol Cartridge, straight rimless case; 5, »455 Service Revolver Cartridge, straight rimmed case; 6, 7*62 mm. Nagant (Russian) Revolver, bottle-necked rimmed case with a nickel-jacketed bullet loaded with its nose level with the mouth of the case; the bullet is held in position by "stabbing M as can be seen
The subject of propellants is big and complex, and I will make no attempt to deal with it here beyond stating a few bare facts.
The propellants used in firearms are either Black Powder or Smokeless Powders. The latter are distinguished as Nitrocellulose Powders if nitroglycerine is not an ingredient; and Nitroglycerine Powders if nitroglycerine is an ingredient. All smokeless powders contain nitrocellulose.
Black powder consists of jet black, and rather shiny, grains.
Although black powder has been in use for about six centuries, and although improved methods of manufacture have naturally led to greater efficiency in action, its composition has remained practically the same in all countries.
In Great Britain this composition is:
Potassium Nitrate (Saltpetre) . 75 per cent. Charcoal . . . . 15 „ „ Sulphur . . . . 10 „ „
The rate of burning is controlled by varying the size of grain, and the size of grain is denoted by a number.
The appearance of black powder is unmistakable to an experienced investigator, but if there is doubt a few grains can be placed on the tongue when the "salty" taste of the saltpetre will be noticed at once.
The real test, however, for black powder is to try to ignite a small heap of it with a match. It cannot be ignited with the flame, but will ignite immediately on being touched with the glowing end of a match left after the flame has been blown out. When black powder is used in a firearm it is unmistakable owing to the heavy smoke which is produced.
Powders based on nitroglycerine, nitrocellulose, or on a mixture of these two substances are almost entirely smokeless in action. They are all given the generic term of nitro powders and are legion in number.
All nitro powders used in rifles, pistols and revolvers are "gelatinised" powders, that is they are made by forming a "dough" into sticks or grains.
Cordite is the British service propellant and consists of nitroglycerine, guncotton and mineral jelly. It is of a brownish-yellow colour and in high-power rifle cartridges the charge consists of small sticks which are cut to a length to fit into the case. These "sticks" are really tubes in some cases, as a small hole will be noticed running up the middle of each. Such cordite is known as M.D.T. (modified and tubular).
Mark I cordite consists of solid cords, and in this the proportion of nitroglycerine is higher than in Cordite M.D. (modified) or in Cordite M.D.T., but the colour is very much the same, namely a brownish yellow.
"Pistol Cordite" consists of small cylindrical grains of cordite, about -05 of an inch long, and is frequently used in service revolver cartridges and light rifles of the "rook and rabbit" class.
Moddite and Axite were two propellants made before the first great war which were both so similar to cordite in composition, behaviour and appearance that they could be regarded as cordite for all practical purposes.
Nitrocellulose powders are always granular. The grains sometimes consist of small cylinders, and sometimes of thin square flakes, when they are called "Flake" powders. They are frequently coated with graphite which gives them a dark grey colour. When not so coated the colour may be almost anything that the manufacturer fancies, but is usually a light grey.
Neonite is a British flake nitrocellulose powder which cartridges and their components 33
is now extensively used in revolver and pistol cartridges, and of a greenish grey colour.
Shotgun Powders.—Black Powder is seldom used in shotgun cartridges in Great Britain, although it is still loaded fairly extensively for native use abroad. All other shotgun powders are more or less smokeless and based either on nitroglycerine, nitrocellulose, or both, as are rifle and pistol powders. But they differ from these last in that they are also classified into "Bulk" and "Dense" powders.
The term "bulk" was applied to shotgun powders when black powder was replaced by smokeless powders. The standard charge for an ordinary 12-bore game gun was 3 drachms of black powder, and for convenience in loading powder measures were invariably used which held a volume of black powder which weighed exactly 3 drachms.
Smokeless powders were found to be much lighter in density than black powder, yet for purposes of general convenience in loading they were so standardised in manufacture that the same measure could be used for them as for black powder. In other words, the charge of smokeless powder was the same as that of black powder when measured by volume, or bulk, but not when measured by weight. The term "bulk" then came to be applied to all smokeless powders which could be loaded correctly with a black powder measure, and it has been in general use ever since.
Bulk powders are designated by the weights of charges which fill a 3-drachm black powder measure. For instance, there are 33-grain powders, 36-grain powders and 42-grain powders; and these designations mean that the volumes of the powders in question which exactly fill a 3-drachm black powder measure weigh respectively, 33, 36 and 42 grains.
Powders which cannot be loaded by bulk are termed "Dense" powders.
For a good many years there has been a tendency in both England and America, as well as on the Continent of Europe, to replace bulk shotgun powders by dense. The only advantage of a bulk powder is that it permits the use of the old standard black powder measures for the loading of cartridges. The disadvantages are first that in order to make the powder to "bulk" in correspondence with black powder it must contain in its composition a proportion of "dead" substances which do not help its efficiency as an actual propellant or explosive. Following from this is the increased cost in manufacture, which entails such additions as well as the care to ensure that definite amounts of powder can be loaded as correctly by volume as by weight. Since 1945 costs of manufacture throughout the world have increased so much that bulk powders are steadily being replaced by dense in all countries where small arms powders are manufactured, and the only change in the procedure of loading shotgun cartridges that is really needed to meet this steadily increasing use of dense powders is to use "hoppers" or powder measures of a size corrected to hold the proper weight of a dense powder.
The term "Bulk" and "Dense" really apply only to shotgun powders, since all nitro powders made for rifle and pistol cartridges are invariably dense powders.
But there are further definitions of powders which are regularly employed and which should be understood, and to sum up the following definitions are given—
Nitroglycerene Powder.—A nitroglycerene powder is one which contains nitroglycerene.
Nitrocellulose Powder.—A nitrocellulose powder is one which contains nitrocellulose but no nitroglycerene.
(A) All-Metal Cartridges with fully crimped Closures
The two larger diametered cartridges on the left are original F.N. 2-inch r.inc cartridges. The other5 are British solid drawn brass .410 cartridges. On the extreme right there is a tired case of one oi these cartridges which shows the total length of the case
(B) British paper-tubed fully crimped Cartridges
On the left there is an empty unfired case. Next is a loaded case with the top nartially closed by the first stage of the crimp. The three cartridges on the right are finished ana the shortened length of the case caused by the crimp closure as well as the appearance of the closure and the method of marking the shot size are clearly visible
Double Based Powder.—A powder which contains both nitroglycerene and nitrocellulose.
Gelatinised Powder.—A gelatinised powder is one which has been made by forming a dough or gelatinised mass which is then made into small grains. The dough is made by treating a nitrocellulose mixture with solvents in a mixing machine. This resulting dough-like mixture is pressed into tubes or rods or rolled into sheets from which solid grains are cut or stamped out.
Porous Gelatinised Powder.—A gelatinised powder which has been made porous during manufacture by adding small particles to the nitro-cellulose mixture which is made into a dough. These small particles are of a substance which can afterwards easily be dissolved out, and they are thus removed at a later stage in the process of manufacture, so leaving tiny pores in the powder grains. These pores are very small and cannot always be readily seen with a pocket lens, although they are rendered visible easily with a microscope. But they are large enough to be penetrated easily by the hot powder gases under the pressure which is generated in a gun-barrel, and, therefore, the grains are easily burnt up.
If the grains are only partially burnt the pores are easily seen as relatively big holes. (See Rottweil and Cooppal Excelsior grains in Plate VIII.)
Non-Porous Gelatinised Powder.—A powder which has not been made with small pores in the grains and which cannot, therefore, be penetrated by the hot powder gases. Such powders burn only on the surface or at the edges.
If the grains are only partially burnt the surfaces appear uneven and the edges irregular. (See Neoflak Modified, Neoflak and Mullerite grains in Plate VIII.)
Fibrous Powder.—A powder is called Fibrous when it is made from nitrocellulose and the grains appear as very small balls of tightly rolled cotton wool. Actually these powders are made by rolling a mixture of finely divided nitrocellulose up into grains which explains their appearance and their fibrous nature can easily be seen when examined under a pocket lens. These fibrous hardened grains can be broken down by rubbing in the palm of the hand.
Powders used in small arms, particularly shotgun powders, are so numerous that it is impossible to give a complete list of the different powders made in all countries, especially as changes are constantly being brought about both in the size and appearance of the grains. Some can be identified with comparative ease and certainty by visual examination; but even for this considerable experience is necessary as well as an adequate collection of named samples which can be used for purposes of checking and comparison. Other powders are so similar, one to the other, that a quantative analysis by an expert explosives chemist may be necessary to identify them with certainty. In forensic work the actual identification of some particular powder will not often be necessary, or of such importance as matching beyond all doubt one sample with another, and if such identification is really necessary it is essential that a real expert in powders should be consulted.
But the identification of partially burnt powder grains may become a matter of vital importance, since such grains may be found round the entrance hole of a wound, and it will obviously help if the type of powder can be identified from these unburnt grains. This particular problem, however, will be dealt with in Chapter V.
In British high-power rifle cartridges either some form or other of cordite is used, or else a granular nitrocellulose powder comprising small cylindrical grains of a dark grey colour.
Photo-micrographs of partially burnt grains of five different types of shot-gun powders all taken at a magnification of x io diameters
Top Row: "Crime" Powder. Second Row: Ncoflak Modified. Third Row: Neoflak. Fourth Row;
Rottweil. Fifth Row: Coonpal Excelsior. Sixth Row: Mullerite The similarity between the appearance of the grains in the Top and Second Row together with the diflerence in the appearance of the grains in the Top Row and all those in the Third, Fourth. Fifth, and Sixth Rows are sufficiently pronounced to identify the "Crime" powder as Neoflak Modified
In British revolver and pistol cartridges either pistol cordite, or neonite.
The appearance of these powders has already been described.
Foreign high-power rifle and pistol and revolver cartridges are almost all loaded with some type of granular nitrocellulose powder.
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