Lesmok Powder. It is unlikely that anyone who reloads ammunition will ever run into any of this powder but if the reader should by chance comc into possession of any of it, get rid of it quick. By getting rid of it 1 mean dump it on the ground and burn it, or throw it in the creek. This powcer is used today in loading .22 calibcr, rim-fire ammunition and it is probably the most dangerous powder to load that there is. Lesmok powder acts like semi-smokeless with respect to the fouling that it leaves in the bore of a firearm but that is as far as the similarity goes for Lesmok is a mixture of black powder and GUN COTTON". It ignites easily and can be fired by friction or by a blow. Even in the hands of those thoroughly familiar with it in the ammunition plants, flare-ups occur with it and it is only because of special precautions and safeguards that these are not serious.
Smokeless Powder This is the type of powder that is most widely used for hindloading ammunition as well as in ammunition manufacture. Any reloader who can follow simple directions and who is willing to stick to the more moderate charges of powder can use smokeless powders with safety and entire satisfaction, but when using full charges or departing from recommended loads in any detail, one's knowledge of powder can not be too complete.
Smokeless powders, unlike black powder, are chemical compounds rather than rr.cchanica! mixtures. No two powders are alike and as the chemical reactions and combinations that take place during the manufacturing process can not be controlled exactly, there is often a considerable
72 difference in the performance of two batches or lots of the same powder. The power ot powder is dependant upon the amount of nitrogen that it contains. In black powder» the nitrogen is contained in the potassium or sodium nitrate that forms a part of it. As dicse substances can be accurately measured and as their nitrogen content is definitely hxed, it is possible to get the same amount ot nitrogen into each batch of powder. This is not true of the manufacture of smokeless powder, the body of which is nitrocellulose. Nitrocellulose, as used in American powders, is cotton waste or linters nitrated by treating with nitric and other acids. After nitration, the acid is washed out by boiling in changes of water for several hours. The water is removed from the nitrated cotton first by centrifical wringing, then the remainder by forcing alcohol through the wet cotton, the alcohol displacing the water.
The nitrocotton is then reduced to a plastic gelatin-like condition by the use of suitable solvents in mixing machines during which process the stabilizing agents, salts, or deterrents are incorporated. Much of the solvent used is recovered and used over again.
The amount of nitrogen taken up by the cotton depends upon the strength of the acids used, as well as the length of time the cotton is exposed to the nitration treatment. Some of the nitrogen taken up by the cotton is lost in the later washing and boiling purification process. Large blends of the nitrated cotton are made so that the average nitrogen content is virtually the same from lot to lot.
The gelatinized nitrocellulose is squeezed through dies and formed into strings of a size suitable for the ultimate purpose the powder is to serve, either as a solid string or with a small hole through the center, after which it is cut into grains of the proper length and dried.
Smokeless powders are divided into two classes; nitrocellulose or single base powders which are of nitrocellulose with a stabilizer salts, deterrent, etc., and nitroglycerine or double base powders which arc made from nitrocellu-
73 lose also but with nitroglycerine added, with or without a stabilizer or deterrent. A stabilizer is an agent used to arrest any chemical action in the powder so that it will net deteriorate rapidly in storage; diphenylamine or crude vaseline being used extensively for this purpose.
There has been much argument over die relative merits of nitrocellulose and nitroglycerine powders, it being claimed that the latter are much more erosive than the former. This is probably true with powders containing a large percentage of nitroglycerine because of the high burning temperatures developed, but if the quantity of nitroglycerine is not large, there is little difference in the erosion caused by the two types of powder. When used in reduced loads, neither of these powders arc erosive. In making nitrocellulose powders, it is impossible by any practicable means to recover or drive off all the solvents and anyone opening a fresh canister of nitrocellulose powder will readily detect the strong odor of ether. The remaining volatiles, or solvent in the powder, will gradually evaporate and will do so more rapidly if the
powder be stored in a warm place. This changes the ballistic properties as the solvents act as a deterrent and their loss consequendy somewhat speeds up the burning rate or the powder and higher pressures will result. The reader should not be alarmed at this statement as our nitrocellulose powders will stand long storage under proper conditions.
Nitroglycerine powders, on the other hand, use a smaller amount of acetone solvent becaues of the solvent power of the nitroglycerine, and hence the grains are not apt to change due to solvent loss, no matter how long the powder is stored. Nitroglycerine powders are the easier of the two to ignite, they burn a little more uniformly, and because of iheir higher nitrogen content arc more powerful, which means that they can be used in smaller charges than nitrocellulose powders to develop the same ballistics. Because of their ease of ignition, nitroglycerine powders are not so susceptible to primer faults as other powders. The reader may suspect that I am prejudiced in favor of nitroglycerine 74 powders. I am and because I have always been able to get just a wee bit better results with them. It should be borne in mind, however, that one person's opinion doesn't prove a thing, nevertheless, it is perhaps significant that some of the new line of duPont powders contain nitroglycerine. And this after the long years xl\at the duPont boys have prcachcd about the horrors of nitroglycerine in powders, years, by the way, during which the duPont Co. made nothing but nitrocellulose powders. Well, they arc nicc boys just the same and the new powders arc excellent.
For many years much has been made of the erosive properties of nitroglycerin powders. It is true that nitroglycerine powder is more erosive than nitrocellulose powders but only when the nitroglycerine content is high. This is largely due to misunderstanding, and the fact that the corrosive effect of the older type primers was generally attributed to the erosive properties of the powder instead of to the primers where the fault actually lay.
Glycerin is just one of many substances that will take up nitrogen when treated with nitric acid. When nitro-glycerin is added to nitro-cellulose it simply increases the potentiality or nitrogen content of the resultant powder. If two charges of powder of equal volume, one containing nitroglycerin and the other being of straight nitro-cellulose, are fired in the same chamber under the same conditions, the powder with the higher potential will develop the greatest amount of heat. As heat is closely related to the subject of erosion, the powder of the higher potential will be the most erosive. This forms the basis of the statement that nitro-glycerin powders arc more erosive than nitro-cellulose powders, but the hitch comes in that the two kinds of powder are not loaded in equal volume. Because of the higher potential of double base powders, smaller charges of them arc required than single base powder to impart a given velocity to a bullet, and the pressures developed by the double base powders are frequendy less than those that must be developed by a straight nitro-cellulose powder to 75 obtain the same velocity. As the heat, or burning temperature produced, is influenced by the chamber pressure a double base powder will sometimes develop less heat and consequendy be less erosive than a straight nitro-ceiluiosc powder. The mere fact that a powder has nitro-glycerin in it means nothing in itself as far as erosion is concerned. The whole matter is one of potential or nitrogen consent and it is possible to produce a nitroglycerin powder of lower potential than a straight nitrocellulose powder.
The DuPont Company has for many years been identified with the manufacture of straight nitro-cellulose powders. Their new line of I.M.R. Powders are of this class and are excellent. Their new Pistol Powder No. 6, however, contains a small percentage of nitro-glycerin and this powder, because of its easier ignition and more uniform burning, is a considerable improvement over the now obsolete single base Pistol Powder No. 5.
The manufacture of nitroglycerine powder differs from the manufacture of nitrocellulose chiefly in the addition of the nitroglycerine. The proper amount is added to the dry nitro cotton, which is afterward worked thoroughly in a mixing machine. The mineral jelly or stabilizer is added while the batch is being mixed with the solvent, as with straight nitrocellulose powder. The general manufacturing process is the same for both and as this book pertains to the reloading of ammunition rather than to the manufacture of powder, the details of the process of making powders is purposely omitted.
Rate of Burning. Uniform ballistics or uniformity from one shot to another, can only be obtained by a uniform rate of burning of the powder. The rate of burning of any powder is therefore of the utmost importance in obtaining good accuracy and as the burning rate, especially of smokeless powders, is not fixed entirely by the composition of the powder itself, it is important that the handloader understands something of this.
76 If some black powder is ignited in the open air, it will burn with a quick flash, while smokeless powder burned in the open is consumed slowly. The rates of burning of these two classes of powder, when burned in the open, are obvious. When smokeless powder is loaded into a small arms cartridge and fired in the usual way, it burns quickly, therefore the rate of burning of smokeless depends upon the degree of confinement under which it is burned and this degree of confinement varies with the caliber and shape of the cartridge case and the amount of powder used, as well as a number of other things. In order to get this matter of rate of burning more firmly fixed in our minds, let us consider another simple example.
If a dry piece of string a foot long be ignited at one end, it will burn slowly until entirely consumed. Now, if we take a strip of pure nitrocellulose the same length as the string and ignite one end of it, it will be found to burn more rapidly than the string but, like the string, it will burn progressively from one end to the other. If a one foot strip of nitrocellulose having nitroglycerine incorporated in it is burned, it will be consumed more rapidly than cither the string or the pure nitrocellulose. In short, the three substances have different rates of burning. The rate of burning is merely the speed with which any substance is consumed by burning and is usually measured in feet or meters per second. It is governed by the amount of oxidizing agents present or, in other words, the amount of the substance that turns into oxygen when decomposed. It so happens that nitroglycerine is the only organic explosive that contains more oxygen than is necessary to burn it completely when excluded from the air and its incorporation in powder helps the combustion and increases the rate of burning, therefore, nitroglycerine powders burn more rapidly than nitrocellulose powders, all other things being equal. There are ways of controlling the rate of burning of powders other than by their chemical composition, as we will sec presently.
Getting back to our strips of powder, if twelve one inch J] pieces of powder arc all ignited at the same instant, they will be consumed in one twelfth the time required to burn a single strip one foot long. Twenty-four one-half inch pieces will burn in one-half the time required to burn the one inch pieces, etc. Therefore, the burning time is also affected by the size of the pieces of powder and the area that is ignited. The rate of burning is also affected by, not only the size of the pieces or grains of powder, but by their shape as well.
When a cartridge is fired the powder charge "explodes, the explosion being nothing more than rapid combustion or burning of the powder. In burning, the outer surfaces of the grains are consumed first, the grain decreasing in size as successive layers arc consumed until the grains arc entirely consumed. No matter how fast the powder burns, it always burns towards the center of the mass. Combustion is the oxidation of a substance and burning is rapid oxidation and is accompanied by the production of heat, and the rate of burning influences the heat or temperature produced. By way of example, we can consider a piece of wood. If exposed to the elements for a period of time it will decompose or rot. If ignited, it will decompose by burning, but the decomposition will be rapid and accompanied by the production of heat. The decomposition is, in both eases, due to oxidation and, believe it or not, the heat produced in both cases is the same. In the process of decay, the heat is given off so slowly and is so quickly dissipated that there is no measurable rise in temperature, as when burning takes place, and likewise, in both cases the decomposition starts on the outer surface and works toward the center of the mass.
Up until i860 gunpowder was used in solid granular form, or for artillery was pressed into solid blocks or cakes of various sizes and shapes. Powder of any kind burns from the exposed surface toward the center of the mass and the work that it can do depends upon the amount of gas given off. The area of a solid grain of powder is reduced and the grain hccomcs smaller and smaller until it is entirely con- 78 sumcd, conscqucndy it wiil give oH the greatest volume of gas at the insrant that the entire surface is completely ignited. When burned in a closed chamber, the expanding gasscs build up pressure that in turn forces the bullet or projectile forward. One or the laws of moving bodies having weight is that they can not be set in motion except at the expense of time and even aftsr the chamber pressure is above that recuired to overcome the weight and inertia of the bullet and impress it into the rifling of the barrel, a certain amount of time is required to accomplish this. After the bullet once commences to move, the space in which the gasscs are expanding continually and rapidly increases, as the bulle: moves along the bore. This additional space relieves the chamber pressure and it is desirable to have the gasscs reach their maximum pressure after the bullet is in motion. The ideal condition would be to have the pressure rise gradually until the bullet starts to move and to continue to rise, accelerating the bullet all the way to the muzzie of the arm. This would develop tremendously high velocities but it is impossible of accomplishment. On the contrary, the thing that must be avoided is having the pressures rise so rapidly that they exceed safe limits before the bullet has time to move, or to move far enough to leave enough space behind it for the gasses to expand in with safety.
Black powder is porous and if burned at too high pressure, the gasses will be driven through the grains causing almost instantaneous ignition and dangerous pressure. Smokeless powders, because of their close grained and horn like nature will stand higher pressures than black powder, but there are limits to the pressures that even they will stand.
As solid grains of powder evolve the most gas at the instant their entire outer surface is aflame, it stands to reason that in a closed chamber they develop the maximum pressure at this point. Powder charges do not ignite throughout at once. The primer ignites the rear of the charge, more or less of which burns, causing the development of heat and 79 pressure which ignite the remainder of the charge and accelerate the burning. We have seen by comparison that the pressure under which powder burns affects its rate of burning by comparison with powder burned at atmospheric pressure and v/hen fired in a gun; the higher the pressure, the faster the burning. Consequently, the rate of burning and the rise in chamber pressure is a progressive and accelerated phenomenon, each promoting the other. With solid grained powders the maximum pressure is reached quickly and the rapidly decreasing burning area of the charge causes it to fall off rapidly.
In the year i860. Col. T. J. Rodman conceived the idea of making artillery powder in the form of large washers that would just fit the chambers of the guns it was to be fired in. His theory was, that if the inside of the washers were ignited, the burning area of the charge would increase and there would be a constantly increasing volume of gas to accelerate the projectile which would increase the muzzle velocity; and practice bore out the theory. The form of the pressed powder soon changed but the principle was maintained and this was the forerunner of our present perforated powders. These powders burn both from the inside and the outside at the same time and as the outside area decreases, the inside area increases. Once a charge of tubular grained powder is fully ignited, the rate of burning is much more even than with solid grained powder but the grains burn from the ends and constantly decrease in length and it, like any other powder, is subject to the influence of the increased burning space due to the movement of the bullet. That tubular powder does burn from the inside as well as the outside is easily proven with a piece a couple of inches or more in length, such as Cordite, used by the British Army. Light one end of it and, by blowing hard, the fire on the outside can be blown out but the inside will continue to burn. Another example of this can be found in artillery powder which has a number of holes through it. When such powder is fired, the area of all the holes increases until they meet and the little triangular pieces that go are left are blown out of the gun. They can usually be found on the ground out in front of the gun and are known as "powder slivers."
By using perforated powder grains it was possible to get higher muzzle velocities than formerly because the more uniform burning gave a more sustained pressure and greater acceleration to the bullet, but the maximum pressure was still reached after the bullet had moved only a very short distance along the bore. Bailisticians were (and still are) working to delay the initial rate of burning of the powder until the bullet has moved further forward before "giving it the gun" in the form or accelerated burning of the charge and a greater gas volume. The increased space provided by the movement of the bullet would permit this to be done without causing dangerous pressure, but the trick was to do it. A considerable amount of progress has been made along this line since the World War. Some powders axe now coated or impregnated on the surface with substances that slow up their initial rate of burning. These powders are a little harder to ignite than plain burning powders but the surface of the grains burns slowly, relatively speaking, and builds up the chamber pressure more slowly, giving the bullet more time to move forward tnd allowing it to move farther forward before the flame reaches the unimpregnated and fast burning part of the grains. The greatest liberation of gas occurs after the bullet is in motion and while the position of the bullet at the time the highest pressure is reached, has only been advanced a fraction of an inch by the use of coated powders, even this small amount has resulted in a great increase in muzzle velociues.
It is unfortunate that the factors influencing the rate of burning of powder, and especially of smokeless powder, can not be explained in a few words but the phenomena are so involved and inter-related that it is difficult to explain some of them at all. The factorrs thus far discussed that aifcct the rate of burning may be summed up as follows:
1. The chemical nature of the powder itself. 81
2. The physical nature of the powder. (Hardness or porosity).
3. The degree of confinement under which it is burned.
4. The pressure under which it burns. (Related to confinement and temperature of burning).
5. The temperature of burning. (Related to confinement and pressure).
6. The size of the powder grains.
7. The shape of the powder grains.
Practically all of these factors represent things over which the handloader has no control whatever and the discussion of them therefore becomes purely academic. But there is one of them that can be and must be observed and controlled when reloading ammunition. I refer to the confinement of the charge.
Density of Loading. The relation of the volume of the powder chargc to the volume of the chamber it is fired in is called the density of loading and the more nearly equal the two become, the higher the density of loading is said to be. The two things that increase the density of loading or confinement of the charge when reloading ammunition sue: an increase in the quantity of powder used, and increasing the depth of seating of the bullet. The increased confinement alone from either of these causes will cause greater pressure to be developed in the chamber, to say nothing of that causcd by the additional gas liberated by the heavier charge of powder. When loading full charges of powder in any cartridge, any increase in the seating depth of the bullet over the recommended depth of seating should be accompanied by a corresponding decrease in the volume of the powder charge. With reduced charges, the depth of seating of the bullet is not important from a safety ttandpoint, provided the reduction in the charge is sufficient to off-set the additional space occupied by the bullet. 8a These two factors are not exactly in direct proportion, as any decrease in the charge is accompanied by a reduction in the total amount of gas given off, but a handloader will never gee into trouble by considering them as directly proportional.
Some cartridges have a low density of loading normally. The revolver cartridges, most of which were designed to use a large bulk of black powder, are examples of these. Loaded with smokeless powder, the charge occupies only a small part of the cartridge and with any normal charges and bullets, the depth of seating of the bullet is not critical and can be increased slighdy if necessary. When, however, deep seated wad-cutter bullets arc used, the confinement of the chargc becomcs too great and must be compensated for by a hollow in the base of the bullet, a reduction in the powder charge, or both.
Two other factors that affect the rate of burning and which may be listed in continuation of those previously mentioned are:
9. The volume of the powder chamber in relation to the sectional area of the bullet, ro. The shape of the powder chamber.
The sectional area of the bullet is direcdy related to the caliber. Because of the differences in volume and shape of different cartridges, the powder charges recommended for one will not give the same ballistics in another cartridge even though the other cartridge is of the same caliber. Likewise, if two cartridges had the same powder capacity and used the same bullets, charges would not be interchangeable in them because of differences in the shapes of the chambers for them. I know of no two cartridges in which this condition exists, outside of a few experimental ones and the comparison is offered only as a hypothetical one. Even a change in the angle of the shoulder of a botde-neck cartridge is sufficient to cause a considerable difference in the way the powder charge burns. By change in angle of the shoulder, I mean a deliberate and appreciable reform-83 ing of the shoulder and not any slight change that may take place when the case expands to the limits of a normal chamber.
Tolerance and Balance Point. If all powders burned exacdy alike and burned uniformly regardless of chamber volume, caliber, bullet weight, etc., we would only need one powder for loading all calibers of cartridges. But they don't. Each powder has its own peculiarities and limitations of ose, for reasons already explained and each one has a point in its pressure curve at which it burns best. This point is called the balance point.
When, for example, the bolt of a rifle is being designed, its outside diameter is fixed at a dimension that will permit it to work freely back and forth in its receiver. As it is very expensive to make mechanical parts to exact dimensions, some allowance must be made for slight variations that are bound to occur in commercial production, due to wear of the tools, etc. It is necessary, therefore, to establish the maximum diameter of the bolt at a point where it will not stick or fail to operate and the minimum diameter so it will not be a loose and doppy fit. This gives the workman a litde latitude to work in and still produce a satisfactory bolt. The permissible variations above and below the standard, or ideal, dimension are known as the tolerance. It is just so with smokeless powders and each one of them has a limit of pressure above and below the balance point, within which they will burn efficiendy and uniformly and this range of pressures is also called the tolerance.
If a powder is burned at a pressure below the lower limit of its tolerance, it may fail to burn uniformly and this will cause variations in velocity and poor accuracy. Even though the burning is fairly uniform, it may not be complete and port of the powder may break down into products that are injurious to the barrel. If the nitrates are not consumed, they can gather atmospheric moisture and form minute quantities of nitric acid which will cause rapid rusting, regardless of any magic non-corrosive primers. It is bad business to burn powders at pressures below the lower limits 84 of their tolerances, but it is not unsafe.
As pressures approach the upper end or the tolerance, the pressures arc still safe, even though they may be high, but they are approaching a pressure level at which they will burn erratically. The upper limit of the tolerance does not represent a point which, if exceeded slighdy, will cause bursting pressures. It docs represent a point beyond which the pressure developed can not be predicted with any degree of certainty. When this point is exceeded and whether the excess pressure is due to too much powder, too hot a primer, too large or hard bullet, or a bullet that is too heavy or too deeply seated for the charge, the pressure and velocity will become erratic. Loads developing pressures toward the upper limit of the tolerances arc known as "maximum permissible loads". They are not to be confused with maximum loads, about which more and very bad things will be said later. Erratic pressures arc jumpy, uncertain pressures. A person may exceed the maximum permissible load for a certain powder and cartridge and apparendy get away with it, shooting his ammunition in blissful ignorance of the way the pressures are jur.-.ping around. Then, for no apparent reason, one goes sailing up to the sky and he finds himself with his rifle in two pieces, one in each hand. Or maybe somebody else finds him. "Why! I can't understand it! I have been using that load for two years and am very careful about loading it—weigh the powder and bullets 'n every thing 1" Have you ever heard it? Of course he can't understand it. If he knew enough about powder to understand it, he wouldn't have used the load in the first place.
The tolerance of a powder, unlike that of the rifle bolt referred to previously, must be determined after the powder is made. When a new lot of powder is made, a charge, pressure and velocity curve is established to determine its ballistic properties. Assuming that the new powder is an attempt to duplicate a previous lot, the ballistic records of the previous lot are referred to as a guide to the selection of 85 a charge to start with. From three to five cartridges, depending upon the caliber of the cartridge, the practice of the laboratory, or expediency, are loaded with a very moderate charge and are fired for pressure and velocity. The mean or average of the pressure and velocity readings for this series of shots are plotted as two points on cross section paper. These results arc compared with the firing data of the previous lot for similarity, or lack of it, and another somewhat higher charge is determined upon for the next series of shots, the mean results of which are plotted as a second pair of points.
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