| A. Introduction
2A1. Fundamental ideas
The value of ordnance lies in its power to destroy. This depends on the use of explosives more than on any other factor. The gun projectile reaches the target because of the energy released by the propellant charge; it disrupts defenses and harasses enemy personnel primarily to the extent that the bursting charge it carries is effective. Mines and torpedoes tear holes in the steel skin of a ship because of the force released by the great quantity of high explosives they contain. One of the most important aspects of the history of ordnance is the development of explosives from the weak and unstable gunpowder of Roger Bacon to the highly specialized explosives of today. The latest discovery was nuclear fusion and its release of tremendous explosive energy.
The present chapter is confined to a discussion of the characteristics, use, and handling of chemical explosives currently used in the United States Navy.
B. Explosive Reactions
Most people know that chemistry and physics are sciences which deal with matter and energy, and that matter and energy are closely related. Chemistry deals with the composition and changes in composition of substances, and a chemical change is a definite permanent change of certain properties, with the formation of new substances. Such changes are always accompanied by a gain or loss of energy. Whenever a chemical change takes place, there is a chemical reaction.
An explosion is one kind of a chemical change. It is a rapid and violent release of energy, produced by the rapid chemical decomposition and oxidation of any of several substances called explosives. It is true, of course, that the term explosion is often applied to violent releases of energy not involving explosive substances. In the explosion of a boiler, for example, the water (or steam) is not considered an explosive substance. But in this text, the term explosion is reserved to describe a chemical reaction that produces heat, and forms decomposition products, some or all of which are gases. An explosion is simply a rearrangement process, whether it is a rapid burning (as in some explosives) or a violent detonation (as in others).
Many modern explosives are based on chemical compounds containing nitrogen. Though nitrogen itself is chemically a relatively inert gas (it makes up most of the atmosphere), its oxidized form combines with other elements to form (among other products) more or less unstable chemical compounds which explode violently in the sense of the word as used in this text. This violent explosion (or decomposition and rearrangement) liberates large amounts of heat and produces large volumes of gases, which expand and occupy a great deal more space than the explosive did originally. An explosive reaction, therefore, always produces a sudden rise in pressure because of the formation of gases and their expansion by the heat liberated in the reaction. The sound and shock waves associated with an explosion are caused by this sudden rise in pressure.
It will be seen later that the rise in pressure may be comparatively slow or it may be so fast as to be almost instantaneous. But whether an explosion is fast or slow, it is a decomposition and rearrangement of substances and is therefore basically a chemical reaction.
For a discussion of atomic explosives, see volume 2 of this course.
2B2. Classification of explosive substances by reaction
Explosive substances include a large number of chemical compounds and mixtures. The greater number of military explosives fall into the following groups.
1. Explosive inorganic compounds. Lead azide is an example. Lead azide is used as the detonator in major-caliber fuzes, because its relatively low sensitivity permits the projectile to penetrate armor plate before the detonator functions.
2. Explosive organic compounds. In this group are the main military explosives. It includes nitrated derivatives of the carbohydrates (example: nitrostarch), and the nitrated derivatives of aromatic compounds, such as trinitrotoluene (TNT). The prefix nitro appears in the chemical names of several modern explosives, such as nitroglycerin, nitrocotton (the main component of smokeless powder), trinitrophenol (picric acid), and others.
3. Mixtures. This group includes mixtures formed by oxidizable and oxidizing bodies, solid or liquid, neither of these being explosives separately. Black powder is an example.
With regard to their type of reaction, however, explosives are classified as low (sometimes called burning or progressive) and high. This speed of burning or breaking up is considered the most important characteristic of an explosive substance.
A low explosive reaction is a true burning, which proceeds from point to point throughout the explosive substance, accelerated by the heat and pressure produced. Since a low explosive burns, it builds up pressure comparatively slowly, delivering a powerful but controlled push to the projectile, following through all during the projectile’s movement in the bore. Low explosives always contain a source of oxygen, and one or more combustive elements such as carbon or hydrogen. Because the explosive itself contains all the oxygen required for the reaction, the combustion can proceed without support from outside sources. Among the well-known burning explosives are black powder, ballistite, United States Navy smokeless powder, and Cordite.
Note: The term “low explosive” is no longer recognized by specialists as a distinctive term denoting a class of explosives, since many explosives of this type can be made to react like high explosives under certain conditions. However, the term continues to be used in this text because the classification, though perhaps no longer accurate enough for the specialist, is still a useful concept for the student.
High explosives give rise to reactions that proceed almost instantaneously throughout the explosive mass. They produce their pressure (with a shattering effect) almost instantaneously, in what is called a detonation. If a high explosive were to be used for a propellant in a cartridge case, all its energy would be used in shattering the gun before the projectile had a chance to move. Combustible elements and oxygen are usually, but not always, present in high explosives. These substances are characterized by unstable molecules that include weakly attached parts such as nitrate and nitro groups. The initiating impulse brings about a breaking down of the chemical bonds, and a molecular rearrangement occurs so rapidly that the evolution of hot gases is almost simultaneous throughout the mass. Some examples of high explosives are: TNT, RDX, HBX, tetryl, and ammonium picrate.
Primary explosives, like high explosives, detonate when initiated, but they are extremely sensitive and, as a class, have less power, weight for weight, than high explosives. However, there is no abrupt, sharp dividing line between primary and high explosives. Primary explosives are used chiefly to initiate explosive trains. Primary explosives in current use in the Navy include lead azide, mercury fulminate, lead styphnate, diazodinitrophenol (DDNP), tetracenc, and nitromannite.
2B3. Classification of explosive substances by composition
From the standpoint of their composition, explosives may be divided into explosive mixtures and explosive compounds.
Explosive mixtures are an intimate mixture of distinct substances, carefully prepared and mechanically conglomerated in varying proportions. Explosive mixtures must have some oxygen supplier such as nitrate or chlorate, and some combustible such as carbon or sulphur. Black powder is a typical example of an explosive mixture.
Explosive compounds are homogeneous substances whose molecules contain within themselves the oxygen, carbon, and hydrogen necessary for combustion. Whereas the characteristics of explosive mixtures can be varied by changing the proportions of the components, the elements constituting an explosive compound are always present in the molecules in the same proportions. Therefore, the nature of the explosive compound cannot be changed by varying the quantities of the constituent elements. Explosive compounds of different characteristics can be obtained, however, by nitrating the basic substance to different degrees. Explosive compounds consist very largely of organic compounds (hydrocarbons) into which nitric (-NO2 or -0-NO2) groups are introduced by the process of nitration. Examples of explosive compounds produced by nitration are cellulose nitrate, nitroglycerine, TNT, ammonium picrate, tetryl, and RDX.
2B4. Characteristics of explosive reactions
The most important characteristics of explosive reactions are as follows:
1. Velocity. An explosive reaction differs from ordinary combustion in the velocity of the reaction. This is also the basis for differentiation between high and low explosives. The velocity of combustion of explosives may vary within rather wide limits, depending upon the kind of explosive substance and upon its physical state. The burning rate of colloidal cellulose nitrate powders used as propellants in modern guns is in the order of 24 centimeters per second at average gun pressures, whereas the velocity of reaction of high explosives ranges from about 2,000 to 8,500 meters per second.
2. Heat. An explosive reaction is always accompanied by the rapid liberation of heat. The amount of heat represents the energy of the explosive and hence its potentiality for doing work. It may be supposed that the quantity of heat given off by an explosive reaction is large, but this is not necessarily the case. A pound of coal, for example, yields five times as much heat as a pound of nitroglycerine. However, coal cannot be used as an explosive, because it fails to liberate heat with sufficient rapidity.
3. Gases. The principal gaseous products of the more common explosives are carbon dioxide, carbon monoxide, water vapor, nitrogen, nitrogen oxides, hydrogen, methane, and hydrogen cyanide. Some of these gases are suffocating; some are actively poisonous. The gases from low explosives are rarely dangerous, since they usually escape at once into the open and are dissipated and diluted with air. Generally speaking, the commonly used high explosives produce a large proportion of noxious gases, which are particularly dangerous, since under normal conditions of use these gases do not dissipate rapidly. Projectiles filled with high explosives often burst after penetration into confined spaces from which the gases are not easily evacuated.
Some of the gaseous products of explosive reactions are themselves flammable, or form explosive compounds with air. Among these are hydrogen, carbon monoxide, and methane. The flame at the muzzle of a gun when it is fired results from the burning of these gases in air. Similarly, residues of the explosive mixture remaining in the gun, or blown back by adverse winds, have been known to ignite when brought into contact with air as the breech is opened. The ignition may come from the high temperature of the gas or from the burning residue in the gun bore. The resulting explosion may transmit flame to the rear of the gun, producing what is called a flareback. Flare-backs may ignite fresh powder charges being served to the gun. This danger has led to the adoption of gas-expelling devices on guns installed in enclosed compartments or mounts.
4. Pressure. The high pressure accompanying an explosive reaction is due to the formation of gases which are expanded by the heat liberated in the reaction. The work which the reaction is capable of performing depends upon the volume of the gases and the amount of heat liberated. The maximum pressure developed and the way in which the energy of the explosion is applied depend further upon the velocity of the reaction. When the reaction proceeds at a low velocity, the gases receive heat while being evolved, and the maximum pressure is attained comparatively late in the reaction. If, in the explosion of another substance, the same volume of gas is produced and the same amount of heat is liberated, but at a greater velocity, the maximum pressure will be reached sooner and will be quantitatively greater. However, disregarding heat losses, the work done will be equal. The rapidity with which an explosive develops its maximum pressure is a measure of the quality known as brisance. A brisance explosive is one in which the maximum pressure is attained so rapidly that the effect is to shatter material surrounding it or in contact with it.
2B5. Sensitivity of explosive substances
The amount of energy necessary to initiate explosion is the measure of the sensitivity of the explosive. Sensitivity is an important consideration in selecting an explosive for a particular purpose. For example, the explosive in an armor-piercing projectile must be relatively insensitive; otherwise the shock of impact would detonate it before it had penetrated to the point desired. Again, if the molecular groups in the explosive are in such unstable equilibrium that the reaction starts spontaneously, or in response to a slight blow, the substance can have no practical application whatever.
It was originally considered that the power of an explosive was measured by the sensitivity and that the most powerful explosives were the most sensitive. Investigation has proved that this is not true. TNT is a good example of a very powerful explosive which under ordinary circumstances requires a severe shock to initiate explosion.
2B6. Initiation of explosive reactions
An explosive reaction is initiated by the application of energy. The preferred method of initiation depends on the characteristics of the individual explosive. However, in accordance with the dual classification of explosives into low and high, the two methods of initiation commonly distinguished are:
1. By heat. Low explosives are commonly initiated by heat; and the resulting reaction is a burning process, which occurs on the exposed surfaces of the substance and progresses through the mass as each layer is consumed. Some high explosives will react when sufficient heat is applied, especially if heat is applied suddenly throughout the mass. Initiation by percussion (direct blow) or by friction is simply another form of initiation by heat derived from the energy of the blow or friction.
2. By shock. High explosives, such as the main charges of mines or torpedoes, in general require the sudden application of a strong shock or detonation to initiate the explosive reaction. This detonation is usually obtained by exploding a smaller charge of a more sensitive high explosive that is in contact with or in close proximity to the main charge. The smaller charge can readily be exploded by heat or shock.
It has frequently been demonstrated that detonation of an explosive mass can be transmitted to other masses of high explosive in the near vicinity, without actual contact. The second explosion occurring under these conditions is said to be initiated by influence, and it has been generally accepted that the initiating effect is the result of the passage of an explosive percussion wave from one mass to the other. The second explosion is called a sympathetic explosion. The distance through which this action may take place varies with the kinds of explosive, the intervening medium, and certain other conditions. The tremendous energy of the percussive wave in an underwater explosion is evidenced by the immediate upheaval of the water when the explosion occurs. The geyser-like eruption which occurs shortly afterwards is caused by the rise of the gases of the explosion to the surface.
2B7. The explosive train
Modern explosive devices, even of simple types, very rarely contain one explosive or explosive component only. They commonly apply the principle of chain reaction, in which a chain or train of elements functions in sequence. The first part of the train, called the initiator, primer, cap, or detonator, begins the action when set off by an electric current, shock, heat, friction, or some other stimulation. The heat or shock of explosion of this first part of the train sets off one or more succeeding parts in sequence. Depending on their functioning, these are called ignition, booster, or auxiliary charges. The final link in this intermediate sequence (which may consist of one or more such links) ignites or detonates the main (burster, disrupter, or propellent) charge.
There are two main types of explosive train, depending on the purpose and nature of the main charge. Propelling or impulse charges are low explosives intended to develop, through rapid burning, energy to be used for propulsion. An explosive train for a propelling charge generally begins with a primer which produces a hot flame. This sets off the ignition charge (composed of a flame-producing explosive-black powder) Last in the explosive train is the propellent powder or grain itself, which burns to produce the hot high-pressure gases which propel the gun projectile or rocket.
In the explosive train designed to detonate a high explosive, the sequence of operation in general depends on the transmission and amplification of shock rather than a hot flame. The initiating device contains a sensitive explosive which produces shock when set off; the initiating shock sets off the booster or a series of boosters or auxiliaries; the magnified shock detonates the main charge. The booster may be composed of the same explosive as the main charge, but in more sensitive form. Thus, granulated TNT, which is more sensitive than the cast variety, is used as a booster in depth charges.
2B8. Classification of explosives according to service use
Naval explosives may be classified according to the use to which they are put:
1. Propellants and impulse explosives. These explosives are used to propel projectiles from guns, to propel rockets, launch torpedoes, launch depth charges from projectors, and catapult aircraft. They are all burning or low explosives. Examples are smokeless powder, ballistite, Cordite, and black powder. Figure 2B1 shows smokeless powder grains of various sizes.
|2. Disrupting explosives. Explosives of this classification are all employed to create damage to the target under attack. They are all of the high explosive type and are used alone or as part of the explosive charge in mines, bombs, depth charges, and torpedo warheads, and in projectiles as a burster charge. There is a wide variety in this category, but the more common examples arc RDX, TNT, ammonium picrate, and tetryl.
3. Initiating (primary) explosives. As explained in article 2B6, the initiation of an explosive reaction requires the application of energy in some form. Propellants are commonly ignited by the application of flame, while disrupting explosives are set off by a severe shock. Many primary explosives can be used for initiating either propellants or disrupting explosives, because they produce both a flame and a shock when exploded.
The device used to initiate the burning of a propellent explosive is called a primer. A simple primer consists of a small amount of lead azide and a small charge of black powder in a container. When fired, the primer produces the long, hot flame required to ignite the propellant.
The device used to initiate the reaction of a disrupting explosive is called a detonator, and in most cases it consists of a charge of lead azide or lead styphnate either alone or with granular TNT or tetryl in a container. When fired, the detonator produces the shock necessary to initiate the explosive reaction.
4. Auxiliary explosives. Large propellent charges and relatively insensitive disrupting explosives require an intermediate charge, so that the flame or shock of the initiating explosive may be increased to ensure proper reaction of the main explosive charge. The intermediate or auxiliary explosive used with propellants is called an ignition charge and consists of a quantity of flame-producing black powder sufficient to engulf the propellent grains. The auxiliary explosive used with disrupting explosives is called a booster and consists of a quantity of more sensitive high explosive, such as tetryl or granular TNT. The booster increases the shock of the detonator to a degree sufficient to explode the disruptive charge.
| C. Service Explosives; Propellants
The primary function of a propellant is to provide pressure which, acting against the object to be propelled. will accelerate the object to the required velocity. This pressure must be so controlled that it will never exceed the strength of the container in which it is produced (e. g., guns, torpedo tubes, and depth charge projectors). The control of pressure produced by propellants and impulse charges is treated in considerable detail in the chapter on interior ballistics.
It would be possible to use any explosive for propellent purposes if the velocity of explosion could be controlled. Investigations of this problem led to the development of smokeless powder as we know it today. Nitrated cotton, the main constituent of smokeless powder, is a high explosive by itself and entirely unsuitable as a projectile propellant. However, it was discovered that this high explosive could be colloided with an ether-alcohol mixture to produce a “burning” explosive. Only a small number of chemical compounds can be so treated as to permit control of the velocity of explosion. Furthermore, the substance in its final state must not only be efficient, but must be safe in use, easy to handle, and stable under varying conditions of storage for protracted periods of time.
Smokeless powders of one form or another are now used almost universally for propellent charges. For military purposes (especially for guns larger than small arms) they may be considered to be of two classes: (1) single-base powders, and (2) multi- (double or triple) base powders.
In the single-base powders, cellulose nitrates (referred to hereafter as nitrocellulose) form the only explosive ingredient. The other materials present in single-base powders are included to obtain suitable form, desired burning characteristics, and stability.
In the double- or triple-base powders, nitroglycerin is present to assist in dissolving the nitrocellulose during manufacture, as well as to add to the explosive qualities. The single-base nitrocellulose powders produce a greater volume of gas, but less heat than the double-base powders. From a thermodynamic standpoint, single-base nitrocellulose powders are somewhat less efficient, because of their lower burning temperatures. But they have the advantage of causing less wear in the gun bore than double-base powders do. Present triple-base powders, however, have a large proportion of the “cool”-burning explosive nitroguanidine; they therefore produce maximum temperatures comparable to those of single-base powders. Triple-base powders also have other advantages, which are mentioned in article 2C5.
2C2. Smokeless powder manufacture
The smokeless powder used by the United States Navy is a uniform ether-alcohol colloid of carefully purified nitrocellulose to which is added a small quantity of diphenylamine to assist in preserving the chemical stability of the powder. The principal raw materials used in the manufacture of United States Navy smokeless powder are:
1. Cotton. The cellulose material to be nitrated consists of bleached and purified short-fibered cotton, which is 90 percent pure cellulose.
2. Acids. A mixture of about 1 part nitric acid to 3 of sulphuric acid by weight is used in the nitrating process.
3. Ether and alcohol. A mixture of ethyl ether and ethyl alcohol is used as a solvent for the nitrocellulose.
4. Diphenylamine. This substance, used as a stabilizer, has a slightly alkaline reaction and is incorporated in the powder to neutralize any acid products which might be formed as a result of gradual decomposition of the powder. Since it thus prevents decomposition from becoming progressive, it adds to the stability of the powder.
The principal steps in the manufacture of United States Navy smokeless powder are as follows:
1. Preparing the cellulose. The purified cotton is passed through picking machines which tear apart the knots and tangles, and then through driers which reduce the moisture content to about 1 percent, moisture being undesirable in the nitrating process.
2. Nitrating. The cotton and acids are thoroughly mixed and agitated in nitrators. The cotton is converted into nitrocellulose containing about 12.6 percent nitrogen. This is commonly called “pyro.” After nitrating, the pyro and excess acids are sent to a centrifugal wringer below the nitrator, where the spent acids are removed.
3. Purifying. The pyro is immersed in water and run through flumes to boiling tubs where it is given a preliminary boiling for about 40 hours to remove the remaining free acids. It is then transferred to pulpers which cut and grind it to the desired consistency. The pyro is then boiled in water in poaching tubs for 12 hours, during which time the water is changed at regular intervals.
4. Dehydrating. After the final stage of purification in the poaching tubs, the pyro is transferred to the dewaterers (large rotary filters equipped with wet vacuum pumps) and to centrifugal wringers which remove water. The remainder of the water is forced out by placing the pyro in the cylinder of a hydraulic press and forcing alcohol under pressure through it. The pyro cake formed is subjected to a final pressure treatment to remove excess alcohol, leaving only sufficient alcohol for making the desired colloid.
5. Mixing. The compressed pyro cake is now placed in rotating drums and block breakers and broken up into a coarse, fluffy mass. It is then put into mixing machines where ether and diphenylamine are added. The charge is mixed for about 30 minutes, during which it becomes partially dissolved or colloided by the ether and alcohol.
6. Granulation. After mixing, the charge is reformed into a block and taken to a press where it is first forced through the small holes of a strainer (macaroni) press to ensure a thoroughly mixed and uniform colloid and to eliminate lumps and foreign matter. It is again reblocked and taken to a graining press, where it is forced through the die and extruded in the form of a continuous cord of circular cross section with seven longitudinal perforations. The cord immediately passes to the grain cutter, which cuts it into grains of uniform length. In this form, it is known as “green” powder and is still fairly soft and pliable because of the excess of solvents which it contains.
7. Drying. After a special heat treatment for recovery of most of the solvents, the green powder is removed to large dry houses, where the solvent content is reduced to a predetermined amount. The drying process takes 4 to 6 months, depending on the percentage of residual volatiles desired and the size of the grain required. The percentage of residual volatiles remaining in each powder after drying varies from 3 to 7 percent, being greater in the larger granulations. After drying, the powder is blended with other poacher lots to make up one uniform lot of powder. Samples of this lot are proof-fired, and after acceptance the lot is assigned an index number. It is then ready for issue to the Fleet.
2C3. Characteristics of smokeless powder
Grains of smokeless powder have a hard, smooth finish and look very much like corn. When new, the grains are amber in color and are translucent. As the powder ages, its color becomes dark brown, then black, and finally opaque. These changes do not indicate any loss of stability.
Smokeless powder is subject to a very gradual chemical decomposition which may in time be a source of danger (spontaneous combustion) unless measures are taken to arrest such action. Like many explosive compounds, smokeless powder is in a state of unstable chemical equilibrium and is readily acted upon unfavorably by impurities which may be present with it. If decomposition takes place in any particle, the decomposition products will include nitrogen oxides which have an acid reaction and will facilitate further decomposition. The use of diphenylamine, whose action has already been explained, has greatly increased the stability life of smokeless powder. A powder which may have become chemically dangerous through partial decomposition is not dangerous for use in a gun, since a part of the decomposition which should take place in the gun, with sudden evolution of heated gases, has already taken place and the powder has lost a corresponding number of heat units.
Excessive heat has a most unfavorable influence upon the stability of smokeless powder. At temperatures below 60 degrees F., the stability is not appreciably affected, but at temperatures above 70 degrees F., the rate of decomposition rises quickly, becoming high at 90 degrees F., and dangerously accelerated at temperatures over 100 degrees F. Precautions must therefore be taken to ensure the maintenance of a uniformly low temperature in the magazines in which powder is kept.
Since the presence of moisture favors decomposition of smokeless powder, the containers in which it is stored are made airtight, and every effort must be made to maintain their tightness. A leaky container may not only admit undesirable moist air to the powder, but may also permit the loss of volatiles through evaporation, especially if the air in the container is subjected to alternate expansion and contraction due to change in temperature. Such a loss of volatiles will increase the speed of burning of the powder to such an extent that excessive pressures will be produced in the gun. In this event the powder is ballistically dangerous.
2C4. Triple-base powder manufacture
Triple-base powder, commonly called Cordite N or SPCG, is composed of four principal ingredients- nitrocellulose (19 percent), nitroglycerine (a little under 19 percent), nitroguanidine (55 percent), and ethyl centralite (a little over 7 percent). Of these 4, the first 3 are explosives. Ethyl centralite (also called carbamite) is the stabilizer. A small amount of potassium sulfate may be added as a flash inhibitor, and for some calibers other ingredients may be added in small amounts.
The manufacturing process is in general similar to that for pyro powder. It begins with passing the dehydrated nitrocellulose through a block-breaker screen (or this may be done before the nitrocellulose reaches the Cordite production plant). Then the other dry ingredients (except the ethyl centralite) are mixed with the nitrocellulose for 6 minutes. Next, a mixture of nitroglycerine and acetone (which desensitizes the normally very touchy nitroglycerine) is added to the dry mix, and mixing continues for another half hour. Then the ethyl centralite is added and mixing goes on for another 3 hours. More acetone and alcohol may be added if required during this step. This stage may end with maceration of the mix, if required.
The mix, which is by now mostly in colloid form, next goes to a “macaroni” press which squeezes it through strainers to remove uncolloided nitrocellulose and bits of foreign matter that may be present. The “macaroni” is then pressed again into blocks, and is extruded through dies to give the final grain cross section. After this the extrusions are cut to proper grain length, and the powder goes to the final stages of its processing.
The “green” powder next goes through a combined screening-drying stage, in which clustered grains are separated, undersize grains and dust are screened out, and forced dry-air currents remove volatiles. After drying, the powder is blended with other lots and packed.
2C5. Characteristics of triple-base powder
Triple-base (Cordite) powder grains resemble in size and shape conventional pyro powder grains for the same caliber, except that they have smooth, chalk-white surfaces. After considerable time in storage, the surface color may tend to yellow, but this is not a sign of deterioration.
Triple-base powders are far more stable in storage than equivalent pyro powder, partly because of their relatively low nitrocellulose content, partly because of their extremely small content of volatile components, and partly because of their low hygroscopicity. They are much more suitable as gun propellants than double-base powders like ballistite (described below) because nitroguanidine, in contrast to the mixture of nitroglycerine and nitrocellulose in double-base powders, is a “cool”-burning explosive. The gases produced by a triple-base powder with nitroguanidine have much less erosive effect than those of a double-base powder. Triple-base powders also have advantages in reduced production cost and reduced residue after burning, although they do in general require a larger variety of ingredients than pyro powder. They are also less sensitive to high temperatures in stowage.