Chapter XII: Explosives, Ammunition and Fuses

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EXPLOSIVES.

As a matter of practical interest, explosives may be divided into three classes, namely:

(1) Progressive or =propelling explosives= called =low explosives=.

(2) Detonating or =disruptive explosives=, termed =high explosives=.

(3) =Detonators= or exploders, known as =fulminates=.

The first includes all classes of gun powders used in firearms of all kinds; the second, explosives used in shell, torpedoes, and for demolitions; the third, those explosives used to originate explosive reactions in the two first classes. Corresponding names are given to the phenomena characteristic of each class of explosives, (1) explosions proper, of low order, progressive, or combustions, (2) detonations, of high order, (3) fulminations, this last possessing exceptional brusqueness.

The explosion of low order is marked by more or less progression; the time element is involved as a controlling factor, the time required to complete the explosive reaction being large compared with that of the other forms of explosion.

The second class of explosion is of a different nature. The explosive reaction is not limited or confined to the surfaces exposed but appears to progress in all directions throughout the mass radially from the point of initial explosion. It has been determined experimentally that the velocity of propagation of the explosive wave throughout a mass of guncotton is from 17,000 to 21,000 feet per second.

Fulmination is a class of explosion still more brusque than the last. The abruptness of their explosion and the consequent sharpness of the blow and the concentration of heat on the point of ignition constituting their efficiency as originators of explosions of the first two classes.

=Methods of Exploding.= Explosives may be exploded by three methods; in reality but two, by heat and by application of energy as by a blow. The heat may be applied directly by friction, by electricity and detonating cap, these two methods of applying the heat giving rise to the three practical methods above mentioned. As it is not practical to apply heat directly to the charge, small charges of special explosives are made up into primers and these are exploded in one of the ways above mentioned and so communicate the explosion to the main charge. Fulminate of mercury is one of the high explosives fulfilling the requirements and it is readily exploded by any one of the methods mentioned. It is used in all detonating caps. Primers for cannon also contain an additional charge of black powder to increase the flame. For this purpose also igniting charges of black powder are attached to the smokeless powder charges for the larger calibers.

=Uses.= The chief use of low or progressive explosives is as a propelling charge in guns and for blasting where it is desired to exert a pushing effect rather than a blow. High explosives are used when it is desired to exert a high pressure and shatter the container, as in a shell, mine, etc. This class is not satisfactory as a propelling charge for the reason that its rapidity of action is so great that the pressure exerted would burst the gun before the projectile could start. Low explosives are not satisfactory shell fillers for the reason that their action is so low that the shell would break at its weakest point before all the explosives had exploded and what remained would be wasted. With a high explosive, all or most of the charge explodes before the shell can break up. The greater the rapidity of action of an explosive the finer the fragmentation of the projectile. With too rapid action the pieces are too small; with too slow action they are too large. Experience teaches the proper rapidity of action to attain the fragmentation most efficient against animate and material targets.

=Propelling Charges.= Up to the present time nitrocellulose powder has complied better with the requirements of a suitable, smokeless powder than any other that has been proposed and is used in our service for propelling charges in guns. The danger of manufacture is also less than that of nitroglycerine powders. Moreover the latter, which was formerly used in our service and still is in the British and some others, causes too much erosion of the tubes due to the greater heat of explosion. It has the advantage of requiring a smaller charge for the same muzzle velocity and therefore a smaller powder space and consequent lighter weight of gun.

=Shell Fillers.= High explosives for shell fillers. Up to the present explosive “D,” trinitrotoluol and picric acid are the principal high explosives which fulfill the requirements as shell fillers. Explosive “D” on account of its great insensitiveness to shock is used in armor piercing projectiles and also in field gun and howitzer shell. It is detonated by a fuze. Trinitrotoluol is used in submarine mines and in general demolition work as it is much easier to explode than explosive “D.”

=Table of Explosives.= The following table gives a good idea of the principal explosives in use in our service and the characteristics of each:

High
Purpose. or Low. Name.
Propelling charge in guns. L Nitrocellulose, smokeless
powder.
Bursting charge, projectiles. H Picric acid, explosive “D”
(powder form)
Trinitrotoluol.
Blank, saluting charges. L Black Powder.
Re-inforce charges, primers. L Black Powder.
Base charge, shrapnel. L Black Powder.
Time trains, fuzes. L Black Powder.
Igniting charges, cannon. L Black Powder.
Charges, submarine mines. H Trinitrotoluol wet guncotton.
Igniting elements, fuzes H Fulminate of mercury, chlorate
and primers. of potash (potassium
chlorate).

=High Explosives.= The principal high explosives used as shell fillers in our service are: picric acid, explosive “D” and trinitrotoluol, or more popularly known at TNT. The picric acid and picrates used as shell fillers are secret compositions. Mellinite, essentially picric acid alone or with some other substance is used as a shell filler by the French. It is poured into the shell in a fused state and allowed to harden, thus giving a very compact charge and one easily handled. It has the disadvantage however of forming unstable compounds with the metal of the shell and great care must be exercised in coating the interior of the shell with a protective coat before pouring in the fused mellinite. Lyddite is the English equivalent of mellinite. Picric acid was also used by the Japanese or it may be a mixture of picric acid and some nitro compound. The most successful explosive of this type is explosive “D” invented by Colonel Dunn of our Ordnance Department and sometimes known as “Dunnite.” It is not fusible and must be compressed for use as a shell filler, being forced into the shell by compression. This is a disadvantage as compared to mellinite as the density of loading is less and weight for weight therefore less efficient. It is little sensitive to shock and therefore not very dangerous to load even under great pressure. Trinitrotoluol is also used as a shell filler but its chief use is in demolition work and as the charge for submarine mines.

=Nitrogen Compounds.= It may be interesting to note that all of the principal explosives with which we have been dealing are compounds containing nitrogen. In fact the war has been fought with fixed nitrogen which explains the great interest taken in the various attempts to fix the free nitrogen of the air which is the world’s great storehouse of free nitrogen. As nitrogen is also a necessary ingredient in the various fertilizers, the result to the world of a commercial process for speeding up the cycle of changes through which nitrogen passes in its life giving mission from free nitrogen in the air to its various compounds in the nitrogeneous animal and vegetable tissues is almost limitless and as usual war has been the incentive to speed up a process which will result in incalculable value to mankind.

=Classification.= Guns are loaded with three kinds of ammunition: fixed, semi-fixed and separate loading ammunition. In fixed ammunition the round is complete and projectile and powder loaded into the chamber at the same time. In semi-fixed the projectile is separate from the powder charge, which however is put up and loaded into the chamber in a container. In separate loading ammunition the powder is loaded into the chamber in bags. In the first two cases the cartridge case furnishes the means for sealing the rear of the powder chamber against escape to the rear of the powder gases. In the last case some form of obturating device is made a part of the breechblock furnishing a gas check to seal the rear of the powder chamber.

=Fixed Ammunition.= All of our field guns below 5 inches in calibre use fixed ammunition. The powder is placed loose in the cartridge case, the space not filled with powder being stuffed with packing paper, excelsior, or felt wadding next to the projectile so as to hold the powder in contact with the primer, in some fixed ammunition a brass diaphragm is soldered to the inside of the case for the same purpose and to keep out moisture, (4.7” Gun). An igniting charge of black powder is a part of the primer and in some cases an additional charge is placed at the forward end of the powder space in the cartridge case to insure rapid ignition of the smokeless powder. In this case it is held in place between two quilted disks of crinoline.

=Semi-fixed ammunition= is employed in our 6” and 4.7” field howitzers. The cartridge case contains three weights of propelling charge for firing in the three zones designed to give a high angle of all with these weapons. Access to the charge is had by tearing off the brass diaphragm closing the forward end of the cartridge case. By removing the first charge the remaining charge is that prescribed for the second zone, and by removing the top two charges the remaining charge is that of the first zone. The three charges are tied together and the middle charge has an igniting charge of black powder attached. The removal of charges is facilitated by the separate container for the powder charge and the round is more easily handled in the two parts especially in the case of the six-inch howitzer, where the projectile weighs 120 lbs. The same primer is used as in fixed ammunition, the cartridge case performing the function of an obturator.

=Separate Ammunition.—Obturation.= The 155-mm Filloux gun and 155-mm howitzer use separate ammunition. In such guns there must be provided some form of a gas check which will prevent the powder gases from rushing to the rear into the threaded portion of the breechblock, as this would soon erode the thread sectors and render the gun useless beside losing a large amount of pressure in the bore. The device used as a gas check is called an obturator. There are two systems of obturation in use, named after their inventors:

The DeBange and the Freyre. The former is used in the 155’s. It consists of a steel mushroom head closing the rear of the powder chamber, the spindle of which passes through a central hole in the breechblock. Between the mushroom head and the face of the breechblock is a pad of asbestos, paraffine and tallow, pressed into shape by a hydraulic press and covered by canvas or asbestos wirecloth. Split rings having hardened outer surfaces are fitted, one just behind the mushroom head and one just in front of the face of the breechblock. Their diameter is slightly greater in the free state than the conical surface of the bore where they bear when the breech is closed so that they always close the rear of the powder chamber. The pressure of the powder gases forces the mushroom head to the rear and this compresses the asbestos pad which in turn forces the split rings to bear with greater force against the walls of the powder chamber thus securely closing the rear opening of the powder chamber. For more details of this device see pages 302 to 306 Tschappat’s O & G.

=Powder Bags.= Cartridge bags for separate loading are made of raw silk, and are sewed with silk thread. Other materials are apt to produce flare-backs or premature explosions because they are not entirely consumed in the bore or continue to burn if not consumed. The raw silk however either is entirely consumed or if not, the parts ignited immediately go out as soon as the flame is removed and do not smoulder. Specially treated cotton fibre bags have been tried but so far as I know have not as yet superseded the raw silk for the purpose. The gases remaining in the bore after the discharge of a charge of smokeless powder are explosive and with air form an explosive mixture, hence the danger upon opening the breech if any smouldering particles remain in the bore.

=Primers.= The devices for initiating explosions of propelling charges in military guns are called primers. With fixed and semi-fixed ammunition the primers are seated in the base of the cartridge case. In the case of separate loading ammunition the primers are inserted separately in the breechblock, the expanding gases of the detonated primer forcing the walls of the primer case tightly against the bore through the breechblock and thus sealing this channel of escape for the gases from the powder chamber. This necessitates a much larger and stronger case for separate loading primers than for those inserted in the base of a cartridge case.

=Classes of primers.= Primers are divided into three classes according to the method by which they are fired: (a) _friction primers_, (2) _electric primers_, (3) _percussion primers_. Combination primers are made which may be fired by any two of these methods, usually electric and one of the others. The characteristics of a good primer are, certainty of action, safety in handling, no deterioration in storage, simplicity in construction and be cheap to manufacture. They are also divided into obturating and non-obturating depending upon whether they close the vent during discharge or not.

=Primer pressing.= Primers for fixed ammunition are inserted in the base of the cartridge cases by means of a special press for this purpose. The primer body is a trifle larger than the seat in the cartridge case provided. This seat is rough bored to a diameter less than the finished size and then mandreled to finished dimensions with a steel tapered plug. This process toughens the material of the case around the primer seat and prevents the expansion of the primer seat under pressure of the expanding gases.

=Percussion primers.= Except for very heavy siege guns and railroad artillery the guns handled by the Field Artillery use percussion primers. The 110-grain percussion primer is the one in use in our service and as typical will be described. The charge consisting of 110 grains of compressed black powder makes the charge burn like a torch rather than explode, which facilitates the ignition of the charge of smokeless powder, with which the flame comes in contact. The diametral holes spray the flame in several directions thus insuring ignition at many points simultaneously. The percussion element consists of a percussion primer cup, the percussion composition and an anvil, all of which are assembled together in a cup in the rear face of the primer case. The percussion composition is made up of chlorate of potash, sulphide of antimony, ground glass and sulphur. A blow upon the cap by the firing pin detonates the percussion composition and the flame from this detonation ignites the black powder which in turn explodes the charge of smokeless powder.

The General Shape and Nomenclature of Projectiles.

The reason for the particular shape of shells may not be clear to all. In the first place all matter has the property known as inertia, which we may define as that tendency of matter to remain in a state of rest or to continue at a uniform velocity if in motion. It offers a resistance to any change in the state of either rest or motion whether of amount or direction. Consequently when we apply a sudden and tremendous force to the base of a projectile by means of the expansive force of exploding powder gases, there will be set up in the metal a resistance to this force in which every particle of the projectile will resist by an amount proportional to the mass of particles beyond the point of application of the force to itself. The actual force will be proportional to the weight and acceleration produced by the applied force in the projectile. This explains the reason why the _walls of the projectile are thicker near the base_. It also explains the method of calculating the thickness of walls, for if we know the weight at any cross section and the co-efficient of strength of the metal we may calculate the thickness of walls necessary to withstand the pressure for any given muzzle velocity which is fixed by other considerations. It explains also the preference for steel in projectiles as for the same weight the steel is much stronger making it possible to throw a greater amount of shrapnel or high explosives in shell.

The necessity for compact loading, especially in the case of high explosive shell is also noted as otherwise the shock due to inertia would break up the charge and perhaps cause a premature explosion. Hence it is very necessary to guard against airholes in filling shell cavities.

In order to secure regular and uninterrupted movement of the projectile through the bore it is necessary that the projectile and bore have the same geometric axis. Also the projectile must be seated exactly and uniformly for succeeding rounds in its seating in the bore. This latter is necessary in order that the powder chamber may not vary as this would give irregular pressures. The liability of _strapping the rotating bands_ or setting off the fuze in certain kinds of fuzes are also explained by inertia. It might even cause sufficient shock to detonate the charge in the shell. The remedy is accurate seating of each projectile by reason of trained gun crews using the same amount of force at each ramming. The first condition, coincidence of axes, is obtained by means of the ogival head which has a diameter some tenths of a millimeter smaller than the diameter of the bore, and serves as a front support for the projectile while the rotating bands center it in rear. Were it not for the bell the projectile, held only by the soft material of the rotating band, would wabble in its travel through the bore and tumble soon after leaving it. It is also necessary that the center of gravity of the projectile be on its geometric axis. Otherwise it will travel on a spiral of the same pitch as the grooves and knock the tube walls as it travels through the bore and without the support of the bell might cause a premature explosion by actuating the fuze.

COMMON STEEL SHELL MODEL OF 1905.

SHRAPNEL.

CARTRIDGE CASE.

4.7” Gun Ammunition.]

Three-inch Ammunition.

=Fixed ammunition= is used in the 3” field guns, and is made up with either common shrapnel, high explosive shrapnel, or common steel shell. The rounds as made up vary in length with the type of projectile used. The ammunition chests of the battery are of sufficient size to take any one of the rounds furnished, so that the number of each kind to be carried is a matter for regulation by proper authority. Each round is issued with projectile filled and fused. The weight of the projectile is 15 pounds, and the total weight of one round is 18.75 pounds. The components of one round are _the cartridge case with primer, the powder charge, igniter, projectile and fuze_.

=The cartridge case.=—The cartridge case is a solid drawn-brass case 10.8 inches long; it has a capacity of 66.5 cubic inches, and weighs, with primer, 2.25 pounds. A circular groove is cut in the base of the cartridge case and _the groove is painted red for high explosive shrapnel, yellow for common shrapnel, and black for high explosive shell_.

=The primer.=—The percussion primer, known as the “110-grain percussion primer,” contains an igniting charge of 110 grains of black powder in addition to the essential elements of a percussion primer. The purpose of the black powder is to insure the ignition of the smokeless powder charge in cartridge case.

_Common Shrapnel._

_Cartridge Case._

_Semple Tracer._

_High Explosive Shrapnel._

3” AMMUNITION]

=The powder charge.=—The powder is a nitrocellulose powder composed of multiperforated (7 perforations) cylindrical grains, each 0.35” long and 0.195” in diameter. The charge varies slightly for different lots of powder, but is approximately 24 ounces. The charge gives a muzzle velocity for shrapnel of 1,700 feet per second (1600 f/s for shell) with a maximum pressure in the bore not exceeding 33,000 pounds per square inch. At the front end of the cartridge case there is an igniter of black powder weighing about ¼ oz. which assists in the uniform ignition of the smokeless powder charge.

=The projectiles.=—All projectiles have a copper rotating band 1.2” from the base. This band engages in the rifling of the bore of the piece, and gives the projectile a rapid rotation about its long axis during flight. This causes it to travel straight, point on, without tumbling.

=Common shrapnel.=—The common shrapnel is a base-charged shrapnel fitted with a combination fuze. The case is of steel with solid base. The shrapnel filling is composed of 252 balls, each approximately 167 grains in weight (42 to the pound). The balls are approximately 0.5” in diameter. The balls are poured around a central tube and rest upon a steel diaphragm, the interstices containing a smoke-producing matrix. The bursting charge consisting of 2¾ oz. of black powder is in the base and is covered by the diaphragm which supports the central tube, affording a conduit to the flame leading from the fuze to the bursting charge.

In action the case is not ruptured upon the explosion of the bursting charge; the head is stripped and the balls are shot out of the case with an increase of velocity of about 274 feet per second. The remaining velocity of the shrapnel at 6,500 yards is approximately 724 feet per second and the time of flight 22 seconds, so that at that extreme range, with the increase of velocity due to the bursting charge, this shrapnel with 21-second fuze will be effective. The weight of the shrapnel with fuze is 15 pounds.

Shrapnel is a projectile containing a great number of hardened steel balls, each approximately ½” diameter, which may be projected from a point in the air (called the _point of burst_) close to but short of the target. Each ball is capable of killing a man or horse at a distance up to 250 or 300 yards from the point of burst. Taken collectively, the paths of these balls form a cone, called the _cone of dispersion_. The ground section of this cone is elliptical in shape with its longer axis approximately in the plane of fire. At mid-range when burst at _normal height of burst_ (H. B. = 3 mils), the dimensions of this area are approximately 20 yards wide by 250 yards deep. These dimensions will however vary with the _angle of fall_, _the height of burst_, the _slope of the ground_ at the target, and the relation between the _linear_ and the _rotational velocities_ of the shrapnel at instant of burst in the air. A 3-mil H. B. is chosen because this gives an average density of 1 hit per square yard of vertical target area. An infantry skirmisher (standing) with his interval occupies approximately 1 square yard.

Shrapnel has very little effect upon material objects. It is very effective against personnel not protected by cover, or to search an area which is known to be occupied, or which must be traversed, by hostile troops.

_Ehrhardt High-explosive shrapnel._—The Ehrhardt high-explosive shrapnel is fitted with a combination fuze and a high explosive head. The case is drawn steel with solid base. The shrapnel filling is composed of 285 balls, each approximately 138 grains in weight (50 to the pound). The balls are poured around the central tube and rest upon the steel diaphragm, the interstices containing a matrix of high explosive.

In time action (burst in air), the case is not ruptured upon the explosion of the bursting charge, but the head is forced out and the balls are shot out of the case with an increase of velocity of from 250 to 300 feet per second. In the meantime the head continues its flight, detonating on impact.

If the fuze be set at “safety” or for a time greater than the actual time of flight, this shrapnel may be used in lieu of high-explosive shell. Upon impact a high-explosive shrapnel is detonated by means of the percussion element of the combination fuze, the head being detonated first, which detonation causes the sympathetic detonation of high-explosive matrix surrounding the balls.

=Common steel shell.=—This steel shell is high-explosive and fitted with a base detonating fuze. The case is hollow and made of drawn steel. It is provided with an ogival head. The steel shell contains a bursting charge of 13.12 ounces of Explosive D. The weight of the shell with bursting charge and fuze is 15 pounds. The shell is always issued filled and fuzed.

This shell bursts on impact and with great force exerted in all directions. It is a powerful instrument for the destruction of material objects such as guns, intrenchments, houses, stone walls, etc. The effect, however, is very local.

=Frankford Arsenal combination fuzes.=—These fuzes are point fuzes with combination time and percussion elements for use with common shrapnel. They are of the type known as the ring or “dial” fuze, in which the time train is set by turning a graduated ring which carries part of the train. These fuzes may be reset as often as desired.

=Ehrhardt combination fuze for high explosive shrapnel.=—This fuze is similar to the Frankford Arsenal Combination time and percussion fuze but in addition contains a high explosive head and detonating element. Due to this arrangement, both the projectile and the high explosive head have a high-explosive shell effect when striking on impact.

=The service base detonating fuze.=—The details of the detonating fuze and the composition of the detonator are kept secret. A detonating fuze is necessary in order to produce a higher order of explosion by causing an instantaneous conversion of the high explosive compound called “Explosive D” with which the shell is charged. If an ordinary percussion fuze were used only an ordinary explosion would be produced as in the explosion of black powder.

=Preparation of blank metallic ammunition.=—Blank metallic ammunition will always be assembled under the personal supervision of a commissioned officer, who will be held responsible that it is prepared in the manner prescribed. (G. O. 9, War Dept., Jan. 11, 1908.)

For this purpose there are issued blank-cartridge cases, black powder in bulk, tight-fitting felt wads, rubberine, or other quick-drying paint, primers, etc.

Before assembling, the cartridge cases should be carefully inspected to see that they are in sound condition and thoroughly clean and dry. They should also be tested by trying them in the gun, to determine whether they have become deformed. Any cases that do not readily enter the chamber in the gun or that are otherwise seriously deformed should be laid aside for resizing. After inspecting the cartridge cases the blank ammunition should be prepared as follows:

(a) Insert the primers with the primer-inserting press.

(b) Pour into the cartridge case the proper weight of black powder and shake it down well.

(d) Give the upper surface of the felt wad and the inside of the cartridge case just above the wad a good coat of the rubberine or other quick-drying paint furnished for the purpose, using a brush, and allow the case to stand until this coat is dry. Then apply another coat of rubberine paint in a similar manner. The object of using rubberine paint, which is strongly adhesive, is to thoroughly seal the joint between the wad and the case to prevent any powder grains from leaking out, and at the same time to firmly hold the wad in place.

=The reloading and cleaning outfit.=—This outfit consists of the following parts, and is furnished to each battery:

Primer-inserting press, small
Bushing
Powder measure, saluting
Decapping tool, with guide
Cleaning brush
Hammer
Case holder
Case-holder stand
Storage chest

The bushing is used in the primer-inserting press for the insertion of new primers.

The decapping tool and case holder and stand are used for removing exploded primers from the cartridge cases. A light blow on the rod with a piece of wood or the bronze hammer generally removes the primer.

A powder measure to suit the saluting charge for the gun is furnished, and when level full holds the required charge.

The cleaning brush is furnished for cleaning the cartridge cases after they have been used and should be ordered to suit the size of case for which intended.

=Care of Cartridge Cases.=—As soon after firing as practicable the exploded primers should be removed from the cartridge case by means of the decapping tools furnished with the reloading outfit. The case should then be thoroughly washed in a strong solution of soft soap and soda to remove all powder residue. It should then be thoroughly dried.

If the cartridge cases are carefully cleaned and washed immediately after firing, not only will less labor be required but the life of the cartridge case will be greatly prolonged.

A good solution for washing cartridge cases may be prepared by using ingredients in the following proportions: 1 gallon of water, 2½ ounces of soft soap, 5½ ounces soda. The mixture should be boiled and stirred until the ingredients are entirely dissolved.

In washing cartridge cases this solution should be used hot and in sufficient quantity to completely immerse the cases.

Neither acids nor solutions of acids will be used for cleaning cartridge cases.

Precautions to be Observed with Fixed Ammunition.

(a) Do not unnecessarily expose ammunition to the sun or load it into a warm gun before time for firing; if this is done, erratic shooting will result.

(b) Handle carefully, otherwise cartridges may become deformed and cause jams.

(d) See that fuzes set at safety or are provided with waterproof brass cover for transport.

(e) Do not fire ammunition which has been under water with the waterproof brass cover removed.

(f) Both service and blank ammunition should never be carried in the battery at the same time. If conditions are such that both may be used in exercises, only one kind should be in the firing battery; the other should be under lock and key outside the firing position.

(g) Misfires and hangfires are of exceedingly rare occurrence. In case of a failure to fire, the firing handle should be pulled again in order to snap the trigger. If this fails to fire, the breech should _not be opened_ until after the expiration of at least one minute, when the round or cartridge should be removed and placed to one side. Defective ammunition, cartridges and primers should be reported.

With Blank Ammunition.

Firing with blank ammunition will be greatly facilitated by a careful observance of the following:

(a) Before firing, a careful examination should be made of the assembled rounds to see that the felt wads have not become displaced or the cartridge cases dented or deformed by careless handling. If the cartridge cases have been properly resized and are clean, no difficulty should be experienced in inserting them in the gun, provided the chamber of the latter is clean. The continued insertion of cartridge cases that are not clean causes an accumulation in the gun chamber which may make the insertion of subsequent rounds difficult or impossible.

(b) In firing blank ammunition the gun chamber will be sponged after each round with a damp sponge, to extinguish sparks and remove powder residue resulting from the previous round, before the insertion of another round.

(c) Care will be taken to see that the sponges are not worn and that they thoroughly fit the chamber. The interval between rounds in firing blank ammunition should be sufficient to allow thorough sponging of the chamber and examination to ascertain that all sparks have been extinguished.

(d) Wads for the preparation of blank metallic ammunition are made to tightly fit in the cartridge case. No wads should be used that are not a tight fit in the case.

FUZES.

=Principle of operation.=—We have just learned something of the force of inertia in connection with a projectile. Most fuzes are actuated by this force. From our knowledge of the trajectory we know that usually a projectile does not strike on its nose. Therefore we cannot devise our fuzes to work like the driving of a nail into a board. The striking element is the anvil and is a fixed pointed spur against which a sliding element containing a fulminate strikes. The sliding block carries a small charge of black powder which is set off by the fulminate, thus igniting the train which leads to the high explosive charge detonator. Were this sliding block left free to slide back and forth at all times it would be unsafe to transport the fuze, as it might be set off by accident. There must be therefore some means of holding it safely away from the anvil until it is desired to detonate the charge. There are thus two conflicting conditions to be met: safety during transportation and sensitiveness at the point of departure. It may not be understood at first why sensitiveness at the point of departure should be a condition to be met. Suffice it to say that all fuzes are designed to arm at discharge or soon after leaving the bore for they must be ready to act at any time after leaving the muzzle. Were they to be safe during flight they might be so safe that the remaining velocity would not be sufficient to set them off. All fuzes are designed to arm as we say either during travel through the bore or immediately after.

Methods of Arming.

_Spring method._—Let us suppose that after our projectile has started on its way the sliding block is free to move within a cavity at the forward end of which is the anvil. If the projectile comes to a sudden drop or even sudden reduction of velocity the block if unrestrained will, according to the principle of inertia, keep on going till something stops it. The something in this case is the anvil and the fulminate cap is set off. But it is not so simple. For while the projectile is in flight it is acted upon by the air resistance and slows down but the block in the cavity of the head is not subjected to this resistance. It therefore gains on the projectile or creeps forward in the cavity unless restrained as it is by a spring. Now one more point and this type of fuze is complete. We supposed that our block was free to slide. For safety’s sake it is pinned to the cavity. Again we call upon inertia to bread the pin so as to leave the block free to slide. The strength of the pin is calculated so that the force of inertia of the mass of the block is greater than the resistance of the safety pin and when the projectile starts the pin breaks and the spring forces the block to the rear of the cavity until the sudden stop of the projectile permits the block to slide forward as explained. Such a fuze requires a comparatively high initial velocity and is not adapted to howitzers using low muzzle velocities.

There are three other methods in use to arm the fuze. They are =inertia of a sleeve=; =centrifugal force= and =powder pellet system=, that is, combustion of a grain of powder holding the sliding block from the anvil by means of an arm resting against the unburned powder grain. These are more sensitive than the type described.

=In the first system=, a sleeve fitting around the plunger carrying the cap slides to the rear by inertia when the projectile starts and two clips engage in notches on the plunger body making the sleeve and plunger thereafter move as one body, they are thus held together by a plunger spring which before arming held the plunger away from the anvil. The safety spring held the sleeve and plunger away from the anvil and after arming prevents forward creeping by the plunger and sleeve now locked together. Upon striking, the plunger and sleeve move forward as one body and the cap strikes the anvil.

=In centrifugal systems= the primer plunger is kept safely away from the anvil by a lock which is kept in place by springs. When the rotational velocity reaches a certain point the force of the springs is overcome by the centrifugal force and the locks are thrown aside or opened and the plunger is free to move forward on impact.

=In the powder pellet system= (the one largely used by the Germans) there is a well or channel filled with compressed powder, this is set off by a fulminate cap which is fired by inertia, a small plunger-anvil striking the cap. When the powder is consumed it leaves a channel into which an arm attached to the sliding block carrying the igniting fulminate for the charge may slide, thus permitting the block to slide forward to the anvil fixed in the forward part of the cavity. It is held from creeping forward after the compressed powder is burned by a safety spring, thus insuring sufficiently hard an impact to set off the cap.

Heretofore in our service the fulminating cap has been fixed and the plunger carried the anvil or as we call it the firing pin. Such is now the system in our base detonating fuzes, and in our combination fuze.

The new point detonating fuzes are patterned after the French and are practically French fuzes.

Fuzes Classification.

Fuses are classified as:

(a) Percussion if it acts on impact, producing a low order of explosion.

(b) Time when it acts in the air at a certain point of the trajectory.

(d) Detonating when it contains a fulminate which will bring about detonation upon impact.

The detonator may be separate or incorporated in the fuse. For the 75-mm gun and the 155-mm howitzer it forms a part of the fuze.

Many fuzes are armed on set-back. An exception to this is the long detonating fuse, MK 111, which is armed by the unrolling of a brass spiral holding together two half rings made of steel so fitted as to prevent the anvil and the head of the fuse from getting close together. The spiral unrolls when the rotational velocity of the projectile reaches a certain speed, thus drawing away the two steel rings and arming the fuse.

It is of great importance that the spiral spring be not unrolled during transportation or storage. This is prevented by winding a tape of tarred canvas around the spirals, the head being covered by a thin band of tinfoil. Just before loading the projectile the head and tape are removed by pulling the free end of the tape.

The following precautions concerning fuses must be rigidly observed to prevent grave accidents:

1. All detonators and detonating point fuses must be fitted with a felt washer underneath, thus insuring proper seating in the central tube.

2. Never disassemble a fuse by unscrewing.

3. Any fuse, the parts of which have become accidentally unscrewed, must be destroyed at once. If fired it may cause a premature burst; if handled a grave accident may result.

4. Any fuse or projectile which has been fired is dangerous, because it may then be able to detonate by a very slight shock. It is forbidden to touch it.

5. Never remove the tin hood from the long fuse before having screwed the fuse in the central tube.

6. After having removed the tin hood, be sure that the spiral is in its proper position. Never use a long fuse without the spiral.

7. Be sure the men understand that this spiral must not be removed. It has happened that men have removed this spiral, thinking that it was a device similar to the safety ring in trench mortar fuzes, MK VII E.

8. See that the ring of the long fuze which connects the powder train to the fuze body cannot be unscrewed. If it can be unscrewed the fuze should be sent back to the depot.

9. If it is necessary to remove a shell with a long fuze by means of the rammer, be sure to have a special rammer cup in the shape of a hollow cylinder of wood which will fit between the shell and the rammer.

10. Time and combination fuzes cannot be made absolutely water-tight; the cover must therefore not be removed until the projectile is about to be loaded.

Fuse Tables.

Tables showing American and French fuses to be used by our Field Artillery, with information concerning markings, color, time of delay, size of fuse, etc.

DETONATING FUSES.

Letter “E” after mark VII indicates safety device.

Note:—All American point detonating fuses are stamped on head cap in
letters and figures, .125 in high, with name of use, amount of delay,
initials of loader, lot and number; thus: PDF. MIV, xx Delay, FA,
Lot No. xx.

COMBINATION FUSES.

ACTION OF AMERICAN AND FRENCH DETONATING FUSES.

Notes on Ammunition Marking.

=Marks on H. E. Shell.= These are of two kinds.

(a) Stamped marks made with a steel punch on the body of the projectile just above the rotating band. These refer to the manufacture of the projectile.

(b) Painted marks or bands which are clearly visible. They refer to the loading, to the weight of the projectile and to the special purposes for which the projectile is to be used.

Painted marks referring to loading are found on the ogive.

H. E. shells are usually painted red.

Marks referring to weight are painted in black just above the rotating band, as follows:

L.—very light.
+—light.
++—normal.
+++—heavy.
++++—very heavy.

A white cross above these marks means that a plate has been welded on the base. These marks are also painted on the boxes.

Shells fitted with cartridge cases (fixed ammunition) are not painted below the rotating bands.

Special Shell.

Incendiary shells.—These incendiary shells are filled with some flame-producing liquid, alumino thermic charge or incendiary cylinder composed of slow burning linstock and string strongly impregnated with saltpeter.

Markings.—Green with red ogive.

All shells containing black powder are more or less incendiary. Percussion shrapnel is incendiary.

Star Shells.—For 155 howitzer. Upon bursting, they liberate eight white stars fitted with silken parachutes. The stars are projected backward through the base of the projectile at the point of burst. The parachutes open, the stars descending very slowly, illuminating the surrounding objects for about 45 sec. The best height of burst is about 300 m.; the burst interval should not be over 300. These shells are also incendiary. Markings: a blue star and an “E.”

Gas shells are either toxic or tear-producing.

(a) Toxic shells are numbered either 4 or 5. The liquids 4 and 5 volatize, immediately upon contact with the air. The gases are quickly diffused and easily carried by the wind.

Effect.—Liquid 4 acts immediately and is felt instantly.

Liquid 5, on the contrary, works more slowly and its effects are apparent only after several hours. Markings: Green with white bands, and numbers 4 or 5 on the ogive.

(b) Tear shells.—These shells are numbered 11, 12 and 13. They are filled with two liquids, either mixed or separated, one liquid being tear producing, the other smoke producing. When the shell bursts, a greater part of the liquid is volatilized, the remainder being projected to the ground in small drops which volatize with variable speed. Markings: Green with numbers 11, 12 or 13 on the ogive.

Tracer shell.—This shell is fitted with a time fuse which ignites the inside charge, the flames of which pass through the holes in the ogive thus tracing the trajectory. Tracer shells are used in fire for adjustment on aircraft. They are also incendiary. Markings: White with blue ogive. Letter “T” painted on body.

PRECAUTIONS IN SEPARATE LOADING PROJECTILES.

All projectiles must be seated accurately and carefully in loading, otherwise not only inaccurate fire will result but also premature detonations may occur.

Rotating bands should be smoothed and lightly greased just before loading. In transport and in storage the bands should be protected by rope bands, straw tithes, etc., to prevent deformation.

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Field artillery materielChapter XII: Explosives, Ammunition and Fuses

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