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.CHAPTER
V.
PROJECTILES.
THE projectiles first used in artillery were irregular in
form, and consequently very inaccurate in their fire; and it was night long
before the advantages of the spherical form were demonstrated.
The Sphere presents the minimum surface for a given volume; and the wind,
which causes so much inaccuracy in elongated projectiles, has comparatively but
little effect on the round one, which, having its centres of gravity and figure
more nearly coincident than any other, presents, when it rotates, an equal
surface always to the action of the air. If it strikes any object in its flight,
it is less deflected from its course than one of any other form; -- an important
fact, since ricochet firing is of great importance in war, it being sometimes
the only means of reaching an enemy behind obstacles.
Oblong.-- When the design is to strike an object direct, however, the
sphere is no longer the most advantageous form. For, by making the projectile
elongated and pointed, the resistance of the air is very much diminished; and
additional weight can be added without increasing the cross-section of the
projectile; thus increasing its power of overcoming the resistance, and the
penetration of the projectile when it strikes.
Taking the most approved form for elongated projectiles, the
resistance to it is found to be about 1/3 of that offered to a spherical ball of
the same diameter. The resistance to the spherical ball is ½ of what one of its
great circles would experience. So that the resistance to a projectile moving
point first is just 1/6 of what it would be were it moving with the base to the
front. The resistance increases as the surface against which it acts becomes
more nearly perpendicular to. the direction of this resistance. Hence, if the
projectile becomes flattened by the rammer in loading, the resistance is very
much increased.
Stone balls were first used, but were found too brittle to resist the
force of powder, and not sufficiently dense to produce the proper effect when
striking.
Leaden balls, although snore dense and less brittle than stone, cannot be
used in large guns on account of the softness of the metal, and the ease with
which their form is changed when striking against objects offering even but
slight resistance. Consequently, lead can be used advantageously only in small
-arms, and against animated beings.
Iron.-- The use of iron in the manufacture of balls, dates from the
XIV. century. The density and resistance of this metal allow the use of large
charges. Consequently the effect of the ball is much greater, and it has an
effect on stone walls vastly superior to stone balls.
Shells.-- Soon after the adoption of iron balls, attempts were made to
throw explosive globes, designed to act against an enemy behind his works. The
first mention made of hemis at the
siege of St. Boniface, Corsica, in 1421. They were formed of two hollow
hemispheres of stone, or bronze, joined by means of a hinge, a circle of iron,
and keys. The fuze to this rude shell consisted of a sheet -iron tube,
inclosing the priming, and riveted to one of the hemispheres. These were
succeeded by shells cast in a single piece, either of bell-metal or iron,
possessing much more solidity than the others, which often burst before leaving
the piece.
Canister .-- In firing against masses of troops at short distances, the
advantages of a divided projectile, such as to strike a number of points at the
same time, was early seen. The first used consisted of a box filled with old
scrap -iron, which soon gave place to small iron balls, which of course carried
further, and had many other advantages. Gibbon mentions the use of such
canisters at the defense of Constantinople in 1453; and the grapeshot, canister,
and spherical case or shrapnell, of the present day. are all modifications of
them.
Projectiles are divided into two general classes, viz.,
solid shot and hollow shot or shells.
Solid Shot are divided into balls, or those used in heavy guns, and bullets,
which are used with small ones. Solid shot being more dense than shells, are
much more accurate in their fire, especially at great distances. They have
greater power of overcoming the resistance of the air, and consequently greater
velocity and penetration when they strike. They are made of cast iron, and used
principally in guns. Their fire increases in accuracy and range as the
size or calibre increases.
The resistance of the air is the principal cause of
the decreased velocity and accuracy of balls. This resistance is proportional to
the surface. a ball twice the size of another, meets with much greater
resistance; but its weight is 8 times as great, which enables it to overcome
that resistance with greater ease.
Two projectiles moving with the same velocity, the retarding
force will be proportional to their surfaces, or to the squares of their
diameters. But the velocity which will produce this retarding force is equal to
the force divided by the mass of the projectile ( V= F/M, since F = MV), which
is itself proportional to the cube of the diameter into the density. Hence the
losses of velocity caused by the resistance of the air in the two projectiles,
are proportional to the squares of the diameters, divided by the cubes of these
diameters into the densities, or inversely proportional to the diameters into
the densities.
With the same density, but different diameters, the loss is
inversely proportional to the diameter; and the largest ball loses the least.
Consequently, for great ranges, large balls must be used.
With the same diameter, but different densities, the most
dense loses the least, so that dense projectiles have the greatest range.
And finally, in order that two balls, moving with the same
velocity, shall be equally retarded, the respective products of their diameters
by their densities, must be equal to each other. Thus, in order that a cast
-iron ball shall be retarded the same as an ordinary musket-bullet of 0.65 inch
in diameter, .both having the same velocity, we must have the following
relation:
x x 7.207 =0.65 x 11.352,
in which, a is the diameter of the iron ball; 7.207 is the
density of iron, and 11.352 is the density of lead. Deducing the value of x, we
have x=.65 x 11.352/7.207 = 1.02 or a little over one inch. The weight of such a
ball would be=pi/6 (1.02)³ .2607 =.145 lb. or some - thing over two ounces,
instead of about one ounce, which is the weight of the musket -bullet. Hence,
cast-iron bullets for muskets would be inferior to leaden ones, as their loss of
velocity is greater and the deviations more considerable; wherever, therefore,
balls are used approaching the size of the musket -bullet, lead is the best
material.
Spherical projectiles, to be serviceable, should offer
sufficient resistance to the action of the powder, in order that the initial
velocity to be given them, may be great enough to produce the necessary results,
such as penetration, &c. They should be as near spherical as possible;
homogeneous in their structure; have their centers of gravity and figure as near
together as possible; be as dense as possible, present no roughness on the
surface, which would be liable to injure the piece; and if hollow, should have
capacity to hold sufficient powder to fulfill the object for which they are
fired.
The resistance offered by the air to shells, decreases as
the interior is decreased or the thickness of metal increased. If we wish to
find the diameter of a solid shot corresponding to a shell of a given density, the density of the shell being
2/3, that of the shot, we will have, calling x the diameter of the shot, and D
that of the shell, x= 2/3 D.
To find what should be the density of a 12 -pound shell, in
order that it experience the same resistance from the air as a 6 -pound shot, we
will obtain, by calling d the required density, 4.52d =3.58 x 7.207, and
consequently, d =5.7, that is, the density of the shell should be the 5.7 /
7.207 = 0.79 part Of that Of the corresponding shot, and as that weighs 12.3
lbs., the weight for the shell will be 12.3 x 0.79 = 8.5 lbs.
From what precedes it will be seen that lead, if hard
enough, would be the best metal to use in projectiles, forged iron the next, and
then cast iron, which is much cheaper than forged.
As early as the time of Louis XIV., hollow elongated projectiles
were made use of, and must have been in great favor, since they appear to have
been made of all sizes. The pointed form was found to aid the projectile passing
through the air. The interior was divided into two compartments, the front one
filled with powder and balls, the rear one with powder only, thus throwing the
center of gravity well forward. Had these shells been provided with grooves on
the rear part, they would have fulfilled all the conditions laid down on page
116, and have probably given better results.
As the length of the ball increases, its mass and weight
increase, whilst the resistance remains the same. Doubling the weight of the
ball thus renders the resistance of the air relatively one-half less. If, for
example, the oblong bullet weighs 730 grains, and the spherical one of the same
calibre, 412 grains, the resistance to the first will be only the 412/730, part
of what would be offered to an oblong one of the same weight as the spherical
ball. But this last experiences a resistance three times that of the elongated
one of the same weight, so that the oblong bullet of 730 grains experiences 1/3
x 412/730 of the resistance (or about one fifth) offered to the spherical bullet
of the same calibre (old).
The resistance is, however, still very great to pointed
projectiles, it being estimated that it reduced the range of one experimented on
in France, to one -half of what it would be in vacuo.
In projectiles which are designed to act against animated
beings, the diameter may be decreased considerably, and the length increased
without impairing their efficiency. But for those which are to act against
fortifications, masses of earth, &c., a certain calibre is necessary. Were
the projectile of too small a diameter, and pointed in form, it would go through
the obstacle without breaking or splintering it much, whilst spherical
projectiles crush and break; into pieces the objects struck, and they also have
the advantage of deviating less from ricochets, which are very important in war,
either as marking the point of fall, and allowing a rectification of the aim, or
as a means of reaching an enemy behind his works.
Calibre.- The calibre of balls is expressed by the round number of
pounds contained in them. Those used in our service are the following. They are
made of cast iron.
128, 68, 42, 32, 24, 18, 12, and 6.
Shot to be used at sea, and on the seacoast, should be
somewhat smaller than those for service inland, on account of their liability to
oxidize from the dampness of the atmosphere. (For dimensions, see Appendix, page
442.)
Bar or chain shot consists of two hemispheres or balls connected
by a bar of iron or chain. They take a rotary motion when fired, and are used
with great effect against the masts and rigging of vessels, but are very
inaccurate in their fire.
A stand of grape consists of nine shot of a
size appropriate to the calibre used, which are held together by two rings, and
a plate at each end of the stand connected by a rod or bolt. (For dimensions,
see Appendix, page 443.)
Quilted grape consists of an iron plate and an upright spindle around
which balls are placed and held in their positions by a canvas bag which is tied
to the plate and then quilted. on to the balls by means of strong twine, which
is finally tied around the mouth of the bag. This kind is no longer used in our
service.
Canister Shot is a tin cylinder with iron heads, filled with balls packed
in with saw -dust. The heads are movable, and the edges of the tin are turned
down over them to hold them in their places. The balls are made of such a size
that seven of them can lie in a bed, one in the middle, and six around, making
the diameter of the balls about one -third that of the bore. These balls are all
made of c«t iron, except for the mountain howitzer, the canisters for which are
filled with musket -bullets, which, as has been shown, meet with less resistance
from the air, and retain their velocity longer than cast-iron balls
of a much larger size. It would be better to make them of wrought iron
for field-guns, as is done in France; as, besides being more dense, they would
be less likely to break and injure the bore of the gun than cast-iron ones. For
dimensions, see Appendix, p. 444.)
It has been shown (p. 140) that a cast -iron ball 1.02 inch
diameter loses as much velocity from the resistance of the air as the ordinary
musket -bullet, therefore where balls smaller than this are required, the musket
-bullet should be used.
Bullets are divided into spherical and elongated. They are made of lead,
and used in small-arms. The calibre of spherical bullets is determined by the
number which a pound of lead will make. Thus, our common musket is said to carry
seventeen to the pound. But this is almost entirely superseded in use by the
elongated bullet, the calibre of which is determined by its diameter or its
weight in grains, usually by the former. There are but two sizes now in use in
our service (see pp. 119 - 120); and in time it is the intention to reduce these
to one, which may be used for either rifle, rifle -musket, or pistol. But the
bullets, although precisely the same on the exterior, differ in the size of the
conical opening, and in weight, the lightest being fifty grains less than the
other, the weight of which is five hundred grains. (Figs. 75 and 77, page 120.)
This difference was found necessary in order that the small charge of the pistol
should have force sufficient to press out the sides of the bullet and rifle it
properly, which it was found sometimes not to do with the thicker one. The
longer these bullets are made the less is the loss of velocity - from the
resistance of the air, from the greater power of the bullet to overcome this
resistance; and were it not for the want of consistency and the softness of the
lead, this lengthening would be theoretically unlimited. But they soon become
inconveniently long, and liable to be injured in shape, and it is found that,
beyond a certain length and a certain number (three) of grooves, the bullet does
not carry well. The length of those in our service has been fixed by experiment
at 1.1 inch for the large, and 1.05 inch for the small size.
Rifles and Artillery .-- Since the recent improvements in projectiles and long
-range rifles, it has been customary to underrate the importance of the
artillery arm on a field of battle, and the assertion is frequently heard, that
the use of the rifle will supersede entirely the use of field-pieces in war,
since it has a greater range and more accuracy than the field -pieces now in
use. This, I am convinced, is a mistaken view. It is true that long -range
rifles are destined, in the hands of skilful marksmen, to play a very important
part in battle, by picking off the cannoneers of the artillery from points
beyond the range of this last, provided they can once get their sights
properly arranged for that distance; but they have first to get their range. To
do this, as very few men are at all accurate in estimating distances, trials
have to be made; and the bullet makes so little dust in striking, and what it
does make is scarcely visible at 1,000 yards, that it affords the marksman but
little opportunity to correct his aim. In the mean time the gunner is getting
his range, which he is enabled to correct from the striking of the ball, which
can be seen as far as it goes, and when he once gets it, and that not accurately
and precisely, as the rifleman must, but approximately, he is enabled to let
loose among his opponents a charge of from thirty to eighty musket -bullets at a
time, or send a solid shot through
them with sufficient force to disable, perhaps kill, half a dozen, and
disorganize as many more by its moral effect.
When the rifleman gets his sight adjusted to the proper
range, it is an easy matter for the artilleryman to increase or decrease his
distance, rendering new adjustments of the sight necessary, and all this in the
heat and confusion of a combat.
These facts, to say nothing of the great physical, as well
as moral effect of a rapid and well-directed fire of half a dozen guns upon a
body of infantry, seem to demonstrate that the importance of artillery upon the
field of battle is increased rather than diminished, and should urge to
improvement in its range and efficiency rather than to its abandonment
nd underrating.
The uncertainty of properly adjusting the sight of a rifle
in the heat of battle, must be evident to every one; and it is stated that the
present emperor of France, fully alive to the fact, has discarded the back
elevating sights altogether on his rifles, or very much reduced their
graduation, preferring to leave the aiming to the judgment of the men rather
than possibly lead them into error by the presence of the sight. Napoleon's
recent address to his troops, in Italy, warning them that long -range rifles are
formidable only at a distance, and that great dependence must still be placed
upon the skilful use of the bayonet, is a hint which they seem to have
followed.
It has been stated that the fire of hollow shot increases in
accuracy as it becomes heavier, or the interior space decreases. This also
increases the penetration. On the other hand, the interior space should be large
enough to contain sufficient powder or incendiary composition to produce a
proper effect; whether this be to produce a great number of splinters with a
certain velocity, to destroy by the explosions field -works, or to set fire to
shelters occupied by the enemy. The last objects will be attained best by shells
having a large interior space. Experiment shows that hollow projectiles fulfil
the necessary conditions best when their mean density, or real weight, is equal
to 2/3; that of the solid shot of the same diameter.
Divided.-- Hollow shot are divided into shells, spherical case or
schrapnell, carcases, and grenades; all of which are made
of cast iron. Their calibre is determined either by the number of pounds
contained in a solid shot of the same size, or by the number of inches in the
diameter of the shell itself.
Shells are hollow shot, the interior space being formed of a sphere
concentric with the outer surface, thus making the sides of equal thickness. In
mortar shells the thickness is uniform throughout, but other shells are
reinforced at the eye, to give a greater bearing surface to the fuze and
prevent its being blown in by the force of the heavy charges used in guns and
howitzers. They have a conical opening or eye, used to load the shell,
and in which is inserted the fuze
to communicate fire to the charge. Its axis is always coincident with a, radius
of the sphere.
The eye should decrease in size with trio interior
space. Too large an opening might allow the escape of the gas without bursting
the shell. It should not be too small, as this would prevent the use of a proper
thickness in the fuze.
Shells have sometimes been reinforced with a culot,
or increased thickness of metal opposite the fuze hole, for the purpose of
strengthening that part most exposed to the shock of the powder, especially in
pieces with long, narrow chambers, which were formerly employed, and with an
idea that it would cause the shell to fall with the fuze up, and prevent the
failing of the fuze, from becoming stopped up with dirt when it fell.
The objections to the use of the culot are: that it
separates the centre of figure from that of gravity, thus diminishing the
accuracy of fire and the velocity, by the increased resistance
of the air, due to the irregular movement of the eccentric projectile;
that the culot being thicker, presents more resistance to the powder than the
other portions of the shell, and consequently a less number of pieces are
formed. Experiments go to show that an exploding shell cracks generally through
the fuze hole. The culot is not used at all in our service.
The resistance offered by a shell to the force of the powder
increases with the thickness of its sides. The number of pieces produced when it
explodes is the greater, all else being equal, as the metal is more brittle, and
the eccentricity of the shell is less.
The French sometimes make their shells for sea-coast service
with an additional eye, at an angle of 45º with the other, called a charging
hole, the object being to have the fuze already fitted. in, ready for use,
and allow the charge to be poured in just before the shell is wanted. It is
found that the powder, when left in the shell for any length of time, rapidly
deteriorates, from the dampness of the sea air. This arrangement, however, has
the disadvantage of requiring the fuzes to be cut beforehand and without knowing
at what distances they are to be used.
The following are the shells used in the United States
service:
For mortars, 13 -in., 10-in., and 8-in., Fig. 95, Pl. 14;
the last used also in the 8 -in. siege howitzer.
“ Columbiads, 10 -in. and 8-in., Fig. 96, Pl. 14.
“ Guns and howitzers, 42, 32, 24, 18, and 12 -pdrs., Fig.
96, Pl. 14.
The sides of mortar shells are thinner than the
corresponding sizes for guns and howitzers,
as larger charges are used with these.
The mortar and columbiad shells are handled by means of two
ears placed one on each side of the eye, which serve for attaching a pair of
shell -hooks. The other shells have no ears, but rope handles are fixed to the
tin straps which fasten them to their sabots. (For dimensions, (see Appendix, p.
443.)
Spherical Case , or Shrapnell shot, as they are called, after the
English general who brought them to perfection, are thinsided shells, in which,
besides the bursting charge, are placed a number of musket-bullets. Their sides
are much thinner than those of the ordinary shell, in order that they may
contain a greater number of bullets; and these acting as a support to the sides
of the shell prevent it from being broken by the force of the discharge. The
weight of the empty case is about ½ that of the solid shot of the same
diameter. (For dimensions, see Appendix, p. 443.)
The calibres in use in our service are:
The 8-in.-- 42, 32, 24, 18, 12, and 6 -pdrs. Fig. 97, Pl.
14.
They are all reinforced at the eye, to give a greater
bearing for the fuze. Lead being much more dense than iron, the schrapnell is,
when loaded, nearly as heavy as the solid shot of the same calibre; but on
account of the less charge which it is necessary to use to prevent rupturing the
case, their fire is neither so accurate nor the range so great as with the solid
shot. But when the shrapnell bursts just in front of an object, the effect is
terrific, being in fact much the same as a discharge of canister from a piece at
short range.
The range and effect are both much increased by the present
method of loading (page 443), which places the powder entirely free from contact
with the bullets, and it is in consequence not liable to be ground up by them
whilst being transported, or when the shot is fired. These advantages are
further increased by the adoption of the admirable Barmann fuze, which can be
screwed into its place beforehand, and gauged on the field, in a moment.
The charge used in these shells is sufficient simply to
rupture the case, and release the bullets at the proper point in front of the
object. Their execution depends, then, upon the velocity which the shell has at
the moment it bursts.
The Barmann fuze being adopted, the reinforce at the eye
becomes useless, and may as well be dispensed with in the large calibres to
allow more room for bullets. This would also make the firing more accurate, as
the shell would be more concentric.
Carcasses Fig. 98, Pl.14, are shells having, besides the usual eye, three
others, which are placed at equal distances apart, and tangent to the great
circle of the shell which is perpendicular to the axis of the first eye. They
are filled with combustible composition, primed at the four holes with quick
-match and mealed powder, and are used to set fire to an enemy's works, the
additional holes being to allow a more rapid escape of the flame.
Grenades , Fig. 99, Pl.14, are of two kinds. The hand-grenade is
a small shell thrown from the hand or in baskets from the stone mortar. Rampart-grenades
are larger, and are used to roll down a breach in its defense, to throw over
the ramparts, &c. Any kind of shell, unfit for firing either from being
defective in form or solidity, may be used for the purpose. 6 -pdr. spherical
case shot may be used as hand -grenades.
War-rockets .-- a. rocket is a projectile which is set in motion
by a power residing within itself. It therefore performs the part both of a
piece and a projectile. The cases for war-rockets are made of sheet -iron and
lined with paper or wood veneer to prevent the composition from touching the
metal and rusting it, which would destroy the missile. They are filled with a
composition of nitre, sulphur, and charcoal, in the same way as described for
signal rockets; but are generally filled solid by means of a ram or press, and
the core then bored out. At the top end either a solid shot or shell is placed,
and riveted to the case, a recess being cut out of the lower part of the
projectile, which is there cylindrical, to fit into the ease. When a shell is
used, it is perforated through the diameter which coincides with the axis of the
ease, and a fuze driven into the opening next to the composition. When the
composition burns out, fire is communicated to the fuze, which, in its turn,
explodes the charge in the shell. The hole at the top of the shell enables the
fuze to be regulated, by boring it out in part or altogether. The top hole is
then closed with a wooden plug or a screw.
The dimensions of rockets are indicated either by the weight
of the projectile or the diameter of the case, in inches.
Two kinds of rockets have been used in this country, the Congreve,
and Hale's.
Congreve's Fig. 100, Pl.14, has, like the ordinary sky -rocket, a directing
-stick, but instead of being tied to the outside of the case, it is inserted in
a socket placed directly in rear of the case, the flame escaping through holes
around this. This modification was
introduced by Sir William Congreve, who was also the first one in modern times
to make use of metal cases; but he is not the inventor of the rocket, which has
been known from time immemorial in China and India, in both of which it had been
used as a war missile.
These rockets have been made of immense size, the largest
weighing as much as three hundred pounds, but have never been adopted to any
very great extent; for, although very formidable and destructive, especially
when used against cavalry, their fire is very inaccurate. The motion of the
rocket is due to the pressure on the case produced by the reaction of the gas
escaping through the vents, and depends upon the mechanical principle of the
equality between action and reaction.
Rockets are fired from troughs or tubes mounted on
adjustable tripods, so that the necessary
angle of elevation can be given to them. They may also be simply laid upon the
ground, having the necessary slope, and fired singly or in volleys. In the
latter case, they are connected by a piece of quick -match communicating with
the priming, by lighting which the rockets go off in rapid succession.
Special troops have, in some of the European powers, been
formed and armed with these projectiles, which are carried in wagons. Each man
carries into action several rockets ready for use, and tied to his saddle. In
this country, however, no such organization has been made; although, rockets
were used to a limited extent in the war with Mexico.
In the Austrian service they appear to have been adopted to
a much greater extent than anywhere else. But they are there made with a shell
very much larger than the diameter of the case, to which it is fastened with tin
-plate straps. They are fired from tubes into which they are placed from the
front, with the shell, which is too largo to enter, projecting from the mouth.
Large angles of elevation are used, and the rocket, after
accomplishing a short range, drops its shell with its fuze (previously
regulated) burning.
Hale's (Fig. 101, Pl.14) differs from any other rocket in
having no guide -stick. Direction is given to the rocket by imparting the rifle
motion to it. This is effected by placing in the rear part a number of holes
oblique to the axis. The gas, escaping through these, acts upon the air and
gives the rotary motion to the case, whilst it is propelled forward by the
action, or rather reaction, of the gas escaping at the main hole at the
extreme end. Within a year past, these oblique holes have been changed from
their position in rear of the rocket, reduced to two in number, opposite the
center of gravity, and fire instead of being communicated at the end is applied
at one of these holes, and rapidly spreads in both directions in the interior.
Hale's rocket, by dispensing with the long and unwieldy guide -stick, is a
great improvement; but it is not the only one which has been made. The great
difficulty in rcket-firing, is to get them to start in the right direction. Long
before it has attained anything like its maximum velocity, it commences to move.
and the moment it loses the support of the tube or through, it begins to fall or
"dip," and before the constantly increasing velocity is great enough
to overcome this disposition, the rocket will probably ricochet; and this,
especially with Hale's, is apt to throw it very much out of its course, and add
to its otherwise inaccurate firing. Mr. Hale has striven to overcome this
difficulty by placing his rocket behind a strong spring, which holds it until it
has acquired force enough both to overcome its inertia and the strength of the
spring, when it is released with a much greater velocity, and but little of its
former disposition to " dip."
A great objection to these rockets made with metal cases, is
that from the expansion and contraction of the metal, cracks and flaws are
formed, after a time, which give passage to the flame, increase very rapidly the
rate of combustion, and sometimes cause the rocket to explode like a charge of
gunpowder. Rockets, when kept any length of time, are particularly liable to
this accident. It is stated that in New Mexico, where the climate is very dry,
the common sky-rocket cannot be kept for any length of time without being
subject to the same defect; and they are sometimes restored to their former
condition by soaking them for a short time in water, and then drying them.
MANUFACTURE
OF PROJECTILES.
In the manufacture of projectiles, iron moulds have
sometimes been used, but are found to make an inferior, brittle article, liable
to be easily broken, principally from the more rapid cooling of the metal. The
moulds are now made of sand, similar to that used in casting guns; though a less
refractory sand is needed, as the mass of metal is less, and possesses,
consequently, a less amount of heat. It is, as before, mixed with clay -water,
to give it form and consistency.
Moulding .-- The model consists of two polished hemispheres of
copper, which, fitted together by means of a groove in one and projecting edge
in the other, form a perfect sphere. One of these hemispheres is placed on a
board or other plane surface. Over this is placed one-half of the flask,
a sheet-iron box in two parts (Fig, 102, Pl. 14) made to fit each other, for the
purpose of containing the mould. Each half has a movable bottom, taken off when
the sand is placed in. Each one of the copper hemispheres has in the bottom a
hole and thread of a screw, c, into which a handle can be placed to lift the
model out of the mould, and on the outside at d, a corresponding hole and thread
into which the handle b is now screwed. A round stick, a, is held in a suitable
position against the board on which the flask; rests, and the moulding is driven
compactly in until the flask is full to the line e f, when it is accurately
levelled off; the handle b unscrewed,.and with the stick a removed. The bottom
is placed on, secured in its place, and the whole turned over; the board, g h,
taken off and the other half -model and flask adjusted on top of the first ones,
dry sand being sprinkled on top of the half -mould formed, to prevent the
other from sticking to it. Fig. 103, Pl. 14. After screwing the handle of the
other half -model in its place, this flask is filled, the handle removed, and
bottom put on in the same way as at first.
The top half is then taken off and turned over, and both
half models are taken out by screwing in the handle at a, and lifting them up
carefully so as not to break the mould; a passage is cut at c, across from the
channel b, and if casting solid shot, the hole left by the handle at d is closed
with sand. Any parts which have been broken away are now repaired by hand, and
the whole interior is covered with coke -wash; the mould is placed in an oven to
be thoroughly dried,* after which the two parts are fastened together, with the
two apertures b and e uppermost.
* Until recently, the moulds were not dried before casting, but casting after the mould is dried is found to produce a much smoother, better alloy than when cast wet or "green".
Casting.-- The metal, in a proper state of fluidity, is brought from the
furnace in a bucket or ladle, formed as shown in Fig. 104, Pl. 14, of iron,
coated with clay, having wrought -iron or wooden handles, and poured into the
mould at f, entering at the side to prevent injury to the form. As it rises, the
air escapes at e, which also serves as a dead -head to collect the scoria, if
any enters, and furnishes metals to supply the shrinkage caused by cooling.
Core.-- In casting shells, the mould is made in the same way, but a core
is needed in addition. This is a sphere of the proper size, made by
compressing the moulding composition on a stem b, Fig. 106, Pl. 15, by
means of two cups, Fig. 105, Pl. 14, the requisite compression being given by
screws placed at a, b, and c. This core is, by means of a gauge, placed exactly
in the centre of the mould, and supported in that position by the stem placed in
the hole, which, in casting solid shot was closed. The core being subjected to
greater heat than the other portion of the mould, should be made of a more
refractory sand. The stem, besides supporting the core, forms the fuze -hole for
the shell. It is formed of a thick wire covered with the moulding composition.*
After the casting has become cool, the core is broken up and removed; and the
projecting portions at the gate, c, Fig. 103, Pl.14.and around the base where
the two halves join, are taken off with a chisel.
* The stem is sometimes made hollow, as at a, a, a, Fig. 106, Pl. 6, to allow the escape of any gases which may form from the effect of the heated metal.
Polishing -- A number of the balls are now placed in a large revolving iron
cylinder, which, by friction, polishes and makes the surface more uniform; after
which, and before any lacker or grease is placed on them, they are inspected.
All projectiles for large ordnance are made of, cast -iron,
though other metals have been used, and, until recently, the Mexicans used
copper to a great extent, and, perhaps, still do so.
Materials .-- All projectiles for our service for cannon are manufactured in
private foundries, and inspected by officers of the ordnance, before they are
received into service. After which they are covered with a coating of lacker,
and placed in piles of different sizes until they are wanted.
The iron used in the manufacture of projectiles should be
what is commonly termed grey or mottled, and should be of good
quality, especially for spherical case -shot, which requires more care on
account of the thinness of the sides.
Inspecting .-- The manner of inspecting shot and shell, and the instruments
used, will now be described. To ascertain if they are of the proper weight,
several parcels, of from twenty to fifty, are weighed, being taken from the pile
indiscriminately. If any are found smaller than the rest, they are weighed
separately, and rejected if they fall short of the proper weight by a small
fraction, which has been successively reduced as the improvements in the art of
casting enabled a higher standard to be reached. They generally exceed the
required weight.
To find the weight of a cast -iron shot of any diameter,
multiply the cube of its diameter in inches by 0.134. The result will be the
weight in pounds. If the weight of a shell is required, use in this rule the
difference between the exterior and interior diameters in place of the diameter.
1/6 pi D³ being the solid contents of any sphere, and 0.9607 = the weight of a
cubic inch of cast -iron, the weight of a cast -iron sphere will be =1/6 pi D³
x 0.2607 =(3.1416 / 6) X 0.2607D³ = 0.134D³.
The multiple in the case of lead balls is 0.2142.
To find the diameter of a cast -iron shot of a given weight,
reverse the rule: divide the weight by 0.134, and the cube root of the quotient
will be the diameter in inches.
The shot is inspected while perfectly clean, and before
becoming rusty, so that the eye can detect any flaws or imperfections in the
metal. If any attempts have been made to fill these with iron, cement, &c.,
the shot is at once rejected without further examination. Such holes as are
found are probed with a steel punch, or struck with the pointed end of
the inspecting hammer.
This hammer weighs about half a pound, and is flat at one
end for sounding shot and shell, and conical at the other. Cavities over 0.2 in.
deep, cause rejection.
The Ring-gauge Fig. 107, Pl. 15, is a ring of iron with a
wooden handle, used to determine the diameter of the shot. Two sizes are used.
The largest is 0.02 or 0.03 in. greater than the true diameter of the
shot, and the smallest 0.02 or 0.03 less than the true diameter. The shot must
pass in any direction through the large gauge, and not at all
through the small one. (For dimensions see Appendix, p. 444.)
The size of grape and canister shot is determined by using a
large and small gauge attached at the opposite ends of the same handle, Fig.
108, Pl.15. The surface should be smooth and free from seams. The
Cylinder-gauge, Fig. 109, Pl.15, is a cast -iron cylinder with reinforce bands
on the exterior, and an interior diameter equal to the diameter of the large
ring -gauge. This is placed on blocks of wood, with one end about 2 inches
higher than the other, in such a position as to be easily turned so that it will
not be worn in furrows by the shot rolling through it. The shot is then rolled
through. They should pass through without sticking or sliding. In this
last case, it shows that some one diameter is too large. In case they stick,
they are pushed out from the lower end with a rammer. (For dimensions see
Appendix, p. 444.)
The soundness or strength of shot is proved by dropping them
from a height of twenty feet, on an iron block, or rolling them down an inclined
plain of that height against a shot at the bottom.
Shells and hollow shot are inspected in the same way, but
require in addition the following instruments: --
Callipers , Fig. 110, Pl.15, for measuring the thickness of the metal at
the sides, which consist of two bent arms movable on a common pivot, and
showing on a graduated are the thickness of the metal; or, Fig. 111, Pl.16, of
one straight arm which is placed tangent to the outside of the shell, and one
bent, which is inserted in the shell, the thickness being shown on a graduated
limb which joins the two.
Callipers, Fig. 112, for measuring the thickness of the shell at the
bottom, which consist of two straight arms connected by a circular piece.
One of these arms is inserted in the shell, and the other, being movable, shows
on a graduated side the thickness of the metal.
Gauges Fig. 113, for the dimensions of the fuze-hole end thickness of
metal at that point.- These are pieces of plate metal having inclined sides
to fit the fuze -hole, with the proper dimensions marked on them for each
calibre. A pair of hand bellows, and a wooden plug to fit the fuze-hole,
and bored through to receive the nose of the bellows.
The shell is sounded with the hammer, to see if it is free
from cracks. The position and dimensions of the ears are verified; the thickness
of metal is measured at several points on the great circle perpendicular to the
axis of the fuze-hole, at the bottom and at the fuze-hole. The diameter of the
fuze-hole, which should be accurately reamed out, is measured with the gauge;
and the soundness of the metal about the inside of the hole is ascertained by
inserting the finger.
The shell is now placed in a tub with water, deep enough to
cover it nearly to the fuze -hole; the bellows and plug are inserted in the fuze-hole,
and air forced in. If there are any holes in the shell, bubbles of air will rise
through the water. Should there be any cavities in the metal, those portions
will dry more slowly than the others.
Shot and shells rejected in the inspection are marked with a
cold -Chisel with an x – the Shells near the fuze -hole) the shot near the gate,
or point where the metal entered the mould. The shot and shell, as soon as
received, are covered with a coating of lacker, which should be renewed from
time to time as required.
Preservation -- Shot and shell are preserved in piles according to kind
and calibre, under shelter if practicable, where there is a free circulation of
air. The width of the bottom her may be from 12 to 14 - balls, according to the
calibre.
The ground should be prepared by raising it a little above
the surrounding surface to throw off the water, leveling it, ramming it, and
covering it with a layer of clean sand, coal -ashes, or any thing else which
will not promote vegetation. Bury a her of unserviceable balls about 2/3, of
their diameter in the sand. Place the fuze holes of shells down in the
intervals, and not resting on those below. Each pile is marked with the number
of balls it contains. The base may be made of brick, concrete, stone, or with
braces and borders of iron.
Grape and canister shot should be oiled or lackered, put in
piles or in strong boxes, on the ground floor, or in dry cellars, each box
marked with its kind, calibre, and number.
Each pile should contain only one kind and calibre of shot.
There are three kinds of piles used, with oblong, square,
and triangular bases; and it often becomes necessary to calculate rapidly the
number of balls contained in them. To do this, the following formulas are used:-
In an oblong pile which has a rectangular base, let n = the
number of balls in the width of the base. In the triangular end the number of
balls in the different horizontal layers will increase in arithmetical
progression from 1, at the top to n, which is the bottom row. The sum to the nth
term, or the number in the end, will then be = (n(n+1)) / 2 . Representing by m
the number of balls contained in the upper edge of the pile, that in each of the
lower edges parallel to it will be represented by m+ n - 1. Considering the pile
as a triangular prism whose bases are oblique to each other, its contents will
be equal to the number in one of the triangular bases (the end of the pile),
multiplied by the mean of the three parallel edges, representing the altitude of
the prism, -- that is, by (3m +2n -2 ) / 3. Hence, the number of balls is
=(n(n+1)) / 2 ((3m + 2n -2)) / 3 and the rule, -- Multiply the number of balls
in a triangular face by one -third the sum of the three parcel edges.
If the base of the pile is square, m becomes = 1, and the
formula reduces to n (n+1) / 2 (2n+1) / 3 and if it is triangular, m is = 1 as
before, and another of the parallel edges reduces to 1, while the third is = n,
and the formula becomes n (n+1) / 2 (n+2) / 3
If we have given the number of balls to be piled and the
width of an oblong pile, m the length of the top row, and the two sides of the
base can be at once deduced from the formula.
If a pile consists of two piles joined at a right angle, to find the contents of it calculate the number contained in one as a common oblong pile, and the other as a pile of which the three parallel edges are equal.
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