Tubes & primers for ammunition

In most breech loading guns it is essential to stop the erosion of the
metal of the vent by preventing the escape of gas through it
when the gun is fired. For this purpose the charges in such
guns are ignited by "vent-sealing tubes." For M.L. guns and
small breech loading guns radially vented, especially those using black powder, the amount of erosion in the vent is not so serious.
The charge is fired by ordinary friction tubes, which are blown
away by the escape of gas through the vent. In all guns axially
vented, vent-sealing tubes, which are not blown out, must be
employed so that the men serving the gun may not be injured.

The common friction tube is a copper tube, driven with powder,
having at the upper end a short branch (called a nib piece) at
right angles. This branch is filled with friction composition
in which a friction bar is embedded. On the friction bar being
sharply pulled out, by means of a lanyard, the composition is
ignited and sets fire to the powder in the long tube; the flash
is conveyed through the vent and ignites the gun charge. For
naval purposes, in order that the sailors should not be cut
about the face or hurt their feet, tubes of quill instead
of copper were used. If friction tubes are employed when
cordite or other smokeless powder charges are used, the
erosion of the vent is very rapid unless the escape of the
gas is prevented; in this case T-headed tubes are
used. They are similar in action to the ordinary type,
but are fixed to the vent by the head fitting a bayonet
joint formed with the vent. The explosion blows a small
ball upwards and blocks the coned hole at the
top of the tube and so prevents any rush of gas.

The vent-sealing tube accurately fits into a chamber formed
at the end of the vent, and is held in place by the gun
lock or some similar means. The force of the explosion
expands the tube against the walls of its chamber, while
the internal structure of the tube renders it gas-tight,
any escape of gas through the vent being thus prevented.

In the English service electric tubes (in the United States
called "primers") are mostly used, but percussion or
friction tubes are in most favour on the continent, and
electric tubes are seldom or never used. There are two types
of electric tube, one with long wires for joining
up with the electric circuit and the other without external
wires. The first type has two insulated wires led into the
interior and attached to two insulated brass cones which are
connected by a wire "bridge" of platinum silver. This bridge
is surrounded by a priming composition of guncotton dust and
mealed powder and the remainder of the tube is filled with
powder. On an electric current passing, the bridge is
heated to incandescence and ignites the priming composition.

In the wireless tube the lock of the gun makes the
electric contact with an insulated disc in the head of the
tube. This disc is connected by an insulated wire to a brass
cone, also insulated, the bridge being formed from an edge of
the cone to a brass wire which is soldered to the mouth of the
tube. Priming composition surrounds the bridge and the tube
is filled with powder. The electric circuit passes from the
gun lock to the disc, thence through the bridge to the body of
the tube, returning through the metal of the gun and mounting.

The percussion tube has a similarly shaped body to the
wireless electric tube, but the internal construction differs;
it is fitted with a striker, below which is a percussion cap
on a hollow brass anvil, and the tube is filled with powder.

With quick firing. guns (that is, strictly, those using metallic cartridge
cases) the case itself is fitted with the igniting medium;
in England these are called primers. For small guns the case
contains a percussion primer, usually a copper cap filled with
a chlorate mixture and resting against an anvil. The striker of
the gun strikes the cap and fires the mixture. For larger guns an
electric primer is used, the internal construction and
action of which are precisely similar to the wireless tube already
described; the exterior is screwed for the case. For percussion
firing an ordinary percussion tube is placed in an
adapter screwed into the case. In some foreign services
a combined electric and percussion primer is used;
the action of this will be understood from fig. 20.

The first cartridges for cannon were made up of gunpowder
packed in a paper bag or case. For many years after the
introduction of cannon the powder was introduced into the bore
by means of a scoop-shaped ladle fixed to the end of a long
stave. The ladle was made of the same diameter as the shot,
and it had a definite length so that it was filled once for
the charging of small guns but for larger guns the ladle
had to be filled twice or even thrice. The rule was to
make the powder charge the same weight as that of the shot.

Cartridges made up in paper or canvas bags were afterwards
used in forts at night-time or on board ship, so that
the guns could be more rapidly loaded and with less risk
than by using a ladle. Before loading, a piece of the
paper or canvas covering had to be cut open immediately
under the vent; after the shot had been rammed home
the vent was filled with powder from a priming horn, and the gun
was then fired by means of a hot iron, quick match or port-fire.

The ancient breech-loading guns were not so difficult to
load, as the powder chamber of the gun was removable
and was charged by simply filling it up with powder and
ramming a wad on top to prevent the escape of the powder.

Paper, canvas and similar materials are particularly
liable to smoulder after the gun has been fired, hence
the necessity of well sponging the piece. Even with this
precaution accidents often occurred owing to a cartridge
being ignited by the still glowing debris of the previous
round. In order to prevent this, bags of non-smouldering
material, such as flannel, serge or silk cloth are used;
combustible material such as woven gun-cotton cloth has also
been tried, but there are certain disadvantages attending this.

All smokeless powders are somewhat difficult to ignite in a
gun, so that in order to prevent hang-fires every cartridge
has a primer or igniter, of ordinary fine grain gunpowder,
placed so as to intercept the flash from the tube; the outside
of the bag containing this igniter is made of shalloon,
to allow the flash to penetrate with ease. The charge for
heavy guns i.e. above 6 inches (150 mm), is made up in separate cartridges
containing half and quarter charges, both for convenience
of handling, and to allow of a reduced charge being used.

The cartridges are made of a bundle of cordite,or other smokeless
powder, tightly tied with silk, placed in a silk cloth bag with
the primer or igniter stitched on the unclosed end; the exterior
is taped with silk cloth tape so as to form a stiff cartridge. For
some of the longer guns, the exterior of the cartridre
is conveniently made of a coned shape, the coned form
being produced by building up layers outside a cylindrical
core. In these large cartridges a silk cord becket runs up
the centre with a loop at the top for handling.

For howitzers, variable charges are used, and are made up so
that the weight can be readily altered. The following typical
instance will serve to show the general method of making
such charges, whether for B.L. or Q.F. howitzers. Small
size cordite is used, and the charge is formed of a
mushroom-shaped core, made up in a shalloon bag; on the
stalk, so as to be easily removed, three rings of cordite are
placed. The bottom of the core contains the primer, and
the rings can be attached to the core by two silk braids.
The weight of the rings is graduated so that by detaching
one or more the varying charges required can be obtained.

For quick-firing guns the charge is contained in a brass
case to which is fitted a primer for igniting the charge.
This case is inserted into the gun, and when fired slightly
expands and tightly fits the chamber of the gun, thus acting
as an obturator and preventing any escape of gas from the
breech. This class of ammunition is especially useful
for the smaller calibres of guns, such as 3-pounder (1.4 kg), 6-pounder (2.7 kg) and field guns, but Messrs Krupp also employ metallic cartridge
cases for the largest type of gun, probably on account of
the known difficulty of ensuring trustworthy obturation
by any other means practicable with sliding wedge guns.

The charges for these cases are made up in a very similar manner to
those already described for B.L. guns. Where necessary, distance
pieces formed of papier-mache tubes and felt wads are used to
fill up the space in the case and so prevent any movement of the
charge. The mouth of the case is closed either by the base
end of the projectile, in which case it is called
"fixed ammunition" or "simultaneous loading ammunition."
or by a metallic cap, when it is called "separate
loading ammunition," projectile and charge being
thus loaded by separate operations.

References