Note: Descriptions are shown in the official language in which they were submitted.
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SAFETY SYSTEM FOR A PROJECnLE FUSE
The present invention relates to a safety system
particularly for a small arms projectile for a small arms
weapon.
In our European Patent EP-B-0363079 there is described
a small arms projectile for a smooth bore weapon preferably
fired from a cartridge with a propellant charge therein,
wherein the projectile comprises a generally cylindrical
casing, a warhead assembly, said warhead being hollow to
accommodate an explosive charge and an initiator therefor, the
casing being formed with a firing pin spring biased to a
safety position and locked in the safety position by at least
one spring biased safety pin, wherein the spring biased safety
pin is adapted to release on exit of the projectile from the
muzzle of the small arm weapon.
EP-B-0363079 thus describes a projectile having a
mechanical safety means for retaining the firing pin in the
safety position. The mechanical safety means comprises at
least one spring biased safety pin extending normal to the
axis of the firing pin and located in a radial bore in the
firing pin to prevent axial movement of the firing pin. The
safety pin is radially retained by the cartridge.
There is a drawback associated with this arrangement.
When the projectile leaves the muzzle of the small arm there
is a severe deceleration as it hits still air and this causes
the projectile casing to decelerate and a deceleration force
to be applied to the firing pin in the direction of the
initiator. The shear force applied to the safety pin by the
deceleration between the casing and the firing pin prevents
ejection of the safety pin until the shear force is overcome
by the spring biassing force acting on the pin. The firing pin
is thus retained in its safety position by the safety pin.
Only when the shear force has reduced will the safety pin
release the firing pin. The effect of this is to delay the
arming of the projectile by at least 0.1 seconds (or about 10
metres), or more reliably 0.2 to 0.3 seconds, which equates
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generally to about 20 or 30 metres down range. This means that
targets at short range cannot be engaged and even targets of
25 to 30 metres cannot always be engaged reliably.
A further drawback with this arrangement is that there
is only one safety means for retaining the firing pin in the
safety position. There is a possibility therefore that the
explosive charge could be initiated accidentally if the safety
pin became dislodged from the firing pin due to the cartridge
being damaged, for example.
In order to address these problems EP-B-0363079 suggests
the use of a chemical safety means in addition to the
mechanical safety means. The chemical safety means includes
a layer of combustible adhesive material interposed between
the firing pin and an adjacent hollow portion of the casing.
The combustible adhesive material is connected to a bore at
the rear of the casing adjacent a propellant charge so that
it is activated by the explosion of the propellant charge when
the projectile is fired.
In this arrangement the combustible adhesive material
retains the f iring pin in its safe position for a pre-=
determined period once the projectile has been fired. This
prevents any shear forces being generated between the firing
pin and the safety pin as the projectile decelerates on
hitting still air. In this way ejection of the safety pin
occurs immediately the projectile leaves the muzzle of the
small arm. The time taken for the combustible adhesive
material to release the firing pin and thus arm the projectile
is determined by the characteristics of the combustible
adhesive material.
A problem with this arrangement is that the combustible
adhesive material may deteriorate and become unstable if
stored for a prolonged period, particularly if the adhesive
is in any way defective. This is a major drawback if a long
shelf life is required as is usual for ammunition.
A further problem associated with this arrangement is
that manufacturing constraints can result in the combustible
adhesive material being insufficiently reliable to ensure that
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any delay in arming equates to about 3 metres from the user
when the projectile is fired.
it is known, e.g. from FR-A-0 424 890, US-A-2 537 855 and
US-A-2 564 797, that wholly mechanical contrivances can be
used to egfect safety latching of firing pins in projectile
fuses, and that a firing pins can be used, whilst so latched,
to hold an initiator in a safe condition, against forces
urging it into an armed condition. None of these prior
specifications, however, envisages the provision of increased
safety in handling and in use, by means of plural,
independently active mechanical safety latches which are
designed and configured to be triggered in response to
different events in the firing process.
An object of the present invention is to provide a small
arms projectile which has a safety means for retaining a
firing pin In a safety position prior to firing and releasing
the firing pin on application of acceleration forces
consequent upon on firing.
Another object of the present invention is to provide a
small arms projectile which has at least two mechanically
independent safety means for retaining a firing pin in a
safety position prior to firing.
Another object of the present invention is to provide a
small arms projectile which has a safety means for retaining
a firing pin in a safety position prior to firing which
operates to delay the arming of the projectile on firing in
a more reliable manner than hitherto known safety means.
AMENDED SHEET
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According to an aspect of the present invention there is
provided a small arms projectile for a small arms weapon; the
projectile comprising:-
a generally tubular casing having an axially movable
firing pin;
a warhead having an explosive charge; and
an initiator having safe and armed conditions and
capable, when in its armed condition and when impinged by said
firing pin, of detonating the explosive charge of said
warhead;
wherein the casing also contains safety release means for
releasably restraining the firing pin, against resilient
force, in a safety position whereby said initiator is held in
its safe condition, against an arming force tending to urge
the initiator towards the armed condition;
characterised by the safety release means comprising
first and second mechanical means;
wherein said first mechanical means includes at least one
component constructed to be frangible in response to the
forces experienced on firing of the projectile; and
wherein said second mechanical means includes at least
one component disposed and configured so as to be ejected from
the casing when the projectile leaves the weapon permitting
said resilient force to move said firing pin away from said
initiator to an extent allowing said initiator to be urged
into its armed condition.
Accordingly, the initiator is movable between an unarmed
position and a biased armed position, but is retained in the
unarmed position by engagement with the firing pin in the
safety position. In this way the initiator can not be armed
until the firing pin is moved from the safety position and
disengaged from the initiator.
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Yt will be understood that the abbreviation "g" used
herein represents the acceleration due to gravity. Typically
a small arm projectile will experience an acceleration of
between 10,000g and 15,000g when firad in the chamber of a
small arms weapon. The safety release means retains the firing
pin in the safety position on application of acceleration
forces less than 500g to prevent accidental arming of the
projectile prior to firing. In this way the releasable safety
means will protect the user if the projectile is accidentally
dropped during handling since the acceleration forces applied
to the projectile will generally be less than 500g.
Moreover the firing pin is caused to be released from
said safety position only when the projectile has been fired
and only when both the first and second mechanical means have
been caused, in a predetermined sequence, to no longer be
effective. In this way if one of the mechanical means fails
the other will prevent movement of the firing pin from the
safety position. Since the safety release means has releasable
means which are mechanical, restraint of the firing pin is
improved and problems associated with chemical degradation are
avoided. Furthermore, this can prevent the firing pin moving
towards the initiator when the projectile has been fired and
is still in the chamber or bore of the small arm.
Preferably, said firing pin includes a separate axially
movable base portion.
Conveniently, said frangible component comprises a shear
pin positioned to support said base portion prior to firing
of the projecti"Le.
Thus, the first mechanical means is released from the
firing pin by initial axial movement of the base portion in
a direction away from the initiator. The acceleration forces
applied to the base portion on firing can therefore be used
to release the firing pin from the first mechanical means.
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Thus, the first mechanical means is released from the
firing pin by initial axial movement of the base portion in
a direction away from the initiator. The acceleration forces
applied to the base portion on firing can therefore be used
to release the firing pin from the first me=chanical means.
Conveniently, the strength of the frangible element is
sufficient to withstand acceleration forces applied to the
base portion of up to 500g. In this way, the frangible element
will readily break when the projectile is fired but its
structure will prevent axial movement of the base portion in
a direction away from the initiator prior to firing.
Accordingly, the frangible element prevents release of
the firing pin from the initiator until significant
acceleration forces are applied to the base portion when the
projectile is fired. The acceleration forces applied to the
firing pin, and the base portion, on firing are considerable
and in this way the frangible element can be made sufficiently
strong to withstand shock loads due to mis-handling prior to
firing.
Moreover, the frangible element can be readily fabricated
and its breaking strength reliably controlled during
xnanufacture.
It is preferred that the initiator is urged to move from
its safe condition to its armed condition by rotating about
an axis perpendicular to the axis of said casing.
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Consequently, the initiator can only rotate to the biased
armed position Once the firing pin has disengaged on firing.
In another embodiment, the resilient force applied to the
firing pin is provided by a compression spring having
sufficient stiffness to prevent the firing pin moving into the
initiator due to-deceleration experienced by the projectile
as it leaves the muzzle of a small arm.
Since the firing pin is biased in an axial direction away
from the initiator, this can prevent movement of the firing
pin towards the initiator immediately the projectile exits the
muzzle of the small arm. In this case, the firing pin strikes
the initiator only when the projectile impacts the target.
Conveniently, said second mechanical means includes at
least one spring biased safety pin.
Thus, the safety pin can be radially restrained in a
cartridge from which the projectile is fired. For example,
the safety pin is radially restrained by fins which are in
turn radially restrained by the internal surface of the bore
of the weapon from which it is fired and is released on exit
from the muzzle. The projectile is thus armed either
immediately on exit or within a short distance after exiting
the muzzle of the shotgun.
In preferred embodiments, two spring biased safety pins
are provided for release in opposite radial directions. This
avoids any imbalance of the projectile once it has been
fired.
Preferably, said casing supports a plurality of
stabilising fins constrained to lie against the casing prior
to firing of the projectile, but capable of deployment when
the projectile leaves the weapon; and wherein at least one of
said fins prevents ejection of the ejectable component of
said second mechanical means until said deployment occurs;
the ejection and the deployment being assisted by motion of
said firing pin under said resilient force.
AMENDED SHEET
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In a particular embodiment, said firing pin is provided
with a stabilising disc having a frusto-conical side portion
disposed in contact with the ejectable component of said
second mechanical means.
Conveniently, said initiator is constructed to generate,
when in its armed condition, an initiating explosive charge
in response to impact thereon of said firing pin and
comprises means for causing said initiating explosive charge
to conform to a predetermined shape about an initiator axis
and wherein said initiator axis is misaligned with the axis
of motion of said firing pin when held in its safe conditi.on.
In a particular case, when the axis of said initiator is
misaligned with the axis of motion of said firing pin,
shielding means is interposed between the initiating charge
and that of said warhead.
In a particular embodiment, said initiating explosive
charge is contained in a cup-like structure and said shield
comprises a portion of said structure.
The invention will now be described, by way of
illustration only, with reference to the accompanying
drawings in which:-
AMENDED SHEET
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Figure 1 is a vertical cross-section view of a
projectile of one arrangement removed from a 3" (7.56 cm) 12
gauge cartridge;
Figure 2 is a cross-section view similar to Figure 1 and
shows a projectile of another arrangement;
Figure 3 is a cross-section view similar to Figure 1 and
shows a projectile of a further arrangement;
Figure 4 is a cross-section view similar to Figure 1 and
shows a projectile according to a first embodiment of the
present invention;
Figures 5(a) and 5(b) are partial cross-section views
showing an alternative relationship between initiator and
warhead components to that shown in the figure 4 in safe (but
accidentally triggered) and armed conditions respectively;
and
Figure 6 is a cross-section view showing a further
alternative relationship between the initiator and warhead
components to that shown in figure 4.
In all Figures, similar components of the small arm
projectiles bear the same reference numerals.
With reference to Figure 1, the projectile (1) is formed
with a hollow warhead (2) and a hollow casing (3). The
projectile has a generally cylindrical configuration about a
central axis and is formed in this instance of aluminium
castings. The warhead (2) and the casing (3) are separately
formed castings provided with interlocking means -'n the form
of an externally threaded portion (4) on the casing and an
internally threaded portion (5) on the warhead. The warhead
and casing are joined together immediately prior to assembly
with a 12-bore cartridge.
The casing (3) is provided with an axial bore (6) which
accommodates an axially movable cylindrical firing pin (7).
The firing pin (7) is provided at its operative end nearest
the warhead (2) with a conical needle portion (8) for
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contacting an explosive charge initiator (23) which is
located in the warhead. The firing pin (7) also includes a
stabilising disc portion (9) adjacent the needle portion, a
reduced diameter shaft portion (10) adjacent the stabilising
disc and a base portion (11). The stabilising disc (9) and
base portion (11) have an external diameter which is
substantially the same as the internal diameter of the axial
bore (6). The base potion (11) includes an annular recess
(12) on its side adjacent the reduced shaft portion (10).
In the drawing the firing pin (7) is shown in its safety
position. The firing pin (7) is retained in this position by
a safety release means which includes a primary mechanical
releasable restraining means in the form of two diametrically
opposite spring biased safety pins (13), and a secondary
releasable mechanical restraining means in the form of a
hollow frangible disc element (15).
The safety pins (13) are each located in a stepped
throughbore (16) in the casing (3). The throughbores (16)
have an axis which is perpendicular to the axis of the casing
(3). The safety pins (13) include a pin cap portion (17) and
a shaft portion (18) which locates in the reduced diameter
portion of the stepped throughbore (16). The shaft portion
(18) of the safety pin has an external diameter which is
substantially the same as the internal diameter of the
reduced diameter portion of the throughbore. A compression
spring (19) is provided in the larger diameter portion of the
stepped throughbore (16) and bears upon the pin cap portion
(17) to bias the safety pin (13) radially outwards. The
safety pins (13) are held in the throughbore by engagement
with the firing pin (7). At their remote ends the safety
pins each include a reduced diameter portion (20) adjacent
the shaft portion (18) and a outwardly splayed conical
portion (21) which defines a detent. The reduced diameter
portion (20) extends from the stepped throughbore and engages
the forward axial face (22) of the base portion (11) . The
outwardly splayed conical portion (21) is partly located in
the annular recess (12) and prevents axial movement of the
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firing pin (7) in the direction of the initiator (23).
By virtue of the fact that the safety pins (13) are
retained by the firing pin (7) assembly is simplified
considerably since it is no longer necessary to manually
retain the safety pins (13) in their pre-expanded condition
prior to locating the same in a cartridge for use.
The hollow frangible disc element (15) is positioned
between the base portion (11) of the firing pin (7) and an
annular back plate (24) which is attached to the casing (3).
The strength of the frangible element is such that it
prevents axial movement of the firing pin in a direction away
from the initiator prior to firing and is crushed by axial
movement of the firing pin in said axial direction on firing.
In this respect the frangible element can withstand
acceleration forces applied to the firing pin up to 5000g.
A compression spring (25) is disposed around the conical
portion (8) of the firing pin (7). The compression spring is
retained by engagement with the stabilising disc portion (9)
and an annular retairiing plate (26) which is secured to the
interior surface of the casing (3). The annular retaining
plate (26) includes a central aperture (30) for receiving the
conical portion (8). In the safety position shown the
compression spring does not apply a significant load to the
safety pin.
Located at the remote end of the casing (3) and about
the external periphery thereof are four fins (27) which in
use extend radially outwardly from the body of the casing
(3). The fins (27) are of an accurate configuration such
that in their folded-down position within the cartridge or
barrel for example they will lie over the external periphery
of the casing. To this end the fins (27) are hinged at (28),
the axis of the hinge being slightly angled to the
longitudinal axis of the projectile such that air pressure
will cause the fins (27) to open and to spin the projectile
when it has exited from the muzzle of the weapon. The fins
(27) may be formed of a resilient material such as copper, or
may be moulded into their final form of plastics or a
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mouldable metal such as aluminium. Although the present
invention is described with reference to fins it is
appreciated that the invention also refers to projectiles not
including fins.
The warhead assembly (2) is formed of an aluminium
casting of a generally cylindrical configuration and includes
a domed forward end. The domed forward end conjoins the
cylindrical portion which extends downwardly towards the
casing (3). The hollow portion of the warhead (2) is provided
with an explosive (29), for example A5. The block of
explosive (29) is in this particular embodiment provided with
a central bore (31) for the accommodation of an initiator
(23) which in this particular instance defines part of a
shutter mechanism. The initiator (23) is rotatably mounted on
an axis perpendicular to the axis of the warhead (2) for
movement between the angular position shown and a spring
biased position 90 degrees apart. The initiator (23) is
provided with a wedge shape slot (41) which engages the tip
of the conical portion (8) when the firing pin is in the
safety position. In this way the firing pin (7) retains the
initiator (23) in the unarmed angular position shown. Spring
biassing means (not shown) are provided for rotating the
initiator (23) by 90 degrees to an armed position when the
f iring pin is moved relatively rearwardly. The initiator
(23) is further provided with apertures (32) for receiving
the tip of the conical portion (8) when rotated to the armed
position.
Pre-moulded fragmentation portions (not shown) may also
be formed on the internal or external faces of the warhead
(2). In an alternative the warhead (2) may be formed of a
hard epoxy resin into which a plurality of ball bearings have
been exposed. The advantage of this latter construction is
that the weight of the warhead (2) can be carefully adjusted
by means of the utilisation of the correct weight and number
of ball bearings. Further of course the point of balance of
the projectile assembly can be altered by placing the ball
bearings at various positions in varying numbers within the
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body of the material forming the warhead (2).
In use the explosive charge which is moulded to a
predetermined shape is interfitted in the warhead (2) and the
initiator (23) positioned therein. The casing (3) is
assembled by positioning the frangible disc element (15) at
the base of the bore (6) of the casing (3) once the firing
pin (4) is introduced into the bore (6). The safety pins (13)
are then introduced to the bore (6) and pressed home. With
the cap portion (17) of the safety pins (13) retained in its
pressed-in condition the firing pin (7) is then in retained
in its safety position and the casing (3) and the warhead (2)
may be then screwed together. If in this position the
projectile is accidentally dropped even with the cartridge
casing removed the concussion will not release the firing pin
(7) because the safety pins (13) are inter-engaged therewith
and the frangible disc element (15) is sufficiently strong
not to break. Subsequently the fins (27) are positioned in
their radially inward positions and the device is slipped
into a standard 12-bore cartridge so as to fit on top of the
wadding immediately over the propellant charge.
The cartridge may then be positioned in a standard
shotgun with a cylindrical barrel and fired in a normal way.
On firing the projectile (1) leaves the cartridge (not shown)
and travels along the smooth bore barrel. The acceleration
force applied to projectile in the barrel is typically in the
range 10000g to 15000g. The acceleration force of the firing
pin (7) causes the firing pin (7) to crush the frangible disc
element (15). This allows the firing pin to move in an axial
direction away from the initiator (23). The initiator (23) is
thereby released from its unarmed position and rotates about
its axis through 90 degrees to its armed position. As the
firing pin moves rearwards away from the initiator (23) the
safety pins (13) become dis-engaged from the annular recess
(12). On exit from the barrel the restraint from the internal
wall of the bore is removed and the safety pins (13) are
immediately ejected radially outwards.
On exiting the barrel the projectile decelerates since
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the pressure of the propellant gases in the barrel no longer
act upon it. The deceleration of the projectile urges the
firing pin (7) towards the initiator (23). Contact between
the firing pin (7) and the initiator (23) is avoided at this
stage by the forward motion of the firing pin being countered
by the restraining force applied by the compression spring
(25). When the projectile (1) impacts the target, the
deceleration forces upon it are very much greater and the
associated force acting on the firing pin (7) overcomes the
restraining force of the compression spring (25) and the tip
of the firing pin (7) enters the aperture (32) of the
initiator, thereby causing the charge to explode.
With reference now to Figure 2, the projectile (1) is
substantially the same as the projectile of Figure 1. The
projectile of Figure 2 differs from that of Figure 1 in the
sense that the firing pin (7) includes two separate
components. The conical tip portion (8), the stabilising disc
(9) and the reduced diameter shaft portion (10) are formed as
one component, and the base portion (11) is formed as a
separate component. The base portion (11) is provided with a
central blind bore (60) and an annular flange (61) at its
outer radial periphery on its forward axial face (22). The
reduced diameter shaft portion (10) is located in the blind
bore (60) at its end furthest from the tip portion (8). The
reduced diameter portion has an external diameter
substantially the same as the internal diameter of the blind
bore (60) and includes a shoulder (62) positioned part way
along its length which is urged into engagement with a
stepped annular recess (63) at the opening of the blind bore
(61) by the compression spring (25). The safety pins (13)
have a constant diameter shaft portion (18) which includes a
slot (64). The slot (64) provides a detent which engages the
annular flange (61) to prevent axial movement of the firing
pin (7) in the direction of the initiator (23). In this
respect it will be understood that the slot (64) and annular
flange (61) replace the reduced diameter portion (20) and
outwardly splayed conical portion (21) of the safety pins
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(13) and the annular recess (12) of the projectile of Figure
1.
The projectile of Figure 2 is fired in an identical
manner to the projectile of Figure 1. On firing the
acceleration force applied to the base portion (11) causes
the base portion (11) to crush the frangible disc element
(15). This allows the base portion (11) to move in the axial
direction away from the initiator (23) relative to the shaft
portion (10). As the base portion (11) moves rearwards away
from the initiator (23) the safety pins (13) become dis-
engaged from the annular flange (61). Axial movement of the
shaft portion (10) in the direction away from the initiator
is prevented by engagement of the safety pins (13) with the
disc portion (9). The initiator (23) is thereby held in its
unarmed position by engagement of the tip portion (8) and the
V-groove (41). On exit from the barrel the safety pins eject
radially outwards and the biassing force of the compression
spring (25) urges the shaft portion (10) towards the base
portion (11) in the axial direction away from the initiator
(23). This causes the initiator (23) to be released from its
unarmed position. The initiator (23) then rotates through 90
degrees to its armed position to arm the projectile.
With reference now to Figure 3, the projectile (1) is
substantially the same as the projectile of Figure 1. The
projectile of Figure 3 is different from that of Figure 1 in
the sense that the safety pins (13) have a constant diameter
shaft portion (42) which extends from the cap portion (17).
In Figure 3 the safety pins (13) are radially restrained in
the throughbores (16) by the interfitting cartridge. In the
safety position shown, the safety pins (13) can engage the
forward facing axial side (22) of the of the base portion
(11) to prevent axial movement of the firing pin (7) in the
direction of the initiator (23), and can also engage the
opposing axial side of the stabilising disc (9) to prevent
axial movement of the firing pin (7) in the direction away
from the initiator.
The secondary mechanical releasable restraining means is
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provided by a plurality of circumferentially spaced radially
movable elements (43). The elements (43) have a generally L-
shaped cross-section and are interfitted in an annular groove
(44) formed in a reduced diameter portion (45) of the firing
pin (7) adjacent the base portion (11). The elements (43) are
biased radially inwards into the annular groove (44) by
spring biassing means (46) between the elements (43) and the
casing (3). The elements (43) are accommodated in an annular
recess (47) formed in the bore (6) at the end of the casing
remote from the warhead (2). The annular recess (47) defines
a stepped axial surface (49) in the bore (6). The radial
dimension of the elements (43) is such that in the biased
position shown the elements (43) extend radially outwards of
the annular recess (44) and part way along the axial surface
(48) into the annular recess (47). In this position the
elements (43) define a radial gap (50) between the casing and
their radially outer ends. Also in this position the elements
(43) prevent axial movement of the firing pin (7) in the
direction towards the initiator (23) by engagement with the
stepped axial surface (49). The ?=adial dimension of the gap
(50) is marginally greater than that of the annular recess
(45). The firing pin (7) is axially aligned in the bore (6)
by location of its end furthest from the conical portion (8)
in an aperture (51) provided in the end plate (24).
The initiator (23) is non-movably retained in the
explosive (29) by the annular plate (26).
On firing the projectile (1) leaves the cartridge (not
shown) and travels along the smooth bore barrel. On exit from
the barrel the restraint of the internal walls of the bore is
removed and the safety pins (13) are immediately ejected.
Movement of the firing pin (7) towards the initiator (23) is
then prevented by engagement of the elements (43) and the
axial surface (49) only. As the projectile exits from the
barrel the fins (27) deploy and cause the projectile to
rotate about its axis. At a predetermined point the rotation
of the projectile generates sufficient centrifugal force on
the elements (43) to force them radially outwards against the
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biassing force of the spring biassing means (46). When the
elements (43) engage the annular recess (47) they disengage
from the annular recess (45) and thereby release the firing
pin(7). This will generally occur 0.3 seconds after exiting
the barrel resulting in a delay arming of the projectile
equating to about 30 yards down range which is just far
enough to ensure the safety for the user. Once the projectile
is armed the tip of the firing pin (7) can enter the
initiator on impact with the target being engaged.
The projectile of Figure 3 therefore provides a
projectile for a smooth bore weapon with a novel delay arming
device, and a novel arming device per se.
With reference to Figure 4, in another embodiment the
projectile (1) is formed in a similar way to the embodiments
of Figures 1 to 3 with a hollow warhead (2) and a hollow
casing (3). In the drawing of Figure 4 the detail of the
warhead (2) has been omitted for clarity. The warhead (2) and
casing (3) are separately formed castings with interlocking
means in the form of an externally threaded portion (70) on
the warhead (2) and an internally threaded portion (71) on
the casing (3).
The projectile of Figure 4 is provided with a two piece
firing pin (7). The firing pin (7) of the projectile of
Figure 4 is similar to the firing pin (7) of the projectile
of Figure 2 in the sense that the conical tip portion (8),
the stabilising disc (9) and the shaft (10) are formed as one
component, and the base portion (11) as a separate component.
The shaft portion (10) is located in a central throughbore
(72) in the base portion (11). In the embodiment of Figure 4
the stabilising disc comprises a flat base (73) and a frusto
conical side potion (74) which together provide a recess (75)
on the initiator side of the stabilising disc. A cylindrical
sleeve (76) is located in the bore (6) of the casing (3)
adjacent the firing pin (7). An annular shoulder (77) is
provided at the end of the sleeve (76) nearest the firing pin
tip (8) to receive one end of a compression spring (25). The
other end of the compression spring is located in the recess
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(75) to urge the flat base (73) of the stabilising disc into
engagement with the base (11).
In the embodiment of Figure 4, the firing pin (7) is
retained in the safety position shown by a primary mechanical
releasable restraining means comprising at least one spring
biased safety pin (78), and secondary releasable mechanical
restraining means in the form of a frangible disc element
(79). In this embodiment the safety release means
additionally comprises a tertiary mechanical releasable
restraining means in the form of at least one shear pin (80)
disposed in a recess (83) in the base (11).
The safety pin (78) is located in an inclined
throughbore (81) in the side of the casing (3). At one end
the safety pin (78) engages the frusto-conical side portion
(74) of the stabilising disc (9). The safety pin (78) is
spring loaded in a radially outwards direction by the
compression spring (25) acting on the disc (9) and are
restrained within its throughbore (91) by a fin (27) when in
its folded-down condition as shown.
The shear pin (80) is located in a throughbore (82) in
the side of the casing (3) and extends within a recess (83)
provided in the base (11). The shear pin (80) is provided
with a reduced diameter frangible portion (84) which is
positioned to correspond to the position between the recess
(83) and the throughbore (82).
In the embodiment of Figure 4 the spring biased
initiator (23) is located within the bore (6) of the casing.
In this embodiment the initiator (23) is provided with a
stepped outer surface (85) which is engaged by the tip of the
conical portion (8) when the firing pin is in the safety
position. The initiator (23) is spring loaded to its armed
position which corresponds to the aperture (32) being
aligned with the axis of the firing pin.
The projectile of Figure 4 is fired in an identical
manner to the projectiles of Figure 1 to 3. On firing, the
acceleration force applied to the base portion (11) causes
the base portion (11) to crush the frangible disc element
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(79) and the shear pin (80) to shear. This allows the base
portion (11) to move in the axial direction away from the
initiator (23) relative to the shaft portion (10). Axial
movement of the shaft portion (10) in the direction away from
the initiator is prevented by engagement of the safety pin
(78) with the frusto-conical portion (74). The initiator (23)
is thereby held in its unarmed position by engagement of the
tip portion (8) with the stepped outer surface (85) when in
the barrel of the smooth bore weapon. On exit from the barrel
the fins (27) deploy and the safety pin (78) eject radially
outwards and the biassing force of the compression spring
(25) urges the shaft portion (10) towards the base portion
(11) in the axial direction away from the initiator (23).
This causes the initiator (23) to be released from its
unarmed position. The initiator (23) then rotates through
approximately 30 degrees to its armed position to arm the
projectile.
The embodiment of Figure 4 has been described as
comprising a single safety piri (78) and a single shear pin
(80). In another embodiment these are supplemented by a
second safety pin (78) and shear pin (80) positioned
diametrically opposite each other respectively.
The embodiment of Figure 4 provides a further and highly
significant improvement in the safety of projectiles of this
kind, based upon the important fact that, until the initiator
(23) is permitted to move into its armed position, there is
neither a direct line of impingement of the firing pin (7)
into the initiator nor a direct line of communication between
the initiator and the explosive (29). This is used to
further advantage in the embodiments of the invention
illustrated in part in Figures 5(a), 5(b) and 6.
Referring now to Figure 5(a) , it can be seen that the
initiator (23) is contained within a cup-like construction
(90), made of aluminium, and preferably surrounded with
titanium foil (91), or otherwise coated with or bearing a
layer of titanium, of thickness in the order of 0.001 inch.
The warhead's explosive charge (29) is contained behind a
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shield (92) which adopts a top-hat like shape towards the
initiator (23) with a thinned central portion (93). The cup-
like structure (90, 91) is formed with a lid part (94), which
faces towards the shield (92) so that, in general, when the
projectile is safe, the lid part (94) lies in front of and
parallel to the thinned portion (93) of the shield (92) when
the initiator (23) is not in line with the main charge. By
this means, there is provided a shaping of the initiator's
charge and a shielding of the main charge (29) whereby, in
the event of an accidental triggering of the initiating
charge by some external agency, as indicated by the fracture
of the lid part (94), the energy of the charge does not
directly impact the main charge (29), as it is skewed away
from the direct "line of sight" thereto, and moreover the lid
part (94) of the cup-like structure (90,91) tends to be
opened out, as shown at 94a, and thus provides a strengthened
shield between the initiating charge and the main explosive
charge (29) of the projectile.
Figure 5(b) is identical to Figure 5(a), except that it
shows the armed condition, wherein the cup-like structure
(90, 91) has been allowed to rotate so as to align the charge
(23) with the thinned region (93) of the shield (92). In
this condition, when the initiator charge is fired, as shown,
the opened-out portions of the lid part (94) no longer
overlie the thinned region (93) of the shield (92) and indeed
assist in concentrating the initiator's charge into the main
explosive charge (29) of the warhead; i.e. they provide a
"fire channel" directing the initator's energy to the main
charge.
In the arrangement of Figure 6, the principal difference
from that of Figure 5 is that there is provided a shielding
shutter (95) that is integral with, and thus rotates with,
the initiator (23), thereby obviating the need for the lid
part (94) to the cup-like structure (90, 91) which is
otherwise as described in relation to Figure 5. The shutter
(95) is shaped, dimensioned and crafted of suitable material
to resist or at least lessen the impact on the main explosive
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charge (29) of an accidental discharge of the initiator
charge. In this respect, it can be made relatively bulky
since, of course, it is automatically moved out of the line
of action between the initiator (23) and the main explosive
charge (29) of the projectile when the initiator rotates to
its armed position.
The combination, as shown in Figures 5 and 6, of
shaping, at least to an extent, the initiator's charge,
skewing the shaped charge, with respect to the direct path to
the main explosive charge, in an "unarmed" condition, and
providing additional shielding along the direct path in the
"unarmed" condition, provides a significant degree of
additional safety against unwanted detonation of the main
charge whilst not compromising the sensitivity of the warhead
to detonation in the "armed" condition, when the initiator
charge is rotated to align with the direct path to the main
explosive charge.
It will be understood that the illustrated embodiments
described herein show an application of the invention in one
form only for the purposes of illustration. In practice the
invention may be applied to many different configurations the
detailed embodiments being straightforward to those skilled
in the art to implement.
