Projectile arrangement

A projectile arrangement including a subcaliber projectile body and a segmented, discardable propelling cage sabot provided with a common form locking zone for the transmission of the acceleration forces. To reduce the notch effect on the projectile body, and thus the danger of breakage, due to the conventional thread grooves in the form locking zone, particularly in long, slender penetrators made of a breakage susceptible tungsten heavy metal, a novel form locking connection for the inner form locking region between the propelling cage and the projectile body is provided. This novel form locking connection is characterized in that in the region of the form locking zone beneath the exterior gas pressure receiving surface of the sabot, only the exterior surface of the projectile body is provided with preferably annular microgrooves and the surrounding inner surface of the sabot is smooth. The microgrooves are produced preferably by non-cutting shaping such as, for example, rolling or pressing in, and are configured as arcuate recesses having a relatively flat groove bottom and pointed lands between adjacent recesses. When the projectile arrangement is fired, the microgrooves of the relatively hard projectile body press themselves into the previously smooth interior surface of the relatively soft sabot, and thus produce a corresponding form locking connection only at the moment of firing.

BACKGROUND OF THE INVENTION 
The present invention relates to a projectile arrangement including a 
subcaliber projectile body and a segmented discardable propelling cage 
sabot. More particularly, the present invention relates to a projectile 
arrangement including a subcaliber projectile body, a segmented, 
discardable propelling cage sabot which at least partially surrounds the 
projectile body and a common form locking zone formed in this enclosed 
region for transmitting acceleration forces from the propelling cage sabot 
to the projectile body with the form locking zone being composed, at least 
in part, of corresponding thread grooves or annular grooves structurally 
worked into the exterior surface of the projectile body and into the 
interior surface of the propelling cage sabot or the propelling cage sabot 
segments. 
A projectile arrangement of the above type is disclosed, for example, in 
German Patent No. 2,234,219 corresponding to U.S. Pat. No. 4,671,181. The 
armor piercing projectile disclosed there has a breakage susceptible core 
of tungsten carbide which is encased by a ductile steel jacket. The 
conventional threaded grooves for a form locking connection with the sabot 
are here cut into the outer surface of the steel jacket or casing of the 
projectile body so as to reduce the susceptibility to breakage of the 
brittle heavy metal core and prevent breaking of the core during 
penetration of armored targets, particularly those composed of multiple 
armor plates. Particularly in such armors composed of several substances, 
the different characteristics of the material of the individual armor 
layers, e.g. alternating layers of armor steel, plastic and ceramic 
material, generate strong transverse forces on the slender penetrator rod 
leading to premature breakage and failure of the penetrator. 
This prior art projectile, due to its breakage susceptibility reducing 
steel casing configuration, is excellently suited for use against armored 
targets, but its drawback is the reduction of kinetic energy due to a 
reduction in the average density of the projectile body as a result of the 
"lightweight" contribution of the steel casing. Moreover, the manufacture 
of this prior art projectile body is rather complicated and expensive. 
Customarily, form locking zones are composed of thread grooves and not of 
individual annular grooves. The reason for this is that it is much easier 
from a manufacturing point of view to use available tools (thread cutters) 
for cutting a thread into the central inner bore of the propelling cage, 
which, for example, has a diameter of only 42 mm (equal to the diameter of 
the projectile body) than to cut equidistant annular grooves into the 
inner bore with a rotary cutter that has to be newly placed for each 
annular groove. 
A subcaliber penetrator made of a tungsten alloy and equipped with a 
segmented propelling cage is shown, for example, at page 474 of the 
periodical "Internationale Wehrrevue" (International Weapons Review) Vol. 
5/1988. This penetrator has a form locking zone which is composed of 
cut-in thread grooves and extends over almost the entire length of the 
projectile. If the projectile is employed against multi-armor plate 
targets, the generated transverse forces may lead to premature breakage 
and loss of performance of the penetrator, with the sharp notches in the 
bottom of the thread acting, so to speak, as predetermined break 
locations. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a projectile 
arrangement of the above type which, with guaranteed firing resistance, 
permits economical manufacture and simultaneously reduces the breakage 
susceptibility of the penetrator in connection with transverse stresses 
while increasing its penetrating power in the target. 
The above object is achieved according to the present invention by an 
improved projectile arrangement of the type including a subcaliber 
projectile body, a segmented, discardable propelling cage sabot having at 
least one radially extending flange and a gas pressure receiving surface 
extending rearwardly from the flange, with the sabot at least partially 
surrounding a portion of the length of an outer cylindrical surface of the 
projectile body to provide a common form locking zone extending along the 
surrounded portion, and means within the form locking zone for 
transmitting the acceleration forces from the sabot to the projectile 
body, with this means for transmitting being composed, at least in part, 
of corresponding thread grooves or annular grooves structurally worked 
into the outer surface of the projectile body and into the interior 
surface of the propelling cage sabot. The common form locking zone is 
divided into at least first and second locking zone regions extending over 
its length, with the first form locking zone region being disposed in 
front of the second form locking zone region, extending rearwardly beyond 
the radially extending flange to a length adjacent the outer gas pressure 
receiving surface. The portions of the interior surface of the sabot and 
of the outer surface of the projectile body within the first form locking 
zone region are provided with the above mentioned corresponding grooves, 
the portion of the outer surface of the projectile body within the second 
form locking zone region, and beneath the exterior gas pressure receiving 
surface of the sabot, is provided only with circumferentially extending 
microgrooves, and, the portion of the interior surface of the sabot within 
the second form locking zone region is smooth. 
More generally, the common form locking zone between the projectile body 
and the propelling cage is here divided into at least two form locking 
zone regions (I and II), with the forward form locking zone region (I) 
being provided, over a shortened longitudinal extent, with the 
conventional common and corresponding thread or annular grooves in the 
interior surface of the propelling cage sabot and on the exterior surface 
of the projectile body, while in the rear form locking zone region (II), 
beneath the exterior gas pressure receiving surface of the sabot, flat 
shallow microgrooves are provided only on the exterior surface of the 
projectile body, and the interior surface of the propelling cage sabot or 
propelling cage sabot segments in this rear region is smooth. For 
manufacturing technology reasons and in order to provide for uniform 
release of the propelling cage segments, the microgrooves are preferably 
configured as annular grooves. With this arrangement according to the 
invention, the application of an additional steel casing may therefore be 
omitted. 
In comparison to the conventional tungsten heavy metal penetrators whose 
thread grooves for forming a lock with the propelling cage sabot are cut 
directly into the surface of the brittle tungsten heavy metal, the 
breakage susceptibility of an extremely slender projectile body according 
to the present invention is considerably reduced during the penetration of 
modern layered armors or structured targets involving great transverse 
stresses. This results in an improvement of the final ballistic 
performance. The reduction of breakage susceptibility of the tungsten 
heavy metal penetrators according to the present invention is evident in 
their stress concentration factor for tensile and bending stresses which, 
due to the measures according to the invention, is reduced by about 40% to 
55%. 
Another advantage of the present invention is that with the inventive 
configuration of the form locking zone it is now also possible to employ 
propelling cages which have the required firing resistance and which are 
provided in a basic material, e.g. light metal, plastic, with tensile 
strength increasing longitudinal fibers, e.g., carbon fibers, glass 
fibers, etc. In the past, such propelling cage materials could not be 
employed because cutting in of the form locking zone or, more precisely, 
the thread grooves, by means of a thread cutter caused the supporting 
fibers in the interior surface of the propelling cage to be cut. As a 
result, the tensile increasing effect of these fibers was destroyed again, 
so that only the basic material, e.g. plastic (which by itself did not 
have the necessary strength to transfer the developing push/pull 
stresses), was able to transfer the firing stresses, causing these 
propelling cages to fail. 
Thus, in a propelling cage according to the invention, only a very short 
front form locking region (I) with the conventional thread grooves needs 
to be provided to ensure transport and mutual axial fixing between the 
sabot and the projectile, while this manufacturing work is completely 
unnecessary to form the rear locking region (II) of the propelling cage. 
This noticeably reduces manufacturing costs. 
The inventive microgrooves on the projectile body can advantageously be 
employed equally well for projectile arrangements involving the 
conventional dual-flange propelling cages (push/pull sabot) and 
single-flange propelling cages (pull sabot). 
As one feature of the invention, it is provided that the preferably annular 
microgrooves in the exterior surface of the projectile body are produced 
by non-cutting shaping, for example, by rolling in or pressing in. Due to 
the fact that no material is cut out of the surface of the projectile body 
and a relatively flat or wide groove bottom exists ("soft notch"), the 
breakage susceptibility of the projectile body in the target is reduced 
considerably. Additionally, this measure constitutes an economical and 
waste-free manufacturing method for the form locking zone. 
According to further embodiments of the invention, the form locking zone 
may be provided with a further region which, depending on the type of 
sabot, i.e., pull or push/pull, is disposed either between the above 
described front (first) form locking zone region and the rear (second) 
form locking zone region, or in front of the front (first) form locking 
zone region. This further form locking zone region is provided likewise 
with corresponding thread or annular grooves on both the interior surface 
of the sabot and the outer or exterior surface of the projectile body but 
with these grooves being approximately one half of the height and/or the 
width of conventional grooves provided in the first region. 
The invention will be explained and described below in greater detail with 
reference to embodiments thereof that are illustrated in the drawing 
figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, the reference numeral 10 identifies a projectile arrangement 
which includes a subcaliber projectile body or penetrator 14 made of a 
breakage susceptible tungsten heavy metal (THM), and a segmented, 
discardable sabot 12 which partially surrounds the projectile 14 along a 
portion of the length of its cylindrical outer surface. In order to 
transmit the acceleration forces from propelling cage sabot 12 to the 
projectile body 14 when the projectile arrangement 10 is fired, the 
projectile body 14 and the propelling cage sabot 12 have a common form 
locking zone 16. This form locking zone 16 is generally composed of 
corresponding conventional thread grooves which are cut into the exterior 
or outer surface of projectile body 14 and into the interior surface of 
the propelling cage sabot 12 or, more precisely, the propelling cage sabot 
segments, e.g., three, forming the sabot. 
In the illustrated embodiment, propelling cage sabot 12 is configured as a 
pull sabot having only a single frontal radially extending pressure flange 
18. The three propelling cage segments are held together in the 
circumferential region of the pressure flange 18 by a circumferential 
guide and holding band 22 which simultaneously seals the inner gun barrel 
against the gas pressure of the propelling charge. At its front, pull 
sabot 12 is provided with an air pocket 20 and at its rear with an 
elongate conical portion having an external gas pressure receiving surface 
24 which extends rearwardly from the rear end of the flange 18. In the gas 
pressure receiving surface 24, the dividing grooves between the individual 
propelling cage segments are sealed in the conventional manner against the 
gas pressure by means of a vulcanized-on sealing cuff, for example, of 
rubber, or by means of attached sealing beads. In order to center and 
support projectile arrangement 10 in the gun barrel, the rearward end 
region of propelling cage sabot 12 may be provided with three additional 
radially extending supporting webs 26. To stabilize the projectile in 
flight, the slender projectile body 14 is provided with a fin guide 
mechanism 28 at its tail and possibly with a tracer set 30. 
According to this embodiment of the present invention, the common form 
locking zone 16 is subdivided into two form locking zone regions I and II, 
with only the forward form locking zone region I being provided, over a 
shortened longitudinal extent, with the conventional common, corresponding 
thread grooves in the inner surface of the propelling cage sabot 12 and on 
the exterior surface of the projectile body 14. In the rear form locking 
zone region II, which extends over the major portion of the exterior gas 
pressure receiving surface 24 of propelling cage sabot 12, 
circumferentially extending microgrooves 40 (see FIG. 4a), which are 
preferably annular, are provided only on the exterior surface of the 
projectile body 14, while the interior surface of the propelling cage 
sabot 12, or the propelling cage segments, is smooth. Thus, projectile 
body 14 is provided with the microgrooves 40, which are significant for 
the present invention, only in its rear form locking zone region II which 
extends over approximately two thirds of the total length of the 
propelling cage sabot 12 or more specifically the form locking zone 16. 
FIG. 2 shows, as a further embodiment of the invention, a projectile 
arrangement 10 having a conventional dual-flange propelling cage sabot 38, 
i.e. a push/pull sabot. Propelling cage sabot 38 includes a forward 
radially extending guide flange 32 and a rear radially extending pressure 
flange 34. To provide a gas seal, a circumferential sealing band 36 is 
provided in the circumferential region of pressure flange 34. Starting at 
pressure flange 34, a conical tail section of propelling cage sabot 38 
provided with a conical gas pressure receiving surface 24' extends 
rearwardly. In the manner described above, this gas pressure receiving 
surface 24' is sealed against the existing gas pressure along the dividing 
grooves of the propelling cage segments. 
As a distinction over the embodiment of a pull sabot shown in FIG. 1, the 
forward form locking zone region I provided with the conventional thread 
grooves of the push/pull sabot 38 of FIG. 2 extends over about the front 
two thirds of the length of the propelling cage sabot 38, (i.e., the 
length of the zone 16) while the rear form locking zone region II provided 
with the microgrooves according to the invention, i.e. only on projectile 
body 14, extends over only about one third of the length. 
FIG. 3 is a sectional view of the conventional form locking zone region I 
which has thread grooves 42 cut into the exterior surface of projectile 
body 14 and into the inner surface of propelling cage sabot 12 or 38. Due 
to the chip creating manner of cutting the threads, the lattice structures 
of the propelling cage and projectile body materials are disadvantageously 
weakened in this form locking zone region. The thread notches 42 in the 
exterior surface of projectile body 14 act, so to speak, as inadvertent 
"desired" break locations and constitute a considerable weakening of the 
material. In the form locking zone region I, the conventional thread teeth 
48, 50 have a defined height 46 which approximately corresponds to the 
base width 54 of the respective thread teeth. 
In the case of the region II containing microgrooves 40 in the exterior 
surface of projectile body 14 as shown in FIG. 4a, the situation is quite 
different. The interior surface of the propelling cage sabot 12 or 38 in 
is here smooth. The annular microgrooves 40 in the exterior surface of the 
projectile body 14 are preferably produced by non-cutting shaping such as, 
for example, by rolling or pressing the microgrooves in by means of 
appropriate tools. In this way, the microgrooves 40 are formed as arcuate 
rolled-in portions on a circle having a large radius so as to form a 
flattened groove bottom 62 with pointed lands 56 between adjacent 
microgrooves 40 in the exterior surface of the projectile body 14. With 
this special configuration of the microgrooves 40, the notch and breakage 
susceptibility of the THM penetrator 14 is further reduced. 
The height 44 of the microgrooves 40 here lies approximately between 20% 
and 5%, preferably at about 10%, of the height 46 of the conventional 
thread grooves 42, and the width 52 of the microgrooves 40 is between 30% 
and 10%, preferably about 25%, of the width 54 of the conventional thread 
grooves 42. As a numerical example, a conventional thread as shown in FIG. 
3, for example, has a thread tooth height 46 of about 1.3 mm and a thread 
base width 54 of about 1.85 mm. In contrast thereto, the height 44 of a 
microgroove 40 is about 0.1 mm and its width 52 is about 0.5 mm. 
When compared to otherwise identical parameters, with the microgrooves 40 
according to the invention, the stress concentration factor .alpha..sub.KZ 
under tensile stresses is reduced from 4.7 to 2.1 compared to a 
conventional thread groove (FIG. 3) and the stress concentration factor 
.alpha..sub.KB under bending stress is reduced from 4.0 to 2.3. This 
constitutes a reduction in stress concentration factors of 55% and 42%, 
respectively. 
FIG. 4b shows the conditions during acceleration of the projectile 
arrangement according to the invention in the gun barrel. Upon application 
of the gas pressure to the gas pressure receiving surface 24 or 24', the 
previously smooth interior surface of the relatively "soft" propelling 
cage sabot 12 or 38 (composed, for example, of an aluminum alloy) is 
pressed into the microgrooves 40 on the exterior surface of the relatively 
"hard" projectile body 14 (composed, for example, of THM). This results in 
"impressed" microgrooves or microthreads having a pointed microgroove 
depth 58 and a round microgroove rise 60 in the interior surface of the 
propelling cage sabot 12 or 38. On the basis of this manner of 
functioning, fiber reinforced propelling cage materials can also be 
employed without any problems. 
The form locking zone configuration with microgrooves according to the 
invention is intended primarily for large-caliber ammunition of, for 
example, a caliber of 120 mm employing subcaliber kinetic energy 
projectiles. However, successful firing has also been accomplished in the 
"small" caliber range of 45 mm. 
In the further embodiment of a projectile arrangement 10 including a 
single-flange propelling cage sabot 12 and a projectile body 14 shown in 
FIG. 5, at least one further form locking zone region III is provided 
between the forward form locking zone region I provided with the 
conventional annular or thread grooves 42 (FIG. 3) and the rear form 
locking zone region II provided with microgrooves 40 (FIG. 4a). The 
annular or thread grooves of this further form locking zone region III 
have a height and width of about half the height and width of the 
conventional annular or thread grooves 42 in the forward, first form 
locking zone region I. Moreover, preferably, twice as many thread grooves 
per unit length are provided in the region III then in the region I. In 
this embodiment, the regions I and III each extend over approximately one 
quarter of the total length of the propelling cage sabot 12, i.e., the 
form locking zone 16. However, as shown, the region II extends over 
slightly more than one half of the total length, and the region III is 
slightly longer than region I. 
A corresponding configuration of form locking zone 16 for a dual-flange 
propelling cage sabot 38 is shown in FIG. 6. In this propelling cage sabot 
38, at least one further form locking zone region IV is provided in front 
of a slightly shortened (compared to FIG. 2) form locking zone region II 
provided with the microgrooves 40 according to the invention and even 
ahead of a further shortened (as compared to FIG. 2) form locking zone 
region I provided with the conventional annular or thread grooves 42. This 
form locking zone region IV has annular or thread grooves of a height 
and/or width of about half the height and width of the conventional thread 
grooves 42 in the middle form locking zone region I, and likewise is 
preferably provided with twice as many grooves per unit length. In the 
illustrated embodiment, the regions II and IV each extend over slightly 
less than about thirty percent of the total length of the zone 16. 
FIG. 7 shows a sectional view of the conventional form locking zone region 
I adjacent to one further form locking zone region III according to FIG. 
5, or to the further form locking zone region IV shown in FIG. 6. The 
region I is provided, as shown in FIG. 3, with thread grooves 42 cut into 
the exterior surface of the projectile body 14 and into the inner surface 
of propelling cage sabot 12 or 39. In the form locking zone region I, the 
conventional thread teeth 48, 50 have a defined height 46 which 
approximately corresponds to the base width 54 of the respective thread 
teeth. 
In the form locking zone region III or IV, the annular or thread grooves 
42' have a height 46' and width 54' of about half the height 46 and width 
54 of the thread grooves 42 in the adjacent form locking zone region I. 
The further form locking zone region III or IV is preferably provided with 
twice as many grooves 42' per unit length in comparison to those grooves 
42 in the form locking region I. 
Thus, even though they are reduced in height 46' and width 54', these 
annular or thread grooves 42' are sufficient for transmitting acceleration 
forces from the propelling cage sabot 12 or 38 to the projectile body 14 
in the regions III and IV. At the same time, the grooves 42' are suitable 
to reduce the breakage susceptibility of the projectile body 14, because 
the length of the form locking zone region I of the embodiments according 
to FIGS. 5 and 6 is shortened in comparison with the length of the form 
locking zone regions I shown in the embodiments according to FIGS. 1 and 
2. 
The invention now being fully described, it will be apparent to one of 
ordinary skill in the art that any changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.