An improved small caliber armor piercing projectile (10) having a fin stabilized sub-caliber high density rod penetrator (11) and an adequately large tracer cavity (23). The tracer cavity does not degrade the armor penetrating capability of the projectile. The rod penetrator core is supported structurally during gun launch by a minimum weight segmented sabot (13) which engages the barrel rifling, followed by a solid plastic obturator (15) which provides an uninterrupted gas seal and holds the segmented sabot components together around the rod penetrator prior to launch. The solid obturator is made from a low ductility homogenous plastic or plastic reinforced composite and is blown apart upon muzzle exit by entrapped propellant gas pressure retained in an internal aft cavity (19). The plastic obturator are located behind the structural sabot so that the propellant gas pressure will maintain the obturator under hydrostatic compression while in the barrel to ensure projectile in-bore stability. Upon muzzle exit, the fractured obturator and segmented sabot components freely discard from the flight projectile without introducing trajectory disturbances.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to discarding sabot projectiles, and more 
specifically to sub-caliber fin-stabilized armor penetrating projectiles, 
which contain therein rod penetrator cores, and an integral tracer of 
suitable pyrotechnic composition. 
2. Description of the Prior Art 
Three types of armor piercing projectiles are currently utilized in small 
caliber gun systems. One of the designs is of a conventional projectile 
shape and is full-bore diameter, consisting of a combination of high 
strength steel or high density material as a penetrator swaged or inserted 
into a suitable jacket or sleeve material. At the projectile base is an 
opening for a tracer cavity of adequate depth and diameter to provide a 
clear visual trace of the entire projectile trajectory. This type of 
full-bore projectile utilizes the high density or high strength penetrator 
and to some extent the jacket or sleeve material and its geometry to 
affect armor penetration. This type of projectile has severely limited 
armor penetration capability at target engagement ranges beyond several 
hundred meters, due to its high drag configuration. 
It has been demonstrated that sub-caliber high density rod type penetrators 
are capable of penetrating significantly more armor than the full-bore 
projectiles at target ranges beyond several hundred meters. This is due to 
the high density rod's more efficient armor penetration geometry and the 
greater mass per cross sectional area of the sub-caliber rod flight 
projectile, which results in it losing less velocity from aerodynamic 
drag. To take advantage of the rod's high ballistic coefficient and to 
provide increased initial launch velocities, sabots were designed to 
encapsulate the rod penetrator during handling, storage, and gun firing, 
and to discard shortly after exiting the muzzle, thus allowing only the 
rod penetrator to continue in flight toward the target. One type of 
discarding sabot projectile has been demonstrated in small caliber guns to 
provide increased armor penetration over full-bore projectiles. This is 
the Armor Piercing Discarding Sabot (APDS) projectile, which utilizes a 
spin stabilized sub-caliber penetrating core as the flight projectile. 
APDS projectiles using high density rod penetrators have been developed 
for guns from caliber 5.56 millimeter through caliber 120 millimeter. 
Given aerodynamic considerations, APDS projectile designs below caliber 25 
millimeter do not allow the inclusion of a tracer cavity without degrading 
penetrator performance. The tracer cavity in these projectiles 
significantly reduces the available high density rod material required for 
armor penetration. 
It has been demonstrated that armor piercing fin stabilized discarding 
sabot (APFSDS) projectiles penetrate more armor at greater ranges than 
spin stabilized APDS projectiles, due to the longer allowable penetrator 
lengths that can be launched and flown to the target with accuracy and 
stability. APFSDS projectiles utilizing high density sub-caliber rod 
penetrators have been developed for both rifled barrel and smooth bore 
guns from caliber 25 millimeter through 140 millimeter, and these designs 
have permitted the incorporation of an adequate tracer cavity in the rear 
of the flight projectile without degradation of the rod's armor 
penetration performance. Flechette type APFSDS projectiles utilizing high 
strength or high density rod penetrators have been developed for small 
caliber 5.56 and 7.62 millimeter rifle systems, but without allowance for 
a tracer cavity in the flight projectile. 
Fin stabilized APFSDS projectile designs incorporating an adequate tracer 
cavity and developed for larger caliber systems do not efficiently scale 
down to small caliber projectiles due to the complexity of their sabot 
geometries which were optimized for the unique parameters of the larger 
caliber systems. Early fin stabilized APFSDS projectile designs for 
smaller caliber 5.56 and 7.62 millimeter guns did not provide for a tracer 
cavity in the rear of the flight projectile. 
A more effective and efficient fin-stabilized, discarding sabot projectile 
incorporating an adequate tracer cavity with a deep armor penetrating 
projectile for small arms applications has been disclosed in U.S. Pat. No. 
5,297,492 (Buc). This design overcomes many of the shortcomings inherent 
in earlier small arms APDS and APFSDS projectiles, such as: faulty 
structural design, poor sabot discard, reduced projectile accuracy at long 
range, low muzzle velocity due to high sabot parasitic weight, and 
inadequate armor penetration. Although a good start in the right direction 
for small caliber APFSDS projectiles, this design requires the use of 
several high precision manufactured obturator components, to ensure 
adequate performance and safety reliability. Reducing the complexity of 
the current state-of-the-art in obturator design will result in greater 
projectile performance, achieved with less expensive components, 
assemblies, and manufacturing processes. 
Accordingly, it is advantageous to provide an armor piercing fin stabilized 
discarding sabot (APFSDS) projectile for small caliber guns which 
minimizes sabot parasitic weight and structural complexity, facilitates 
rapid sabot separation upon muzzle exit without introducing trajectory 
inaccuracies for the rod projectile, maximizes armor penetrator weight and 
length, and provides for an adequate tracer cavity in the rear of the 
flight projectile. 
SUMMARY 
Several objects and advantages of my invention are to provide a small 
caliber Armor Piercing Fin Stabilized Discarding Sabot Tracer (APFSDS-T) 
projectile which overcomes the problems set forth in detail herein above. 
The projectile assembly of this invention is made up of a sub-caliber high 
density rod penetrator of length substantially longer than its external 
diameter, with an internal tracer cavity in the based portion, an external 
threaded or grooved region along the central portion of its long axis, and 
aerodynamic contouring of the forward nose portion; a stabilizing fin 
appendage of substantially full-bore diameter with a through-hole along 
its central axis to provide for continuation of any tracer cavity and for 
affixing to the aft portion of the rod penetrator; a segmented structural 
sabot of low density metallic material with an internal threaded or 
grooved cavity along its symmetric axis for attachment to the rod 
penetrator; the sabot is of length less than or equal to its external 
diameter, with a central bulkhead region of substantially full-bore 
diameter which engraves into the barrel rifling, a tapered concave ramp 
aft of the bulkhead, and a substantially equal length tapered concave ramp 
forward of the bulkhead; behind the sabot is a solid, continuous, 
unsegmented low density plastic obturator of substantially full-bore 
diameter which engraves into the barrel rifling and has a forward tapered 
surface for mating with the tapered aft ramp of the sabot with an 
interference fit, and a through-hole along its central axis with internal 
diameter slightly less than the external diameter of the rod penetrator 
for an interference fit. This solid obturator has an aft opening internal 
cavity for trapping propellant gases during firing. 
In the present series of discarding sabot projectiles for small arms 
applications, to facilitate obturator separation without introducing 
trajectory inaccuracies for the rod projectile, obturator components are 
segmented longitudinally into equal parts, or longitudinally notched at 
uniform intervals to provide fracture points. These early design 
approaches have been used with the understanding that small caliber rifle 
barrels impart insufficient spin and muzzle gas pressure to cause a solid 
mass of obturator material to fracture upon release from the barrel 
confines. For this reason, obturators are segmented, or notched to create 
a lower fracture threshold in previous inventions. 
Notching plastic obturators has been shown to be a serious disadvantage in 
previous discarding sabot designs, resulting in faulty structural 
integrity, poor sabot and obturator discard and poor trajectory accuracy. 
Notched obturators and sabots are typically placed forward of the surface 
upon which the propellant gas pressure acts. In other words, the structure 
is not under hydrostatic pressure. Orthogonal states of stress are not 
equal, and should the material fail, a crack could propagate to 
catastrophic proportions. Notched structural components cannot be placed 
under hydrostatic pressure, since the notch removes some material. Under 
hydrostatic pressure, the material will fail and flow into the notched 
area, resulting in the structure collapsing under the load. 
Segmenting is very different from notching. Segmenting slices the material, 
but does not remove material, as does a notch. A structure may be either 
partially or completely segmented through its section, depending on the 
strength requirements. A segmented structure will not collapse, and a 
crack will not propagate under hydrostatic pressure, since there is no 
where for the material to flow. However, when not subjected to hydrostatic 
pressure, a partially segmented structure may behave similarly to a 
notched structure. 
When a plastic obturator or sabot is notched or partially segmented, the 
structural component is being required to perform contradictory functions. 
Theoretically, the notch or partial segmenting introduces a predetermined 
fracture point, with a fracture strength less than the adjacent material. 
This fracture point, however, must still withstand the rotational forces 
imparted to the structure during down-bore travel. Upon muzzle exit, this 
same structure fractures at the notch or segment due to the same 
rotational forces, once the confines of the barrel are removed. 
Unfortunately, the rotational forces are a maximum at the muzzle, where 
the spin rate is a maximum. And since the structure is supposed to not 
break in the barrel under the same spin rate induced forces that break it 
outside of the barrel, the structural demands placed upon the notch or 
partial segment are mutually exclusive. The structure must either break in 
the barrel, exactly at the muzzle, or not at all. 
If the structure does not break prior to muzzle exit, ram air forces will 
eventually strip if off of the sub-projectile. However, serious trajectory 
disturbances will result. If the structure breaks prior to muzzle exit, 
the sub-projectile may dislodge from the sabot or obturator and damage the 
barrel. At a minimum, in-bore failure will result in poor trajectory 
accuracy. It is a statistical impossibility to design the fracture point 
to fail exactly at the muzzle every time under all conditions of operation 
and material quality variations. Therefore, notching or partially 
segmenting structural components under the notion of easing sabot discard 
is a faulty design practice. 
The effective solutions involve placing a solid un-segmented obturator, or 
a combination of fully segmented and un-segmented obturator components 
behind a segmented structural sabot, where the obturator is subjected to 
hydrostatic pressure so that the material will not flow and fracture, and 
where there is an independent mechanism, trapped propellant gas, to 
fracture a solid obturator component upon muzzle exit. 
Fully segmenting portions of obturator components reduces the sabot and 
obturator discard problems, but introduces design, manufacturing, and 
assembly complexities. In U.S. Pat. No. 5,297,492 (Buc), to retain the 
segmented portions of the sabot and forward components of the obturator 
prior to launch, the aft portion of the obturator is a solid plastic ring 
which mates over the aft portion of the segmented obturator components. 
This obturator ring has an aft cavity which retains propellant gas 
pressure and expands radially to seal against the barrel wall during 
launch. Upon muzzle exit, the entrapped gas pressure is sufficient to 
fracture this solid obturating ring permitting it and the other obturator 
and sabot components to separate freely from the rod projectile. 
This approach of segmenting some of the obturator components, while 
incorporating a solid, unsegmented obturator ring to retain the segmented 
components during launch, has been shown to be functional and effective 
when using a certain class of plastic obturator materials. Homogenous 
plastic materials, such as those known under commercial names as Nylon, 
Delrin, Lexan, Ultem, and others which have a strain elongation to failure 
from twenty-five to seventy-five percent work well in this obturator 
design. One of the most important properties in the proper selection of 
obturator material is that it has an ultimate failure elongation less than 
approximately seventy-five percent. The reason for this is that the solid 
obturator ring must not break too late after muzzle exit. The more ductile 
the material, or the higher its elongation to failure, the more time it 
requires to strain and break due to the entrapped muzzle gas pressure. 
Using these materials, the obturator must be segmented in the forward 
region, since spin rates and entrapped muzzle gas pressure are 
insufficient to overcome the strength and elasticity of these homogeneous 
plastic materials if used unsegmented. However, these materials are 
sufficiently weak so that the small solid plastic obturator will quickly 
fracture due to entrapped propellant gas upon muzzle exit. 
It is not possible, however, to use such ductile plastic materials in an 
obturator design which eliminates the forward segmented components. A 
fully solid, unsegmented plastic obturator, using these ductile materials 
and this previous design, will not fracture upon muzzle exit, when fired 
from a small caliber rifle, resulting in poor projectile accuracy and 
reduced effective range. 
It is advantageous, therefore, to develop an obturator design, for small 
caliber rifle application, which incorporates a much more simplified 
obturator assembly, eliminating segmented obturator components and the 
solid obturator retaining ring, yet results in clean sabot and obturator 
separation and reduced trajectory disturbances to the flight projectile. 
A solid, unsegmented obturator design and material combination has been 
achieved in this invention. Unlike the present series of discarding sabot 
projectiles, this invention places a solid, one piece plastic obturating 
material aft of the structural sabot where it is subjected to the high 
propellant gas pressures during travel down the barrel. In this 
configuration, the plastic material behaves as a fluid would behave under 
hydrostatic pressure. Under hydrostatic pressure, the plastic material can 
fail structurally, but a crack cannot propagate since the three orthogonal 
components of the state of stress are equal and under compression. The 
preferred materials for use in a one piece solid obturator in this design 
are reinforced plastic composites, and very low elongation homogenous 
plastic materials. 
Reinforced plastic composites exhibit ideal mechanical properties for use 
in a one piece, solid obturator. Reinforced composites have high 
compression and tensile strength, yet very low elongation to failure, most 
of them from one to three percent strain. Plastic composite materials 
which function well in this design include those known commercially as 
Linen-Phenolic, Fiber Glass, Glass-Filled Nylon, Glass-Reinforced Nylon, 
Glass-Reinforced Ultem (polyetherimide), Glass-Filled PEEK 
(polyetheretherketone) Resin, Glass-Reinforced Polycarbonate, 
Glass-Reinforced Polyester, Glass-Reinforced Polyethylene, Fiber 
Reinforced Epoxy, Fiber Reinforced Thermoplastic and others with a strain 
to failure of less than twenty-five percent elongation. Homogenous plastic 
materials which have high strength, advantageously low elongation to 
failure, and are suitable for use in this invention, include commercially 
known plastics such as Acrylic, Torlon (polyamide-imide) Epoxy, 
Thermoplastic, and Phenolic, and others with a strain to failure of less 
than twenty-five percent elongation. The use of low elongation to failure 
homogenous plastic and plastic composite materials permit the 
simplification of discarding sabot obturator design and complexity, while 
ensuring in-bore structural integrity and stability, and clean sabot 
separation upon muzzle exit. For these reasons, this invention provides 
unique, unexpected, and useful results applicable to small caliber 
discarding sabot projectile design. 
It is an objective of this invention to provide a subcaliber 
fin-stabilized, armor piercing, discarding sabot projectile which 
incorporates a lightweight one-piece, continuous, solid obturator which 
engages the barrel rifling and is located aft of the structural sabot. 
These and other objects of the invention will be better understood by 
reference to the following detailed descriptions, accompanying drawings, 
and claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a cross-sectional view of my invention, an armor piercing fin 
stabilized discarding sabot tracer (APFSDS-T) projectile 10, providing an 
advantage not heretofore obtained in small caliber gun systems with the 
present series of discarding sabot projectiles. The major components or 
parts of this new projectile include an elongated rod penetrator core 11, 
made of high density material such as tungsten alloy, depleted uranium 
alloy, or hard steel. With respect to travel direction 26, attached to the 
rear portion of the penetrator core with a suitable interference fit is a 
stabilizing fin appendage 25. The interference fit is provided by conical 
boattail section 28 and a lesser diameter cylindrical section 27 at the 
rear of the rod penetrator. The boattail section allows for reduced 
aerodynamic base drag. Sub-caliber flight projectile 22 is the assembly of 
the rod penetrator and the stabilizing fins. The stabilizing fins are made 
of high strength aluminum or steel. In the base portion of the rod 
penetrator is a tracer cavity 23, which is filled with a suitable 
pyrotechnic composition. The fin appendage contains a through-hole 24 for 
continuation of the tracer cavity. Attached to the outside of the 
penetrator core with a threaded or grooved interface 21 is a segmented 
structural sabot 13. The segmented sabot is made from strong, low density 
material such as aluminum or magnesium alloy, and is segmented 
longitudinally into a plurality of equal parts. The segmented sabot has a 
central bulkhead region 16 of diameter sufficient to permit it to engage 
the barrel rifling, flanked by a concave aft sabot ramp 14 and a concave 
front sabot ramp 12. These ramps are concave in form to give the sabot the 
lowest weight and highest strength combination for the launch mass and 
acceleration of the rod penetrator. The concave aft ramp also provides a 
strong interlocking surface with the aft obturator component. The aft 
sabot ramp is of substantially equal length to the front sabot ramp so 
that the total sabot weight is minimized. Located behind the sabot is a 
solid obturator 15. The solid obturator is made from low density material 
such as a reinforced plastic composite or a homogenous plastic material 
with an ultimate failure strain of less than twenty-five percent 
elongation. The external diameter of solid obturator 15 is sufficient to 
permit; it to engage the barrel rifling. The forward convex surface of the 
solid obturator mates with the concave aft sabot ramp. The internal 
cylindrical surface of the solid obturator mates with the external surface 
of the rod penetrator with a tight interference fit, forming a continuous 
gas seal around the projectile base from the bore to the rod penetrator. 
An aft cavity 19 is provided opening to the rear in the solid obturator to 
entrap propellant gas pressure during down-bore travel to seal the barrel 
during launch and to fracture the obturator material when the projectile 
is free of the barrel muzzle. Sufficient in-bore stability for the 
projectile during launch is provided by the combined bore-riding lengths 
of the solid obturator and the segmented sabot. As shown in FIG. 1, the 
obturator 15 has a bore-riding surface having a length greater than its 
bore diameter. The external diameters of the solid obturator and segmented 
sabot are sufficiently full-bore to permit each to engage the barrel 
rifling to provide tight in-bore integrity of the projectile. 
FIG. 2 shows a cross-sectional view of an existing APFSDS-T projectile 30 
which does not provide the advantages heretofore obtained with my 
invention. The projectile in FIG. 2 utilizes a multipiece plastic 
obturator assembly, comprised of forward segmented plastic obturator 18, 
followed by an aft solid obturator ring 17. The use of this multipiece 
obturator assembly is required to ensure in-bore structural integrity of 
the sabot and obturator components and proper obturator and sabot discard 
when using obturator materials with an ultimate strain to failure of 
greater than twenty-five percent elongation. The use of more brittle 
obturator materials, those with less than twenty-five percent elongation 
to failure in the solid obturator ring results in premature obturator 
failure during launch, resulting in the loss of in-bore structural 
integrity, low muzzle velocity, and poor accuracy. The use of too ductile 
an obturator material in this configuration, those materials with greater 
than seventy-five percent elongation to failure, results in the solid 
obturator ring stretching and venting the entrapped propellant gas 
pressure. As the entrapped propellant gas pressure vents, the solid 
obturator ring may not fracture before it can clear the stabilizing fin 
appendage. If the solid obturator ring stretches, but does not fracture, 
and impacts the fins, the projectile trajectory will be disturbed, 
resulting in loss of accuracy. 
Although this prior design can be made to function safely and reliably 
using a precisely defined range of ductile obturator materials, the use of 
this multipiece obturator is more costly in terms of the required 
manufacturing and assembly processes which ensure the necessary high 
quality control. Ensuring that obturator material ductility specifications 
are achieved and maintained within the required range during all phases of 
manufacturing and storage also adds considerable quality control costs. 
My invention, by simplifying the obturator assembly and lowering the 
material ductility requirements to that of a very brittle material, 
contains the necessary design and material improvements to make an 
APFSDS-T projectile fully functional, less expensive to manufacture and 
inspect to high standards of quality control, and a more cost effective 
armor penetrator in small caliber guns. 
Operation of the Invention 
When the invention, projectile 10 as shown in FIG. 1, is fired in a gun, 
the expanding propellant gases exert a positive force on the projectile 
base. The material mass per base area of rod penetrator 11 is greater than 
the combined material mass per area of solid obturator 15 plus segmented 
sabot 13. This mass per area imbalance results in a positive traction 
force in interface 21 between the rod penetrator and the sabot. The 
material strengths and groove form are chosen such that the interface will 
not fail in shear and allow the sabot and penetrator to move relative to 
each other in the longitudinal direction. This results in the sabot and 
the rod penetrator traveling down-bore as an assembled unit. The gun 
barrel prevents the sabot segments from moving radially outward away from 
the rod penetrator during down-bore travel. The gas pressure which forces 
the projectile down-bore forces solid obturator 15 forward against sabot 
13, as all components travel down-bore. As the projectile begins its 
down-bore travel, sabot bulkhead 16 engages the barrel rifling developing 
a radially compressive force keeping it in tight contact with rod 
penetrator 11. Similarly, solid obturator 15 engages the barrel rifling 
developing a radially compressive force keeping it in tight contact with 
the sabot and the rod penetrator. As the obturator is forced forward, 
concave aft sabot ramp 14 forces solid obturator 15 to ride radially 
outward ensuring positive radial pressure against the barrel wall thus 
providing a tight assembly against the sabot and penetrator and a seal 
against the propellant gas pressure. 
When the projectile exits the barrel muzzle, the trapped gas pressure in 
cavity 19 causes solid obturator 15 to fracture radially outward away from 
rod penetrator 11, since the gun barrel is no longer present to restrict 
radial movement. The fracture of the relatively long and thick obturator 
section is achieved due to the very low ultimate strain to failure of the 
obturator material. The sabot components are already segmented so no 
additional breaking of materials is required, and the tangential spin 
velocities result in fractured obturator and segmented sabot components 
flying free of the rod penetrator. The fin stabilized sub-caliber rod 
penetrator is now free to fly undisturbed towards its target. 
Conclusions, Ramifications, and Scope of Invention 
The projectile of the invention provides an improved, highly efficient, low 
mass-energy loss discarding sabot of high in-bore stability and high 
trajectory accuracy, for a superior sub-caliber armor penetrating rod with 
simplified component assemblies, for use in small caliber gun systems. 
It is intended that my invention be utilized in a wide range of small 
caliber guns of bore diameter less than or equal to 25 millimeters, for 
which it is a more efficient armor piercing projectile design. While my 
above description contains many preferred specificities, these should not 
be construed as limitations on the scope of the invention, but rather as 
an exemplification of one preferred embodiment thereof. For example, the 
threaded or grooved interface between the sabot and the rod penetrator can 
have more or less grooves or threads of different pitch, depth and form. 
The sabot can be segmented longitudinally into two, three, or more equal 
parts. The sabot material can be aluminum alloy or lower density magnesium 
alloy depending on the gun system used. The penetrator may be of steel, 
tungsten alloy or depleted uranium alloy depending on the gun system and 
the targets under consideration. The one piece solid obturator can be of 
different length depending on the projectile caliber and can have more or 
less of a pressurized obturator cavity depending on the barrel pressures 
of the gun system under consideration. The fin stabilization can be 
exchanged with a cone stabilizer depending on the launch velocity of the 
gun system under consideration. A cone or flare stabilizer is a conical 
tapered appendage which provides unique stability characteristics 
depending on flight Mach number. The use of the boattail may not 
necessarily be required, depending on the caliber of the projectile under 
consideration, and the desired aerodynamic performance characteristics. 
The interference press fit connection between the fin appendage and the 
rod penetrator may also be substituted with a threaded connection, 
depending on the caliber of the projectile and the cost of suitable 
manufacturing processes. The use of the tracer cavity in the rod 
penetrator and the fin appendage is optional, depending on the desired 
performance characteristics of the cartridge and whether a trajectory 
trace is desired. The nose of the penetrator rod can have a different 
aerodynamic contour, from tangent ogive to straight cone, depending on the 
desired aerodynamics of the flight projectile. Other streamlining aspects 
of the rod penetrator can also be modified as required by the gun system 
application. The segmented structural sabot bulkhead does not always need 
to be located between two equal length sabot ramps. The front and aft 
ramps may be of different length and contour. This contour may be concave, 
a series of one or more straight sections, or convex, depending on the 
unique requirements of the cartridge and weapon system. However, the 
preferred embodiments of concave and equal length sabot forward and aft 
ramps yields the minimum weight and maximum structural performance 
combination. 
Efficient armor piercing projectile design involves a careful balance of 
many gun and armor target parameters, which are unique to each system 
under consideration. Nevertheless, certain critical design practices apply 
across the boundaries of small caliber gun systems. These practices 
include the need to incorporate a tracer cavity of adequate diameter and 
depth for the eye to track the trajectory of the sub-caliber projectile; 
the tracer cavity cannot detract from the armor penetrating potential of 
the rod penetrator; the segmented sabot weight is minimized for its 
in-bore stability and structural requirements; and the projectile 
obturation provides adequate propellant gas sealing and still separates 
cleanly from the rod projectile without introducing trajectory 
disturbances, once free from the barrel. 
To accomplish these requirements in small caliber projectiles, the rod 
penetrator is made longer to accommodate the tracer cavity so that removal 
of high density or high strength armor penetrating material is 
unnecessary. Making the rod longer to accommodate the tracer cavity 
requires that the rod penetrator be fin stabilized. Minimizing the 
segmented structural sabot weight requires a sabot design which is of 
length less than its bulkhead diameter, and has forward and aft sabot 
ramps which are concave and of substantially equal length. Clean 
separation of the projectile obturator upon muzzle exit requires that the 
obturator components be designed with specific attention to the unique 
structural and mechanical characteristics of candidate materials. 
Different classes of obturator materials perform better depending on the 
obturator design and projectile assembly. Reducing the cost of 
manufacturing, assembly, and inspection of high quality discarding sabot 
projectiles depends on developing designs utilizing a minimum number of 
components and processes, and simplifying obturator design greatly reduces 
the manufacturing costs of discarding sabot ammunition. The invention is 
the embodiment of these design practices for armor piercing projectiles 
for use in small caliber gun systems.