Method of making spin stabilized discarding sabot projectile

A method of manufacturing a spin stabilized discarding sabot projectile comprising the steps of preassembling a subcalibre cylindrical projectile in a full calibre cylindrical pusher, installing the subassembly in a two section injection molding machine with spring biased pusher locator and spring biased projectile nose locator for precisely holding the subassembly aligned with a primary axis, following which plastic material is injection molded about the projectile. Surplus plastic material may be removed as by machining and a noise piece may be added.

BACKGROUND OF THE INVENTION 
Spin stabilized discarding sabot projectiles are well known in the field of 
ordnance. By definition a discarding sabot projectile comprises in part a 
subcalibre core or projectile coacting with a full calibre pusher. The 
full calibre pusher coacts with a rifled barrel of a gun firing the 
projectile; the expanding gases caused by the detonation of a charge 
imparting a relatively high velocity and spin to the assembled pusher and 
subcalibre core. After discharge from the muzzle of the gun the sabot is 
discarded and the subcalibre core/projectile separates from the pusher and 
continues along its ballistic path, the subcalibre core having a much 
higher impact velocity (at least theoretically) than would be the case for 
a full calibre round. 
Substantial efforts have been devoted in the past to improve the hitting 
accuracy of the subcalibre projectile. Hitting accuracy is adversely 
affected by nonaxial dispersing forces and moments affecting the 
subcalibre projectile during the critical separation from the pusher and 
during the separation of the discarding sabot components. All known prior 
arrangements for producing a discarding sabot projectile have one or more 
disadvantages, i.e., fail to yield a projectile with a low dispersion 
factor that can be made on low cost mass production basis. 
An object of the present invention is to provide a new and significantly 
improved method for producing a low dispersion spin stabilized discarding 
sabot projectile. 
This application also discloses a unique spin stabilized discarding sabot 
projectile which is the subject matter of our copending application filed 
concurrently herewith. 
SUMMARY OF THE INVENTION 
Our invention provides a method of producing a low dispersion discarding 
sabot projectile comprising the steps of: 
(a) preassembling a subcalibre cylindrical projectile and a full calibre 
cylindrical pusher so that a rear portion of said subcalibre projectile is 
concentrically set into a cup-like central forward facing recess in said 
pusher, said pusher comprising in part a circumferential rotation groove 
positioned in approximate radial register with said rear portion of said 
projectile; 
(b) placing said preassembled concentric subcalibre projectile and pusher 
into a two-section injection molding machine with a first section of said 
molding machine including recessed means for receiving and positioning the 
rear portion of said pusher and with a second section of said molding 
machine having means for receiving and positioning a forward tip portion 
of said subcalibre projectile; 
(c) positioning said two-section molding machine so that said first and 
second sections are in abutting relationship and define a complex 
cylindrical cavity concentric with respect to a primary axis passing 
through (i) the center of said tip portion of said projectile and (ii) the 
center axis of said pusher; 
(d) injection of plastic material into said cavity which material, upon 
hardening, forms a discarding sabot adjacent said projectile and a 
rotation ring positioned in said circumferential groove; 
(e) removing, as by machining, surplus hardened plastic material from the 
external surfaces of said discarding sabot and said rotating ring, said 
machining being done with respect to a said primary axis; and 
(f) installing a preformed nose piece on said pointed forward tip portion 
of said subcalibre projectile.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, reference numeral 25 generally designates a subcalibre 
projectile shown to be a complex cylindrical form with a main body portion 
26, a tapered rear portion 27 (sometimes referred to as a boat tail 
shape), a tapered forward portion 28 and a pointed forward tip portion 
comprising a shoulder portion 29, a straight portion 30, and a final 
pointed tip 31. A suitable material for projectile 25 is tungsten. 
Reference numeral 40 generally designates a pusher also having a complex 
cylindrical shape. Pusher 40 is preferably made out of a strong, 
lightweight metal such as aluminum. A cup-like centrally located stepped 
diameter forward facing recess 41 has an end wall 42 and has an aft 
diameter 35 selected to receive the tapered end portion 27 as well as a 
small part of the full body section 26 of the subcalibre projectile 25. 
The forward portion of recess 41 is identified by reference numeral 35; 
this portion of the recess has a slightly larger diameter than the rear 
portion 35. (Shown only in FIG. 1). As indicated above, the step between 
portions 35 and 36 is longitudinally selected so that when the subcalibre 
projectile 25 is fitted into the pusher (as in FIG. 2) a small 
longitudinal portion of the portion 26 of projectile 25 sits into the 
smaller diameter portion 35. The diameters 35 and 26 are selected so that 
a close fit is provided. This arrangement accurately locates the 
subcalibre projectile coaxially with the pusher 40. Typical dimensions for 
diameters 35, 36 and 26 are 0.710+0.001; 0.713+0.001; and 0.707-0.002 
inches respectively. A typical insertion of diameter 26 into the reduced 
diameter portion 35 of recess 41 is in the range of 0.041 to 0.111 inches. 
The larger diameter portion 36 provides clearance to allow air to vent 
into the rear portion of recess 41 behind the subcalibre projectile 25 
during separation; this additional clearance is also advantageous because 
it permits limited angular movement between the pusher and subcalibre 
projectile during separation without causing binding or perturbation of 
the flight of the subcalibre projectile. Various means not shown but known 
to those skilled in the art may be utilized for imparting rotation from 
the pusher as it accelerates down the gun barrel to the subcalibre 
projectile 25. The external surface of pusher 40 is a complex cylindrical 
one comprising separate surfaces identifed in FIG. 1 by reference numerals 
43-48. Surface 43 is adjacent the forward end of pusher 40 and is of a 
relatively small diameter compared to the remainder of pusher 40. Next aft 
is a rotation ring channel 44. Next aft is an undulating portion 
identified by reference numerals 45, 46, and 47 to provide a means for 
attachment of the pusher/projectile to a metallic shell casing not shown. 
Next aft is a straight portion 48 which extends from the aft or rear part 
of the pusher forward to the undulating section 46. A conically shaped 
recess 49 is provided in the rear face or end surface of the pusher 40; 
this conically shaped surface has great utility with respect to the 
accurate positioning of the pusher within the injection molding machine to 
be described below. Further, it permits the saving of some weight in the 
overall weight of the pusher to thus provide increased velocity for the 
overall projectile. 
Also depicted in FIG. 1 is a preformed nose piece 55 having a tip 57 and a 
recessed portion identified by reference numerals 58, 59, and 60 which are 
respectively intended to mate with surfaces 29, 30 and 31 on the tip of 
projectile 25. Nose piece 55 may be preformed out of a suitable polymer 
material. 
In FIG. 1 reference numeral 50 designates an axis passing through the 
center of the tip portion of the projectile, (and thus the center axis of 
the projectile), the center axis of the pusher 40, and the center axis of 
the nose piece 55. 
In FIG. 2 the subcalibre projectile 25 and pusher 40 are shown in 
preassembled form. Here it will be noted that the entire boat tail or rear 
tapered portion 27 of the subcalibre projectile is within the recess 41 
together with a portion of the right cylindrical main body portion 26. As 
indicated above, the coaction between the reduced diameter portion 35 of 
recess 41 and portion 26 tends to provide a self-alignment between the 
axes of pusher 40 and subcalibre projectile 25. 
Referring to FIGS. 3 and 4 the injection molding apparatus is depicted; it 
may be described as a two-section molding machine having a first section 
60 with an end face 61 and a second section 80 with an end face 81, the 
apparatus as depicted in FIG. 4 being shown with the two sections in 
abutting relationship, i.e., with surfaces 61 and 81 abutting one another. 
The first section 60 comprises a recess 62 adapted to receive the full rear 
half of the pusher 40. At the bottom of the recess 62 is an end surface 63 
which in turn has a central bore 64 or recess in which is positioned the 
shaft portion 66 of an axially displaceable pusher locator 67 having a 
relatively large diameter convex end face more specifically identified as 
a conically shaped face extending forward into the recess 62 and adapted 
to mate with the conically shaped or concave recess 49 in the pusher 40. A 
spring 69 is positioned between the end of shaft portion 66 and the end 65 
of bore 64 so as to spring bias the locator 67 to the right as depicted in 
FIG. 4. 
An appropriate port means 82 are provided between the section 60 and 80 so 
as to provide a gate for injection of plastic material. The second section 
of the injection molding machine has a substantial cavity 83 by comprising 
a first portion 84 extending from surface 81 in a direction generally 
parallel to the primary axis 50 to a point in radial register with the 
junction between surfaces 26 and 28 on the subcalibre projectile 25; at 
this point the shape of the mold is beveled at an angle to axis 50 
represented by reference numeral 85 and terminating in a section 86 which 
is perpendicular to the primary axis 50. Means are provided in the second 
section 80 for receiving and positioning the forward tip portion of the 
subcalibre projectile; more specifically these means include a spring 
biased axially displaceable plunger member 89 which is adapted to move 
axially along primary axis 50 within a recess 87. An appropriate spring 
means 96 is provided between one end of the member 89 and the end surface 
88 of the recess 87, the spring means 96 tending to displace the member 89 
to the left as shown in FIG. 4. At the other end of the receiving end of 
the positioning means is a complex recess having surfaces 91, 92, and 93 
adapted to mate with respectively the surfaces 29, 30 and 31 of the 
subcalibre projectile. Due to the substantial axial extent of the portion 
30 on the subcalibre projectile and its coacting cooperating surface 92 in 
the positioning and receiving means it will be understood that the forward 
tip of the subcalibre projectile is held in alignment with the primary 
axis 50. Because the rear portion of section 26 of the projectile 25 is 
closely held by portion 35 of pusher 40, the entire projectile 25 is in 
alignment with the primary axis 50. 
A plurality of knife edge means 101, 102, 103, and 104 shown best in FIG. 3 
extend from member 80 toward the subcalibre projectile and have the 
function of providing weakened slots in the final discardable sabot, in 
this regard see slots 102A and 104A in FIG. 5. 
It is thus seen that the preassembled pusher and subcalibre projectile are 
held within the injection molding machine by the pusher plug locator 67 
and the subcalibre projectile nose locator 89. In this manner, as 
described above, the extremely critical result of having the axes of the 
subcalibre projectile and the pusher in alignment with the primary axis 50 
is accomplished. This in combination with the utilization of the primary 
axis for purposes of molding the discarding sabot and the machining of the 
discarding sabot will assure an an extremely low dispersion rate, i.e., 
high firing accuracy for the projectile. A suitable polymer may be used 
for the injection molding of the discardable sabot. 
FIG. 5 depicts the projectile upon removal from the molding machine. A 
number of reference numerals have been allocated to various portions of 
the injection molded discarding sabot. At the forward end of the 
projectile the reference numeral 108 designates the forward face of the 
plastic, this would correspond to mating with the surface 86 in the mold. 
Slightly aft of surface 108 is a straight portion 109 with a cylindrical 
inside diameter, the outer contour being the bottoms of the weakened 
slots. Portion 109 continues to the junction between surfaces 28 and 29 on 
the subcalibre projectile 25. Further aft is a portion 110 lying adjacent 
to surface 28; further aft is a straight portion 111 lying adjacent to 
surface 26. Reference numeral 112 designates that portion of the 
discarding sabot that surrounds portion 43 of the pusher 40. Further 
reference numeral 114 designates the portion of the molded material which 
has been molded into the rotation ring groove 44 as shown in FIGS. 1 and 
2. 
The next step in the manufacture of the projectile is to machine away 
surplus material leaving a configuration as depicted in FIG. 6. In FIG. 6 
the reference numeral 113A designates the final diameter of the rotation 
ring and reference numerals 120, 121 and 122 depict the mid, forward, and 
rear external surfaces of the discarding sabot. The cost of the projectile 
may be reduced through the elimination of this machining step if the mold 
cavity is characterized so as to accommodate the varying amount of 
shrinkage of the plastic material caused by the variations in thickness of 
the plastic material such that the final shape and size after shrinkage 
will meet the design criteria. 
FIG. 7 shows the projectile in the form of FIG. 6 together with the nose 
piece 55 which has been added and bonded to the projectile with 
appropriate bonding means. The reference numeral 130 depicts a gap between 
the external surface of the nose piece 55 and the portion 109 of the 
discarding sabot. This gap has significance in assisting the breaking away 
of the sabot from the projectile as the projectile exits from the gun 
barrel. In this regard refer to FIG. 8 wherein the projectile is shown 
emerging from the gun barrel 140. Parenthetically it will be noted that 
the principal internal diameter of the gun barrel is identified by 
reference numeral 142; this corresponds with the diameter 48 on the pusher 
40. The rifling rings have a larger diameter 141 and it will be noted that 
the rotation ring 113A is adapted to be the same as the diameter 141. When 
the sabot portion of the projectile exits the end or muzzle of the gun the 
polymer sabot fractures along the grooves 101A-104A and the sabot pieces 
are discarded by the effects of the projectile spin. The pusher is pulled 
rearward (relatively away from the subcalibre core 25 because of 
aerodynamic, i.e., drag, forces. In FIG. 8 the sabot has begun the 
separation process beginning with the nose of the projectile. In FIG. 8 
the reference numerals 109, 110, and 111 are depicted and may be compared 
with the corresponding numbers as shown in FIG. 5. The two principal 
elements of the sabot depicted in FIG. 8 are identified by reference 
numerals 150 and 152 respectively breaking away from the pusher at 
locations identified by reference numerals 151 and 153. Alternately, (as 
shown in FIG. 8A) the separation of the sabot elements may be adjacent the 
ring portion 43 of pusher 40 with the fracture line being approximately at 
the forward end of the rotation ring 113A; in this regard see FIG. 9. 
FIG. 9 shows the subcalibre projectile 25 with its associated nose piece 55 
fully separated from the pusher 40 and on its way toward its target. The 
pusher 40 is depicted to include the rotation ring 113A traversed by a 
plurality of rifling rings 113AA. 
While we have described a preferred embodiment of our invention, it will be 
understood that the invention is limited only by the scope of the 
following claims.