Abstract:
A piece of small arms ammunition includes a jacket bullet of an aerodynamically optimized configuration having a profile, with the exception of its ends and of an attachment section, which is drag optimized in accordance with a relation derived from the known Haack equation. The range probable error of the ammunition is further additionally and advantageously affected by the design of the head and tail end of the bullet.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to small arms ammunition comprising a cartridge case adapted to contain a powder charge and having an open end, a closed end and a logitudinal axis, a percussion cap substantially centered at said closed end and a rotationally symmetric jacket bullet enclosing a metallic core located at said open end. The invention, also, relates to a jacket bullet of the kind just mentioned. 
     For clarification, the term &#34;small arms&#34; in this context relates to subcaliber arms having a caliber below 0.5 in (12.7 mm) and particularly to a caliber in the range of 0.17 to 0.25 in (4 to 6.35 mm). 
     A rotationally symmetric jacket bullet is known from a publication by the US Department of Commerce, National Technical Information Service, No. AD-A025 131 (Michael Pino, &#34;The effect of varying certain parameters on the performance of the S.C.A.M.P. produced 5.56 mm projectile&#34;, DARCOM Intern Training Center, May 1976). The known bullet has an ogive-shaped profiled portion, a cylindrical central portion and a frustroconically-shaped rear portion. It is at first stated in the report (see page 3, para 2, lines 4 to 5) that &#34;more specifically there is no published material on the effects of ogive, nose radius, or boattail, or spin rate&#34;. The profiled portion may be shaped parabolically, conically or spherically (1.c, page 24), however, said profiled portion is stated to require a change in rifle design if changed (see page 9, lines 2 to 4: &#34;The ogive cannot be changed because of the effect of necessitating a complete redesign of the rifle.&#34;) Correspondingly the author of this report restricts himself to the effects produced by variations in the shape of the head and/or in the shape of the tail on the bullet performance. 
     In a paper presented at the International Symposium on Small Arms, Aberdeen, USA, in October 1979, by Beat Kneubuhl of the Armament Technology and Procurement Group, Ministry of Defense, Switzerland, the optimation of shapes for small arms bullets, in particular of the profiled portion in jacket bullets for small arms ammunition with respect to drag is reported. Starting point in the optimation is a mathematical formula developed by Haack for a projectile shape of minimum drag applicable to large-caliber projectiles having muzzle velocities in the supersonic range (Oerlikon Taschenbuch, Werkzeugmaschinenfabrik Oerlikon-Buhrle AG, Zurich, Schweiz, May 1981, Chapter 5.2.3., page 168 to 171). A parameter equation is derived therefrom for the calculation of an optimal shape with respect to drag for the profiled portion of the small arms bullet as mentioned. 
     SUMMAY OF THE INVENTION 
     It is one object to be achieved by the invention to provide for small arms ammunition or a jacket bullet therefor of the initially mentioned kind which has an improved hit probability. 
     It is an object to be achieved by the invention to provide for small arms ammunition or a jacket bullet therefor of the initially mentioned kind which also has improved flight properties. 
     It is a further object to be achieved by the invention to provide for a jacket bullet for small arms ammunition of the kind mentioned initially which has an increased ballistic final impact energy. 
     It is another object to be achieved by the invention to provide for a jacket bullet for small arms ammunition of the kind mentioned initially which has an increased velocity of flight. 
     It is also an object to be achieved by the invention to provide for a jacket bullet for small arms ammunition of the kind mentioned initially which shows lower crosswind deflection. 
     Furthermore, it is an object to be achieved by the invention to provide for a jacket bullet for small arms ammunition of the kind mentioned initially the shape of which results in a minimized forebody drag without impairing the ballistic final impact energy. 
     Also, it is an object to be achieved by the invention to provide for a jacket bullet for small arms ammunition of the kind mentioned initially which has improved flight properties and which can be manufactured as simply as possible in large numbers. 
     It is a final object to be achieved by the invention to provide for small arms ammunition and a jacket bullet therefor of the initially mentioned kind which is readily exchanged for the presently available ammunition without requiring any rifle redesign, particularly in respect of spin rate. 
     The invention is based on the surprising recognition that, contrary to expectation, an aerodynamic design of small arms ammunition and of the small-caliber jacket bullets used therein affects the hit probability for such bullets to a very significant degree despite the small size, the relatively short range and the relatively short flight time typical therefor. 
     According to the invention said objects are achieved in small arms ammunition and in jacket bullets of the initially mentioned kind by the bullet being shaped so as to be aerodynamically optimized in respect of drag and being provided, with the exception of said opposed ends and said attachment section, with a profile which is determined solely by a continuous function r(x) having a finite value of the continuous differential quotient (dr/dx); said profile of the jacket bullet having an imaginary tip which is spaced by a distance --s from the origin of a rectangular coordinate system, the positive x-axis of which represents a jacket bullet axis of symmetry and the y-axis of which represents a direction of the bullet radius r, while a real tip of said bullet is located at the origin of said coordinate system. The profile of the bullet is determined, with the exception of said opposed ends and said attachment section for the cartridge case, by a sum function 
     
         r(x)=r.sub.1 (x.sub.1)+r.sub.2 (x.sub.2) 
    
     in which the range of x 1  is defined by 
     
         x.sub.1 =(h/2)(1-cos a)-(s/2)(1+cos a), 
    
     h representing an imaginary length of said bullet from x 1  as determined by a=π to the imaginary tip of said bullet and arc cos (h-s)/(h+s)≦a≦π, while the associated values of r 1  are given by ##EQU1## wherein arc cos (h-s)/(h+s)≦a≦π, and in which the range of x 2  is defined by 
     
         x.sub.2 &gt;h, 
    
     with r 2  =constant=r 0  (maximum radius of the bullet) 
     Advantageously, the jacket bullet according to the invention is manufactured from plated alloyed steel by deep drawing. 
     The amount of the distance -s in the jacket bullet according to the invention is in the range of 0.1 to 0.5 r 0  ; such design of the head of the jacket bullet is expedient since well-defined turbulences are generated thereby which preclude instabilities due to exlusive laminar flow. The location of the attachment region for the cartridge case is such that a small section of the cylindrical portion projects from the cartridge case when the same is attached to the bullet according to the invention which results in improved guidance. Conveniently, a two-part frustroconical portion forms the rear portion of the jacket bullet according to the invention whereby the stability and the flight properties of the bullet are favourably affected additionally. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages achieved by the invention will become apparent and the invention will become better understood by the subsequent description of specific embodiments of the invention with reference to the annexed drawings wherein 
     FIG. 1 represents a longitudinal section of a piece of small arms according to the invention; 
     FIG. 2 shows a longitudinal section at an enlarged scale of a first embodiment of a jacket bullet for small arms ammunition according to the invention; and 
     FIG. 3 shows a longitudinal section at an enlarged scale of a second embodiment of a jacket bullet for small arms ammunition according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a longitudinal section of a piece of ammunition having a caliber of 0.223 Rem (5.56 mm) which is a conventional type of small arms ammunition. The piece comprises a conventional cartridge case 1 made of brass which contains a powder charge 2 of conventional composition like, for example, a small arms smokeless powder and further comprises a jacket bullet 3 attached thereto. The jacket thereof is made of a material conventionally used therefor like plated alloyed steel or nonferrous metal rich in copper and encloses a core 27 made of a material conventionally used therefor like lead or a lead alloy, but may also be made of steel or of sintered material. The jacket bullet 3 comprises a front portion 4 which is aerodynamically optimized in shape to minimize drag as described in detail hereinbelow, a substantially cylindrical central portion 5 and a generally frustroconicallyshaped rear portion 6. The central portion 5 has a groove 7 instead of which the central portion 5 may also be knurled for attachment of a rim 9 of an open end 8 of cartridge case 1. The cylindrical portion 5 extends outwardly from the attachment section by 0.01 in (0.254 mm) which is the equivalent of about 0.1 r 0  with r 0  representing the radius of the cylindrical central portion 5 i.e., the maximum bullet radius. The extension may measure anywhere in the range of 0.1 to 0.5 r 0 . The remaining portion thereof and the rear portion 6 are enclosed in cartridge case 1. A percussion cap 11 is placed into the closed end 10 of the cartridge case 1 and is centered with respect to the longitudinal axis of the same. 
     The aforementioned jacket bullet is illustrated in greater detail and at an enlarged scale in FIG. 2 in longitudinal section; the jacket bullet thus shown is of a rotationally symmetric shape optimized aerodynamically in respect of drag. The jacket bullet comprises a front portion 20 having a blunted front end 21 of solid material, a cylindrical central portion 22 including a groove 23, a rear portion 24 including two frustroconical sections 25 and 26 and a bullet core 27. 
     The jacket bullet has a profile determined by the parameter equation given further below which is derived in standard steps from the initially mentioned Haack equation relating to the minimum drag shape of large-calibre projectiles (expressed in terms of the drag coefficient c D ). In FIG. 2 the real front end of the jacket bullet is shown to be located in the origin of a rectangular coordinate system so that the height of the bullet extends along the positive x-axis in the coordinate system, while the radius thereof extends in the y-direction. Excepting the front end 21, the groove 23 and the rear portion 24, the profile of the jacket bullet is represented by a continuous function r(x) having a finite value of the associated continuous differential quotient (dr/dx). This function represents a sum function 
     
         r(x)=r.sub.1 (x.sub.1)+r.sub.2 (x.sub.2) 
    
     encompassing a range r 1  (x 1 ) associated with a continuously decreasing differential quotient and a range r 2  (x 2 ) in which the differential quotient is constant and equal to zero and extending towards an imaginary tip displaced by --s from the origin of the coordinate system. 
     In starting from the Haack equation (1.c.) for x the parameter equation 
     
         x.sub.1 =(h/2)(1-cos a)-(s/2)(1+cos a) 
    
     is obtained for the first member of the sum function as above. Therein h is the imaginary bullet height extending from a=π to the imaginary tip, s is the displacement of the real front end 21 from the imaginary tip and &#34;a&#34; is a parameter which may assume any value in the range from arc cos (h-s)/(h+s) to π. From the further Haack equation (1.c.) the following parameter equation for r ##EQU2## is readily obtained for the first member of the sum function as above. Therein r 0  is the radius of the cylindrical portion 22 of the jacket bullet, r 1  is the radius of the jacket bullet in the range of x 1  and arc cos (h-s)/(h+s)≦a≦π. The second member in the sum function as above relates to the range x 2  &gt;h and is defined by 
     
         r.sub.2 (x.sub.2)=constant=r.sub.0. 
    
     As will be readily evident, the profile determined by the aforementioned sum function is distinguished by an absolutely continuous transition between the ranges of x 1  and x 2  since in the case of a=π the values of r 1  and r 2  become identical. 
     In the embodiment as shown, the value of s is 0.025 in (0.65 mm) or, respectively, 0.232 units of the bullet radius r 0  but may have any value in the range of 0.1 to 0.5 r 0 . The front end 21 provides for a well-defined turbulence at the tip of the projectile during flight so that instabilities due to a substantially laminar flow are avoided. The cylindrical central portion 22 corresponding to the range of x 2  in the formula as given above has a groove 23 for attachment of a cartridge case as shown in FIG. 1. The groove 23 may be replaced by a knurled section as described above with reference to FIG. 1. In the embodiment as shown the cylindrical portion extends beyond the groove 23 by a section 22a having an axial length of 0.01 in (0.254 mm) or respectively, of about 0.1 unit of the bullet radius r 0  but may assume any value in the range of 0.1 to 0.5 r 0 . At the end remote from the front portion 20 the central portion 22 is followed by the rear portion 24 comprising two substantially frustroconical sections 25 and 26. The interior section 25 has a cone angle of 8 degrees in this embodiment which may have any value in the range of 5 to 10 degrees; it has a length of 0.07 in (1.82 mm) corresponding to 0.65 units of the bullet radius r 0 . The exterior section 26 has a cone angle of 60 degrees but may have any other value approximate thereto; it terminates at a distance from the symmetry axis. The aforementioned cone angles each have an imaginary apex located on an imaginary extension of the symmetry axis outside the bullet. The particular shape of the rear portion 24 assists in the effect of the specific profile on the flight properties of the projectile by favourably affecting the stability and the drag response. 
     The jacket bullet as described hereinbefore encloses a core made of lead or a lead alloy or any other conventional material like steel or sintered material. 
     FIG. 3 shows a particularly preferred embodiment of the jacket bullet according to the invention in a drawing of the same kind as FIG. 2. There are recognized therein a profiled front portion 30 including a front end 31, a cylindrical central portion 32 including a groove 33 for attachment of a cartridge case, a rear portion 34 comprising two substantially frustroconical sections 35 and 36 and a core 37. While the jacket bullet shown in FIG. 3 is practically identical with the one shown in FIG. 2 with respect to material composition and in most dimensional aspects, the significant difference is in the interior frustroconical section 35 which has a cone angle of only 7 degrees and a length of 0.13 in (3.6 mm) or, respectively, of 1.3 units of the bullet radius r 0 . 
     The small arms ammunition and the jacket bullet according to the invention as described hereinbefore are distinguished by having, contrary to expectation, very significant improvements in some important properties over those of the prior art ammunition and bullets of such kind in which the front portion is formed with an ogive, i.e. parabolically, conically or spherically. Of these properties the hit probability is the most important. In test firings this has been found to be considerably improved on; thus in the dispersion pattern the spread in the horizontal and in the vertical axis of the dispersion pattern proved to be better by 30 and 60 percent, respectively, at a firing range of 30 to 300 meters. 
     The following table gives data for some other important properties of a prior art conventional ammunition having a caliber of 0.223 Rem (5.56 mm) and the corresponding values obtained for ammunition according to the invention of the same caliber; also listed are the relative changes in the data in percent of the respective values as obtained with the prior art ammunition. 
     
                       TABLE______________________________________Comparison of Absolute and Relative Test Data for the Prior ArtJacket Bullet and for the Jacket Bullet According to theInvention at Different Firing Ranges        Jacket Bullet              Acc. to Invention      Firing  Prior Art         RelativeTest       Range   Absolute  Absolute                                (percent)______________________________________Vertex Height      300 m   0.19 m    0.19 m  0      500 m   0.73 m    0.66 m  -10Flight Time      300 m   0.39 sec. 0.39 sec.                                0      500 m   0.76 sec. 0.74 sec.                                -3Ballistic  300 m   706 J     879 J   +25Final Impact      500 m   357 J     525 J   +47EnergyCrosswind  300 m   0.78 m    0.59 m  -24Deflection 500 m   2.39 m    1.87 m  -22______________________________________ 
    
     As will be a apparent from the table the jacket bullet which is aerodynamically optimized in shape with respect to drag according to the invention has a relatively less steep trajectory of flight and a somewhat smaller time of flight and, particularly at high firing ranges, a significantly higher ballistic final energy of impact. The crosswind deflection is reduced by the high amount of 25 percent at all firing ranges investigated although the projectile according to the invention has a higher weight and a lower muzzle velocity as compared to the corresponding data of the prior art projectile. 
     The data given in the table were determined in the usual manner by utilizing a known light barrier method to obtain the drag coefficient and by known calculations from the drag coefficient thus obtained. 
     The small arms ammunition including the jacket bullet as described hereinbefore has the particular advantage of being compatible with most of the important rifle designs presently in use. Contrary to the expectation explicitly expressed in the first mentioned prior publication the new jacket bullet profile does not require any changes in rifle design for its use.