Patent Publication Number: US-11035653-B2

Title: Metal cartridge for ammunition and method of making it

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2019/053630, filed Feb. 14, 2019, which claims priority of Italian Patent Application No. 102018000003077, filed Feb. 27, 2018. The entire contents of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a metal cartridge for ammunition, particularly for artillery or antiaircraft or antitank rifles. 
     BACKGROUND 
     A cartridge of this type is generally made up of a front retaining collar for retaining a projectile and a hollow body having a rim at the rear provided with a central primer hole and at the front a shoulder connecting to the collar. 
     The hollow body bounds a chamber of the propellent necessary for the ejection of the projectile. 
     A traditional cartridge for ammunition is generally made in a single piece of brass by deep drawn stamping via a transfer press. 
     A traditional cartridge for ammunition has some disadvantages, including weight, which complicates logistics by limiting the quantities that can be transported in a single lot, especially in the case of air transport. 
     Moreover, the stamping of the cartridge has some intrinsic technological limits tied to the opening of the punch and die cavity which penalize the internal volume obtainable for the chamber of the propellent. 
     SUMMARY 
     The technical task of the present invention is therefore to provide a metal cartridge for ammunition that enables the aforesaid technical drawbacks of the prior art to be overcome. 
     Within the scope of this technical task, one object of the invention is to provide a metal cartridge for ammunition which has a chamber of the propellent with an increased volume, the caliber being equal. 
     Another object of the invention is to provide a metal cartridge for ammunition which ensures an increased range of the projectile, the caliber being equal. 
     Another object of the invention is to provide a metal cartridge for ammunition which has a reduced weight, the caliber being equal. 
     The technical task, as well as these and other objects, are achieved, according to the present invention, by providing a metal cartridge for ammunition having a front retaining collar for retaining a projectile and a hollow body having a rim at the rear provided with a central primer hole and at the front a shoulder connecting to said collar, said hollow body having an internal surface that bounds a chamber of the propellent, characterized in that it is formed by a rear element and a front element that are structurally independent, fixed stiffly to one another, and in that said internal surface has at said rim at least one notch configured to increase the volume of said chamber of the propellent. 
     The present invention also discloses a method of making a cartridge for ammunition, characterized in subjecting two light alloy rods to mechanical removal of chips so as to form said rear element of the cartridge and said front element of the cartridge. 
     Advantageously said two light alloy rods are machined internally and externally. 
     A solid rod is preferably used to form the rear element and an axially hollow rod to form the front element. 
     Advantageously, the mechanical removal of chips is designed to impart a greater volume to the chamber of the propellent compared to the starting caliber. 
     In particular, thanks to the mechanical removal of chips, a cartridge is made in which the collar has an internal diameter that is smaller than the internal diameter of the chamber of the propellent. 
     The reduction of material by removal of chips, besides increasing the internal volume of the chamber of the propellent, contributes to making the cartridge more lightweight, and this weight reduction effect is added to the one tied to the use of a light alloy, particularly of aluminum, which has the necessary mechanical properties. 
     The light Al alloy is preferably an alloy having Zn as the main alloying element, and Cu and Mg as other alloying elements. 
     An alloy used for aeronautical structures having, as alloying elements, Cu with a concentration of between 1.2 and 2.0% by weight, Mg with a concentration of between 2.1 and 2.9% by weight and Zn with a concentration between 5.1 and 6.1% by weight is preferably used. 
     In particular, use is made of a light alloy, ERGAL™ 7075, which has noteworthy mechanical characteristics, such as, for example, a “mechanical memory”, i.e. an elastic modulus, which, for example, the brass traditionally used for cartridges does not have. 
     An alloy of this type, in other words, returns more or less to the same dimensions as the original ones after firing, unlike brass. 
     On the other hand, though nearly all other minor aluminum alloys can be stamped like brass, they do not have a mechanical memory and remain deformed after firing, and are thus unusable after the first firing. 
     An alloy of this type, by contrast, functions like and better than brass, with about half of the weight for the same product. 
     According to the invention, light alloys of this type which cannot be stamped are machined by removal of chips, it being envisaged to form the cartridge from two pieces which are then securely coupled. 
     Other features of the present invention are also defined in the claims hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features and advantages of the invention will become more apparent from the description of a preferred but non-exclusive embodiment of the metal cartridge for ammunition according to the invention, illustrated by way of non-limiting example in the appended drawings, in which: 
         FIG. 1  shows a side elevation view of the cartridge, partially sectioned; 
         FIG. 2  shows a side elevation view of the rear element; 
         FIG. 3  shows a plan view of the rear element; 
         FIG. 4  shows an axial sectional view of the rear element; 
         FIG. 5  shows a side elevation view of the front element; 
         FIG. 6  shows a plan view of the front element; 
         FIG. 7  shows an axial sectional view of the front element. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     With reference to the above-mentioned figures, a metal cartridge for ammunition denoted in its entirety by the reference number  1  is shown. 
     The cartridge  1  can be used, in particular, for artillery or antiaircraft or anti-tank rifle ammunition. 
     The cartridge  1  has a front retaining collar  2  for retaining a projectile (not shown) and a hollow body  4 ,  10  having an internal surface that bounds a chamber  11  of the propellent. 
     The hollow body  4 ,  10  has a rim  5  at the rear provided with a central primer hole  6  and at the front a shoulder  3  connecting to the collar  2 . 
     The hollow body  4 ,  10  has a lateral wall that is thicker towards the rim  5 , in order to better withstand the pressure of the propellent, and thinner towards the collar  2 . The rim  5 , in turn, has a perimeter groove  7  externally that serves as a hold for the extractor. 
     Advantageously, the cartridge  1  is formed by a rear element  8  and a front element  9  that are structurally independent and fixed stiffly to one another. 
     Advantageously, in order to make the cartridge  1 , a light alloy is used, preferably an aluminum alloy, susceptible to mechanical removal of chips. 
     The rear element  8  has a lowered front end  8   a , on top of which there is a rear end  9   a  of the front element  9 . 
     The lowered front end  8   a  of the rear element  8  has an external thread  8   b  screwed to an internal counter-thread  9   b  of the rear end  9   a  of the front element  9 . 
     The rear element  8  includes the rim  5  and a rear portion  4  of the body  4 ,  10  in turn including the externally threaded front end  8   a.    
     The front element  9  includes instead the shoulder  2 , the collar  3  and a rear portion  10  of the body  4 ,  10  in turn including the internally counter-threaded rear end  9   a.    
     The rear portion  4  of the body  4 ,  10  and the front portion  10  of the body  4 ,  10  are juxtaposed flush with one another in the outer side of the junction part thereof. 
     The choice of forming the cartridge in two distinct and structurally independent parts increases the design choices for optimizing the internal volume of the chamber of the propellent  11 . 
     In this regard, the internal surface of the chamber of the propellent  11  advantageously has, at the rim  5 , at least one notch  12  configured to increase the volume of the chamber of the propellent  11 . 
     The notch  12  extends perimetrally to the central primer hole  6 . 
     In particular, the notch  12  extends longitudinally along a circumference having its center in the central primer hole  6 . 
     The notch  12 , finally, extends transversally along a semi-circumference that preferably has a diameter approximately equal to the diameter of the primer hole  6 . The inner side of the rim  5  can obviously have one or more recesses of another shape, size and position to increase the internal volume of the chamber of the propellent  11 . 
     Thanks to the possibility of making each element  8 ,  9  separately by mechanical removal of chips, the design options for increasing the internal volume of the chamber of the propellent  11  are considerably expanded. 
     For example, it is possible to shape the body  4 ,  10  with a cylindrical internal surface or a calibrated conicity even opposite the one typically adopted for the known cartridges to facilitate the extraction of the punch from the die. 
     The thickness of the wall of the cartridge  1  is controlled by grinding both the internal surface and external surface thereof. 
     In the case illustrated, the thinning of the wall of the body  4 ,  10  in the direction that goes from the rim  5  to the shoulder  3  is obtained by forming the body  4 ,  10  with a cylindrical internal surface  4   a ,  10   a  and a slightly conical external surface  4   b ,  10   b , for example with a conicity of 1°. 
     However, it is not excluded that, as noted, the internal surface  4   a ,  10   a  of the body  4 ,  10  may have in turn a conical conformation, so that the inner lumen of the body  4 ,  10  widens progressively in the axial direction that goes from the shoulder  3  to the rim  5 . 
     Moreover, it is not excluded that, as noted, the internal surface  4   a ,  10   a  of the body  4 ,  10  may have in part a cylindrical conformation and in part a conical conformation so that only for a certain length of the body  4 ,  10 , the inner lumen of the body  4 ,  10  widens progressively in the axial direction that goes from the shoulder  3  to the rim  5 . 
     In particular, the internal surface  4   a  of the rear portion  4  of the body  4 ,  10  can have a cylindrical conformation and the internal surface of the front portion  10  of the body  4 ,  10  can have a conical conformation or vice-versa. 
     As noted, the cartridge  1  is produced by mechanical removal of chips. 
     In particular, use is made of a solid light alloy rod which is machined on a lathe to form the rear element  8  of the cartridge  1  and an axially hollow light alloy rod, preferably made of the same material, which is machined on a lathe to form the front element  9  of the cartridge  1 . 
     The rods are subjected to an initial rough machining to remove most of the excess metal followed by finishing to obtain a final surface with the desired properties. 
     The light alloy used, in addition to being susceptible to mechanical removal of chips, must have the necessary mechanical and chemical characteristics. 
     For this reason, an aluminum alloy, ERGAL™, has been adopted as the preferred choice, in particular a light alloy ERGAL™ 7075 used in aeronautics, which exhibits excellent characteristics of mechanical strength and resistance to attack by acids, solvents and lubricants combined with an exceptional machinability by removal of chips. 
     Mechanical removal of chips is preferably performed on a sliding head lathe. 
     In order to produce the rear element  8 , the solid rod is internally and externally machined so as to form both the rear portion  4  of the body  4 ,  10  with the lowered front end  4   a  and the rim  5  with the primer hole  6 , the internal notch  12  and the external perimeter groove  7 . 
     In order to produce the front element  9 , the hollow rod is internally and externally machined so as to form both the front portion  10  of the body  4 ,  10 , and the shoulder  3  as well as the collar  2 . 
     The cartridge for ammunition and the method of making it thus conceived are susceptible to numerous modifications and variants, all falling within the scope of the inventive concept; moreover, all details may be replaced with technically equivalent elements. 
     The materials used, as well as the dimensions, may in practice be of any type, according to needs and the state of the art.