Abstract:
An ammunition cartridge having a bullet with a curved front end terminating in a flat nose normal to the longitudinal axis of the bullet and a casing attached to the rear end of the bullet is disclosed. The nose is provided with a centrally disposed projection and a reservoir of lubricant around the projection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This Application is a U.S. National filing under §371 of International Application No. PCT/GB02/00057, filed 9 Jan. 2002, claiming priority from British Appln. No. 0100578.4, filed 9 Jan. 2001, now pending (which is hereby incorporated by reference). 

   FIELD OF THE INVENTION 
   This invention relates to ammunition cartridges. It is particularly concerned with target and sporting ammunition, especially rimfire .22 ammunition, and will be more specifically described below with reference to .22 ammunition cartridges, although it will be appreciated that it is not intended to be limited thereto. 
   BACKGROUND OF THE INVENTION 
   Conventionally, .22 rimfire ammunition cartridges comprise a cylindrical casing closed at one end and open at the other, the open end being crimped to a bullet, usually of lead. The closed end or head of the casing defines an annular flange or rim containing a priming composition which ignites by a rimfire strike and the hollow body of the casing contains a propellant which is fired by the ignition of the primer causing rapid expansion of hot gases to force the bullet from its seating. 
   The bullet conventionally has a cylindrical body portion, which may be solid or hollow and a tapered, curved, or so-called ogive, portion leading from the cylindrical body to the nose of the bullet. The body portion usually has external knurls to hold lubricant which is provided to prevent material being stripped from the circumference of the bullet as it is expelled along the barrel of the gun. 
   It has previously been proposed, see for example, U.S. Pat. No. 3,866,536, to provide a flat nose on a bullet so that the ogive curve is in effect shortened and cut off at the nose end. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide an improved bullet shape to provide greater accuracy and consistency. 
   Accordingly, in one aspect, the invention provides an ammunition cartridge comprising a casing attached to a bullet, the bullet having a body portion of generally cylindrical shape, one end of which is attached to the casing and the other end of which has a tapering curved portion, the curved portion ending in a flat nose normal to the longitudinal axis of the bullet and the flat nose having a centrally-disposed projection in the direction of the longitudinal axis. 
   In another aspect the invention also provides a bullet having the shape described in the immediately preceding paragraph. 
   The projection from the flat nose of the bullet is preferably circular in plan, although this is not essential. The projection is preferably uniformly disposed about the longitudinal axis of the bullet to provide an even weight distribution and it could, if desired, be for example of square configuration in plan. 
   Where the projection is circular in plan, it may be of cylindrical configuration so as to have a flat outer end or it may be domed so as to have a curved outer end. 
   In a yet further aspect, the invention provides an apparatus for the manufacture of a bullet, the apparatus comprising a die, a first part of which defines a cylindrical cavity to receive the material to form the bullet, and two punch parts, one located at each end of the cavity whereby the material may be compressed in the cavity between the punch parts, the first part of the punch being shaped to define the rear portion of the bullet which is to be attached to a casing and the second part of the punch being shaped to have a hollow portion defining the curved portion and nose of the bullet, the curved portion ending in a flat face with a recess extending from the flat face to define a nose projection of the bullet. 
   In a conventional bullet press, the surface defining the cavity in which the bullet is formed between the two punch parts has a narrow sprue passageway leading into the cavity. The bullet is, therefore, formed with a sprue usually at right angles to its longitudinally extending body. 
   In the apparatus of the present invention, however, it is preferred that the sprue passageway be provided in the second part of the punch, extending from the recess which defines the nose projection in the general direction of the longitudinal axis of the bullet. If this sprue passageway extends completely through the second part of the punch, i.e. vents through the punch, we have found that improved bullet shape and uniformity with greater conformity to the final desired shape can be obtained. 
   In a still further aspect, the invention provides a method of manufacturing a bullet, the method comprising providing material to form the bullet, shaping the material to form the bullet characterised in that a front end of the bullet is formed with a centrally disposed projection extending from a flat nose in the direction of the longitudinal axis of the bullet. 
   Preferably, the method includes forming a reservoir of lubricant on the nose around the projection. 
   We have surprisingly found that the novel bullet shape of the invention can provide increased accuracy and consistency. Although not wishing to be limited to any particular theory, it is believed that one reason for the improvement over conventional bullet shapes is to do with the lubrication of the bullet. Bullets of the invention are coated as is conventional by coating with a liquid lubricant which is allowed to set on the outer surface of the bullet. The bullet may have conventional knurling on its cylindrical outer surface to provide reservoirs of the lubricant but we have found that an additional reservoir of lubricant can be provided during the coating process at the bullet nose around the base of the projection from the flat surface. This further reservoir can provide an extra degree of lubrication on firing of the ammunition so that the bullet surface is better protected as it travel along the barrel. 
   It is also believed that the bullet shape of the invention provides an improved relationship between the centre of gravity and the centre of pressure of the bullet. The centre of gravity normally lies within the cylindrical body portion of the bullet. The centre of pressure lies within the curved portion of the bullet and is the notional point where, when the bullet is fired, the lines of pressure normal to all points on the outer ogive surface meet inside the bullet. The centre of pressure in a bullet of the invention is moved further away from the centre of gravity, which is believed to improve balance and ballistic accuracy. 
   Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a conventional TENEX gullet, which is a high quality .22 rifle bullet; 
       FIG. 2  shows a first bullet of the invention; 
       FIG. 3  shows a second bullet of the invention; 
       FIG. 4  shows a third bullet of the invention; and 
       FIG. 5  shows a die for the manufacture of a bullet of the invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   In  FIG. 1  a conventional .22 bullet  10  has a rear cylindrical heel portion  12  with a concave cavity  14  in its rear face  16 . A step  18  leads from the front of heel portion  12  to a slightly larger diameter cylindrical central body portion  20 . At the front of the body portion  20  a step  22  leads to the tapered curved or ogive portion  24  at the front of which is the nose  26 . 
   It will be seen that the ogive portion  24  has a double curvature with a first region  28  extending from the body portion having a much greater radius than the front region  30  leading to the nose. 
   To form the desired 0.22 cartridge a metal casing  32  will be crimped to the heel portion  12  and then the bullet is coated with a suitable lubricant. The coating and crimping techniques are well known in the art. 
   In  FIG. 2  is shown a first bullet  100  of the invention. 
   This has a rear cylindrical heel portion  112  similar to the heel portion of the bullet  10  of FIG.  1 . Heel portion  112  has a concave cavity  114  in its rear face  116 . A step  118  leads to cylindrical central body portion  120  and a step  122  leads to a tapering curved front portion  124 . Portion  124  is of a single curvature and ends in a flat nose  126 . A central cylindrical projection  128  extends forwardly from flat nose  126 . 
   In  FIG. 3  is shown a second bullet  200  of the invention. 
   Again this has a rear cylindrical heel portion  212  with a concave cavity  214  in its rear face  216  and attached to a casing  232 . A step  218  leads to cylindrical central body portion  220  and a step  222  leads to a tapering curved front portion  224 . As with the bullet of  FIG. 2 , the front portion  224  is of a single curvature and ends in a flat nose  226 . A central cylindrical projection  228  extends forwardly from flat nose  226 . 
   In this embodiment the bullet  200  is shown after it has been coated with lubricant. As shown, a “reservoir”  230  of lubricant has collected and set around nose projection  228 . This reservoir provides additional lubrication as it can be forced to flow along the exterior of the bullet as it is fired through a gun barrel. 
   In  FIG. 4  is shown a third bullet  300  of the invention. 
   Again it has a rear heel portion  312  with a concave cavity  314  in its rear face  316 . A step  318  leads to cylindrical central body portion  320  and a further step  322  leads to a tapering curved front portion  324 . Portion  324  is again of a single curvature which ends in a flat nose  326 . Nose  326  has a centrally disposed cylindrical projection  328 . 
   It will be appreciated that the embodiments shown and described above are for exemplification of the invention only. The dimensions and radii indicated may be varied widely and may readily be adapted for bullets other than .22 calibre. 
   The projections from the flat nose need not be cylindrical and may, for example, as indicated above, be square in plan or domed. 
   The central body portion of the bullets will normally have conventional knurled regions applied to them to provide the usual reservoirs for lubricant. 
   In  FIG. 5  is illustrated an apparatus for the manufacture of a bullet of the invention. 
   The apparatus has a fixed die portion  400  defining a cylindrical moulding cavity  402  in which is shown a plug  404  of lead to be formed into a bullet of the invention. A first punch part  406  of cylindrical shape has an external diameter of size just to fit within cavity  402 . Part  406  has a domed end  408  extending from an annular land  410 , the land and domed end corresponding to the desired cavitied rear face of a bullet. A second punch part  412  is also of cylindrical shape and of external diameter just to fit into cavity  402  from the end opposite to that into which part  406  is to be fitted. Part  412  has a central cavity  414  of tapering curved shape corresponding to the desired curvature of the front portion of a bullet of the invention. At its innermost extent the cavity  414  has a flat portion.  416  to correspond to the flat nose of the bullet and a cylindrical recess  418  centrally disposed in flat portion  416  to form the projection from the flat nose. A sprue hole  420  leads from the recess  418  through the body of part  412  to vent to atmosphere. 
   When punch parts  406  and  412  are moved in the direction of arrows A and B respectively to enter cavity  402  of die  400 , the lead plug  404  is moulded to the desired novel bullet shape. The venting provided from cavity  414  and recess  418  ensures that the lead can completely fill those regions of punch part  412  to provide a satisfactorily formed shape.