Abstract:
A centerfire cartridge with improved ballistic characteristics for use in lever action firearms having tubular magazines is shown. A primer safety shield allows a sharper pointed bullet to be used without increased danger of inadvertent firing when a cartridge is placed in nose to base contact in a magazine.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates to firearms ammunition and more particularly to rifle and pistol centerfire cartridges for use in magazines where the cartridge primer may come in contact with the tip of adjacent cartridges. 
       BACKGROUND OF INVENTION 
       [0002]    The background of the firearms ammunition industry problems and challenges addressed in part by the present invention is set forth in great detail in the specification of U.S. Pat. No. 7,380,502 and is copied in part herein. 
         [0003]    Many popular types of rifles such as lever action rifles employ tubular magazines in which a single line of cartridges is stored in a cylindrical tube below the rifle barrel. The cartridges are arranged nose first with a compressed spring and piston forward of the nose of the forward most cartridge. The spring pressure transmits through the row of cartridges and forces the rear most cartridge into the action when the action is cycled. Centerfire cartridges have primers centered in the base of the cartridge and it is essential to ensure that the nose of one bullet does not act as a firing pin and strike the primer of the next cartridge. Traditionally this has required the use of blunt nosed bullets having diameters greater than the diameter of the centerfire primer to ensure any force transmitted to the primer is distributed over a large enough area to ensure that primer discharge will not occur. 
         [0004]    Unfortunately flat or blunt nose bullets are aerodynamically inefficient compared to pointed bullets used in other types of rifles. This means that they lose more velocity as a function of distance traveled than a sharp pointed bullet resulting in less energy downrange and increased errors requiring shooter adjustment. A ballistic coefficient (BC) of 0.200 depending on caliber and weight of the bullet is common for blunt nosed bullets while BC values of 0.250 to 0.350 are achieved with comparable sharp nosed bullets. Translated into hunting values a lever action rifle is considered effective to about 100-150 yards while spire point bullets of comparable weight and muzzle velocities are effective beyond 250 yards. 
       SUMMARY OF PRESENT INVENTION 
       [0005]    The present invention overcomes the flat nose bullet limitations of tubular type magazines such as the lever action rifle tubular magazines described in the referenced patent by providing a centerfire firearm cartridge with a safety shield about the primer such that the bullet fixed in such a cartridge may be more pointed than the traditional blunt nose bullets and substantially achieve the greater ballistic coefficients of more sharply pointed cartridges such as shown in the referenced US patent. By shielding the primer with a safety shield having a small central hole just large enough to admit a firing pin blunt nose bullets are no longer required to prevent unintended discharge of the primer and cartridge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a sectional side view of cartridges in a tubular magazine according to the present invention. 
           [0007]      FIG. 2  is a sectional view of three cartridges with A showing a prior art cartridge, B showing a modified case with large rifle primer and safety shield; and C showing a standard case with small primer and safety shield. according to the present invention; 
           [0008]      FIG. 3  is a sectional view of a small primer A, safety shield B, and assembly C; 
           [0009]      FIG. 4  is a view similar to  FIG. 3  with a large primer A, safety shield B, and assembly C; 
           [0010]      FIG. 5  is a sectional view of a cartridge case showing another embodiment of my invention; 
           [0011]      FIG. 6  is a view similar to  FIG. 5  showing a still further embodiment of my invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0012]    Referring now to  FIG. 2  cartridge A is a cross section of a conventional center fire cartridge body  10  standardized one hundred years or so ago. Millions and millions of this type of cartridge body have been made and many are still available for reloading with a new large primer  12 , powder and bullet of choice. Regardless of the caliber of the cartridge the diameter of the large primer has stayed at 0.212 inches and it has been made of cartridge brass that may be easily indented to compress the primer mixture against an anvil to fire the cartridge. 
         [0013]    Cartridge B of  FIG. 2  is a cross section of a first embodiment of my invention where a large primer  12  has been press fitted into a safety shield  14 . Shield  14  is cup shaped and has a center hole  16  in the base. Hole  16  must be large enough to admit the firing pin but small enough to exclude the more pointed tip of the bullet to be used in the cartridge. A range of 0.060-0.110 inches, depending on the diameter of the bullet tip, seems to be satisfactory. In a preferred embodiment a diameter of 0.100 inches has been found to be suitable. A typical shield  14  might have an outside diameter of 0.266 inches. Shield  14  is preferably made of nickel plated steel with a thickness sufficient to prevent firing of the primer by recoil or other shock. The assembled shield  14  and primer  12  are press fitted into an appropriately enlarged cavity in the base of the cartridge  10 ′. While this would require modification of existing cartridge bodies and changing of the primer cavity dimensions in new manufacture the existing large primers could still be used. 
         [0014]    Cartridge C of  FIG. 2  shows a variation of my invention in which the large primer cavity diameter of 0.212 inches is maintained in the cartridge body  10 ″ and a smaller safety shield  18  is used to protect a “small” primer  20  which usually has an outside diameter of 0.175 inches. Again shield  18  has a center hole  22  with a diameter of 0.100 inches an inside diameter of 0.175 inches and an outside diameter of 0.212 inches. These dimensions allow the primer  20  to be press fitted into the shield  18  and the assembly press fitted into the large primer cavity in the standard cartridge body. Shield  18  is preferably made of nickel plated steel with sufficient strength so the thinner wall will still protect the primer from firing. It may be seen that in cartridge C the height of small primer  20  may be shorter than standard since safety shield  18  is sized to just fit in the large primer cavity in standard cartridges. 
         [0015]    As shown in  FIG. 1  the foregoing safety shields  14  and  18  prevent pointed bullet nose  24  from contacting the primer of the bullet in front of it. Obviously the bullets will not always be in perfect alignment as shown in  FIG. 1  but when skewed there is even less possibility of contact with the primer. 
         [0016]    Referring now to  FIG. 3  a small primer cup  26  is shown with safety shield  28  sized to receive cup  26  in a press fit and the complete assembly staying within the outside diameter of 0.212 inches to allow press fitting in the standard cartridge body primer cavity. With this configuration of my invention the millions of existing cartridge shells can be reloaded using standard readily available parts and tools. Also new cartridges made with this safety shield may be used in lever action rifles with tubular magazines without sacrificing any appreciable accuracy or range with safety equal to or better than blunt nose bullets. 
         [0017]    Referring now to  FIG. 4  a primer safety shield for the large primer with its 0.212 inch outside diameter and 0.118 inch depth. Here typically the safety shield would have an outside diameter of 0.266 inches and an overall depth of 0.145 inches. While this would require resizing the primer cavity in the standard cartridge, for some applications it may be preferable to the configuration of  FIG. 3 . 
         [0018]      FIG. 5  shows another embodiment of the invention in which the safety shield takes the form of a nickel plated steel flat washer  30  with a center hole of 0.100 inches press fitted into the base of the cartridge below the primer  32 . This configuration gives the same protection and performance advantages as the foregoing alternatives although requiring some additional modification to the standard cartridge cases. 
         [0019]      FIG. 6  shows a still further embodiment in which a nickel plated washer  34  having a central hole of 0.100 inches diameter and an outer diameter matching the primer  36  used in the primer cavity of the cartridge. It is affixed to the primer  36  before press fitting the assembly into the cartridge body. Safety shield washer  34  may be epoxyed, welded or otherwise affixed to the primer bottom. 
         [0020]    While there are given above certain specific examples of this invention and it application in practical use, it should be understood that they are not intended to be exhaustive or to be limiting of the invention. On the contrary these illustrations and explanations herein are given in order to acquaint others skilled in the art with this invention and the principles thereof and a suitable manner of its application in practical use.