Patent Publication Number: US-8991084-B2

Title: Apparatus and methods for tracking ammunition supply in a magazine

Description:
PRIORITY CLAIM 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/776,510 filed Mar. 11, 2013, and entitled METHODS FOR TRACKING AMMUNITION SUPPLY IN A MAGAZINE, which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to magazines for a firearm and, more particularly, to apparatus and methods for determining a number of rounds in a magazine. 
     BACKGROUND OF THE INVENTION 
     It can be extremely dangerous if a firearm runs out of ammunition in a critical situation for a soldier, law enforcement officer, hunter, or citizen required to use a firearm in self-defense. Typically, the only indication that a magazine is empty is the clicking of a firing pin in an empty chamber or the slider or bolt of the firearm locking in an open position. Of course, a user may simply count shots, but this is a difficult task to perform in a dangerous situation. 
     Most magazines do include some sort of indicator of rounds left. For example, a typical box magazine inserted within a grip of a pistol may include holes on the side of the magazine such that rounds within the magazine are visible when the magazine is removed. Numbers may even be printed or stamped next to each hole to indicate the number of rounds contained in the magazine up to that hole. However, these indicators are useful when loading but are not visible when the magazine is positioned within the firearm. 
     Accordingly, it would be an improvement in the art to provide a magazine enabling a user to determine a number of rounds therein while the magazine is inserted within a firearm. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a magazine includes a storage tube defining a proximal end and a distal end, the proximate end defining an opening for loading the magazine with rounds. A biasing member is positioned within the storage tube and has a first end and a second end, the first end being positioned closer to the proximal end than the second end. A display member is coupled to the biasing member and is viewable through the storage tube. The display member configured to display a state of the biasing member. 
     In some embodiments, a strip couples the biasing member to the display member. The display member may be a transparent member affixed to the storage tube and the strip may have position indicators defined thereon that are viewable through the transparent member from outside the storage tube. The strip may include an elastic material and have a rolled-up shape absent forces exerted on the strip. 
     In another aspect of the invention, a spool is rotatably coupled to the magazine having the biasing member positioned between the spool and the proximal end, at least a portion of the strip being wound around the spool. A return spring may have one end affixed to the spool and another other end fixed relative to the storage tube, the return spring being effective to urge the spool to wind the strip further around the spool. In some embodiments, a cap covers the distal end of the storage tube and the spool is rotatably mounted to the cap. 
     In another aspect of the invention, the display member is an arcuate window and protrudes from the distal end of the storage tube, the spool may be partially encircled by the arcuate window such that a portion of the strip wound onto the spool is visible through the arcuate window. In some embodiments, the strip has a plurality of numbers printed along the length thereof such that a number of the plurality of numbers that is visible through the arcuate window indicates a number of items positioned within the storage tube. 
     In another aspect of the invention, a switch is positioned between the cap and the biasing member such that urging the biasing member toward the distal end urges the switch against the cap and changes a state of the switch effective to cause the switch to couple a power source to a light emitting device. The light emitting device is positioned to illuminate a portion of the strip that is wound around the spool and visible through the display member. 
     A method of use for the magazine is also disclosed and claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  is an isometric view of a firearm incorporating a magazine in accordance with an embodiment of the present invention; 
         FIG. 2  is an isometric view of a magazine in accordance with an embodiment of the present invention; 
         FIG. 3  is a partial cutaway view of a magazine in accordance with an embodiment of the present invention; 
         FIG. 4  is an exploded view of a magazine in accordance with an embodiment of the present invention; 
         FIG. 5  is a partial cross-sectional view of a magazine in accordance with an embodiment of the present invention; 
         FIG. 6  is a partial cross-sectional view of an alternative embodiment of a magazine in accordance with an embodiment of the present invention; 
         FIG. 7  is a partial cross-sectional view of another embodiment of a magazine incorporating a switch in accordance with an embodiment of the present invention; 
         FIG. 8  is a partial cross-sectional view of the embodiment of  FIG. 7  having the switch in a closed state in accordance with an embodiment of the present invention; 
         FIG. 9  is a side cross-sectional view of yet another embodiment of a magazine in accordance with an embodiment of the present invention; 
         FIG. 10  is an isometric view of the magazine of  FIG. 9 ; and 
         FIGS. 11 and 12  illustrate alternative embodiments of windows for a magazine in accordance with any of the foregoing embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a magazine  10  may insert within a firearm  12 . The illustrated firearm  12  is a pistol including a grip  14  for gripping by a user and an action  16  secured to the grip  14 . The action  16  may include the elements of a firearm for firing a round including such elements as a firing pin, chamber, trigger mechanism, slide, barrel, etc. that are needed to implement an automatic, semi-automatic, single-action, double-action, single-shot or other type of firing mechanism for a firearm. The action  16  may be any action known in the art that may be used with a magazine, i.e. includes a feeding mechanism to feed a round from the magazine  10  into a chamber for firing in an automatic, semi-automatic, or single-shot fashion. The illustrated magazine  10  is a “box” magazine however the principles of the invention disclosed herein may also be applied to tube, drum, rotary, and other magazines. 
     The magazine  10  may include a storage tube  20  having a distal end covered by a cap  18 . The cap  18  may be translucent or have a translucent window  22 . The window  22  may simply be a hole passing through a wall of the cap  18  or be embodied as a hole passing through the cap  18  and having a piece of translucent material inserted therein. 
     A strip  24  may be disposed within the magazine  10  such that a portion thereof is visible through the window  22 . The strip  24  may have printed, stamped, embossed, engraved, or otherwise defined thereon one or more visual indicators  26 . The visual indicator  26  that is visible through the window  22  or at a defined position within the window  22  may indicate a number of rounds in the magazine  10  as described in greater detail herein below. The visual indicators may be numerals, symbols (a number of tick marks), or some other symbol indicating a number of rounds. The window  22  may include translucent material inserted therein that is contoured to magnify the visual indicators to enhance readability thereof, e.g. a lens. 
     Referring to  FIG. 2 , a proximal end of the storage tube  20  opposite the cap  18  may define an opening  28  through which rounds may be inserted in order to fill the magazine  10 . As is apparent in  FIG. 2 , a major portion, e.g. 80% or more, of the length of the storage tube  20  has a constant cross-sectional shape along an axis  30 . In the illustrated embodiment, this cross-sectional shape is a chamfered rectangle. In other embodiments, the cross sectional shape may be round or some other shape. 
     Rounds  32  may be inserted into the magazine  10  by feeding a round into the opening  28  under a lip  34  extending partially over the opening  28  as known in the art. The lip  34  may retain rounds within the storage tube  20 . Rounds  32  may be inserted into the opening  28  having the axis of symmetry thereof oriented generally perpendicular (e.g. within +/−15 degrees of perpendicular) to the axis  30  as known in the art. Rounds  32  stored in the storage tube  20  may have the axis of symmetry thereof generally perpendicular to the axis  30 . Where the magazine  10  is a tubular magazine, the axis along which the storage tube  20  has constant cross section is generally parallel (e.g. within +/−5 degrees of parallel) to the axes of symmetry of rounds  32  inserted therein. A lip  34  may retain rounds in the magazine as known in the art. In some embodiments, holes  36  perforating the storage tube and distributed along the axis  30  may enable a user to see rounds within the storage tube  20 . 
     Referring to  FIG. 3 , a follower  38  may be slidably positioned within the storage tube  20 . The follower  38  may define an upper surface  40  for engaging the rounds  32  and one or more walls  42  extending downwardly from the upper surface  40 , e.g. away from the rounds  32 . The walls  42  may resist twisting of the follower  38  within the storage tube  20 . A follower spring  44  is positioned between the follower  38  and the cap  18 . The spring  44  urges the follower  38  toward the opening  28  thereby urging rounds  32  out of the magazine  10  and/or against the lip  34 . 
     Referring to  FIG. 4 , a clip  46  may be interposed between the follower  38  and the follower spring  44 . The clip  46  may define a flange  48  having an aperture  50  defined therein. The aperture  50  may receive a fastener securing the strip  24  to the flange  48 . The clip  46  may define another flange  52  opposite the flange  48  such that a portion of the follower spring  44  is positioned between the flanges  48 ,  52 . In the illustrated embodiment, the flange  52  is folded inwardly or hooked toward the flange  48 , such that a portion of the follower spring  44  is partially encircled by the flange  52 . The strip  24  may also secure directly to the follower rather than by means of a clip  46  and the clip  46  may have any configuration for retaining the strip  24  with respect to the follower  38 . 
     The cap  18  may be secured to the storage tube  20  by any means known in the art. For example, the cap  18  may be secured to the storage tube  20  by means of fasteners, adhesive, welds, or any other fastening means. In the illustrated embodiment, ridges  54  defined along a distal end of the storage tube  20  are received within slots  56  defined by the cap  18  such that the cap  18  may be slid over the end of the storage tube  20 . The slots  56  may be sized such that the slots  56  grip the ridges  54  and no further fastening means are needed. Adhesive may further be used to secure the ridges  54  within the slots  56 . A fastener may also engage the storage tube  20  and cap  18  in order to prevent disengagement of the ridges  54  from the slots  56 . 
     The cap  18  may define an opening  58  for receiving a portion of a housing  60 . Alternatively, the housing  60  may be an integral or monolithic part of the cap  18 . The housing  60  may receive a portion of the strip  24  as it is wound, responsive to movement of the follower  38  toward the cap  18 . In the illustrated embodiment, the housing  60  includes an upper housing portion  62  and a lower housing portion  64  that between them define a drum-shaped cavity with the boundary between the upper housing portion  62  and lower housing portion  64  being parallel to, and possibly intersected by, an axis of symmetry of the drum-shaped cavity. The axis of symmetry of the drum may be perpendicular to the axis  30  of the storage tube  20 . 
     The window  22  may be defined on, or secured to, the lower housing portion  64  and the lower housing portion  64  may protrude through the opening  58  such that at least a portion of the window  22  is exposed through the opening  58 . As is apparent, the window  22  may have an arcuate shape, such as a portion of a cylinder. The window  22  may define a portion of a cylindrical wall of the drum-shaped cavity. 
     The drum-shaped cavity may include therein an axle  68  parallel to, and possibly centered on, an axis of symmetry of the drum-shaped cavity defined by the upper and lower housing portions  62 ,  64 . The axle  68  may insert within a spool  66  such that the spool is rotatable about the axle  68 . In the illustrated embodiment, the axle  68  is secured to a planar locator plate  70  that maintains the axle  68  in a desired position within the drum-shaped cavity. In the illustrated embodiment, the locator plate  70  includes a rounded surface  72  sized to conform to an inner surface of the drum shaped cavity defined by the lower housing portion  64 . The locator plate  70  may include a flat surface  74 . The flat surface may abut a portion of the upper housing portion  62  and prevent rotation of the locator plate  70 . Alternatively, the rounded surface  72  may engage a cylindrical surface within the upper housing portion  62  and the flat surface  74  abuts the lower housing portion  64 . 
     In some embodiments, a spring  76  is coupled between the spool  66  and the axle  68  such that the spring is deformed as the spool  66  is rotated due to tension on the strip  24 . The spring rotates the spool  66  when tension on the strip  24  is reduced. In the illustrated embodiment, the spring  76  is a constant-force spring wound around the axle  68  and having one end fixed relative to the axle and another end coupled to the spool  66 . As known in the art, a constant force spring is a flat strip of elastic material, such as metal or resilient polymer, rolled into a coil. 
     In some embodiments, a perimeter of the spool  66  that is not covered by the strip  24 , e.g. a rim on either side of the strip  24 , may be marked with numerals or other symbols such that the position of the spool as viewable through the window  22  indicates a number of rounds in the magazine, rather than visual indicators  26  ( FIG. 1 ) defined on the strip  24 . In such embodiments, the strip  24  may be made arbitrarily thin since it does not need to be wide enough to have readable numerals or symbols printed thereon. The strip  24  may be a thin cable, wire, polymer filament, or the like. 
       FIG. 5  illustrates the strip  24  wound around the outside of the spool  66  whereas the spring  76  is positioned within the spool  66 . The axle  68  may define a slot  78  extending partially or completely through the axle  68  and an end of the spring  76  may be positioned within the slot  78  such that the end of the spring  76  is restrained from rotating. The axle  68  may be affixed to the lower housing portion  64  or prevented from rotating due to the locator plate  70 . 
     The other end of the spring  76  may be coupled to the spool  66 . For example, as shown in  FIG. 5 , the spring extends out of the spool  66  through opening  80  and then inserts back into the spool through opening  82  to affix an end portion  84  of the spring  76  to the spool  66 . The friction between the spring  76  and the spool  66  may be sufficient to prevent removal of the end portion  84  from the openings  80 ,  82  due to forces exerted during expected operating conditions. In some embodiments, the end portion  84  of the spring  76  inserted through the opening  82  may be hooked or otherwise permanently deformed to further affix the spring  76  to the spool  66 . 
     The upper housing portion  62  may define a slit  86  or other opening through which the strip  24  may pass. As shown, the slit  86  may be positioned on one side of the upper housing portion  62  and sized such that the strip  24  may pass through the slit  86  and around the spool  66  without contacting the sides of the slit  86  or being deformed by the slit  86 . 
     As noted above, the upper housing portion  62  defines a cylindrical surface  88  and the lower housing portion  64  defines a cylindrical surface  90  that together form a drum-shaped cavity having a diameter large enough to received the spool  66  as well as allow for rotation of the spool when the strip  24  is wrapped around the spool a number of times, e.g. 5 to 10 times, without interference. 
     The upper housing portion  62  may define a flange  92  extending partially or completely around the drum-shaped cavity and the lower housing portion  64  may define a flange  94  extending partially or completely around the drum-shaped cavity. The flange  92  of the upper housing portion  62  may include a tab  98  and the flange  94  of the lower housing portion  94  may include a groove sized and positioned to receive the tab  98  in order to align the upper and lower housing portions  62 ,  64  and at least partially restrain relative movement therebetween. In the illustrated embodiment, the cap  18  defines a seat  100  or recessed portion  100  for receiving the flange  94 . In some embodiments, the pressure of the follower spring on the upper housing portion  62 , such has the flange  92 , maintains the lower housing portion within the seat  100  and opening  58  in the cap  18  absent any other fasteners. This arrangement reduces the likelihood of damage to the lower housing portion  62 , upper housing portion  64 , and components mounted thereon inasmuch as an impact on the lower housing portion  64  will simply drive the lower housing portion  62  into the storage tube  20  against the biasing force of the follower spring  44 . 
     Referring to  FIG. 6 , in some embodiments the spool  66  and spring  76  may be omitted. Instead, the strip  24  may itself be embodied as a constant force spring including a hooked or angled end portion  102  engaging the slot  78  of the axle  68 . Accordingly, a restoration force generated by the strip  24  may urge the strip  24  to wind around the axle  68  responsive to compression and decompression of the follower spring  44 . In the embodiments above, the strip  24  may also be embodied as a constant force spring, though the spring  76  assists in winding of the strip  24  around the spool  66 . In some embodiments, the strip  24  may include two parts: a measuring portion that includes markings (text, symbols, etc.) indicating a number of rounds in the magazine and a spring portion embodied as a constant force spring. The measuring portion may secure at one end to the follower  44 , such as by means of clip  46  ( FIG. 4 ) and at an opposite end to the spring portion, the spring portion being wound around the axle  68  and engaging the slot  78  or otherwise affixed to the axle  68 . 
     In some embodiments, the coiling of the portion of the strip  24  within the chamber defined by the upper and lower housing portions  62 ,  64  is sufficient to resist removal of the coiled portion from the drum-shaped chamber. In such embodiments, the axle  68  may be omitted and the strip  24  may coil and uncoil responsive to compression and expansion of the follower spring  44  without being restrained by the axle  68 . In such embodiments, the opening  86  may be small enough to prevent the strip  24  from completely exiting the chamber responsive to expansion of the follower spring  44 . 
     Referring to  FIG. 7 , in some embodiments, the upper and lower housing portions  62 ,  64  define a chamber that is other than drum-shaped. For example, the upper housing portion  62  may define a planar surface  104  and the lower housing portion  64  defines a bell-shaped surface  106  that together define a chamber for winding of the strip  24  around the axle  68  or around a spool  66  mounted to the axle  68 . 
     In some embodiments, a light source  108 , such as an LED may illuminate the chamber defined by the upper and lower housing portions  62 ,  64  to facilitate viewing of the visual indicators  26  on the strip  24 . In the illustrated embodiment, the light source  108  protrudes into the chamber through an opening  110  defined by the upper housing portion  62  or emits light through the opening  110 . 
     In some embodiments, the light source  108  may be activated by a switch  112  that is depressed responsive to compression of the follower spring  44 . That is to say, the follower spring  44  may press against the switch  112 . When the pressure exerted by the follower spring  44  on the switch  112  exceeds a threshold, the switch  112  will change state (e.g. close or open a circuit). When the pressure exerted by the follower spring  44  on the switch  112  is below the threshold, the switch may again change state (e.g. open or close a circuit). The switch  112  may include a biasing member  114  that determines this threshold, i.e. provides a resistance force that must be overcome to depress the switch and change its state. 
     In the illustrated embodiment, printed circuit board  116  (“PCB  116 ”) has the switch  112  mounted thereto such that the PCB  116  is positioned between the switch  112  and the follower spring  44 . Force exerted by the follower spring  44  on the PCB  116  urges the switch  112  against a portion of one or more of the upper housing portion  62 , lower housing portion  64 , and the cap  18  in order to change the state of the switch  112 . In the illustrated embodiment, the upper housing portion  62  defines a seat  118  in which the PCB  116  is positioned. The light source  108  and switch  118  may both protrude through the opening  110  and the switch  112  may engage a portion of the cap  18 . 
     The PCB  116  may have circuits and electronic components mounted thereon to drive the light source  108  responsive to changing of the state of the switch  112 . A battery  120  may be electrically coupled to the PCB  116  for powering the PCB  116  and light source  108 . In some embodiments, the PCB  116  includes electronic components that detect closing of the switch  112  and, in response, activate the light source  108 . The PCB  116  may include a timer and include electronic components that deactivate the light source  108  upon expiration of a time period following closing of the switch  112 . The electronic components of the PCB  116  may further deactivate the light source  108  upon detecting opening of the switch  112 . 
     In use, a user may turn on the light source  108  by pushing up on the lower housing portion  64  thereby pushing the PCB  116  and switch  112  upward and allowing the switch  112  to return to an open state. Upon releasing the lower housing portion  64 , the follower spring  44  again urges the switch  112  into a closed state, prompting the PCB  116  to turn on the light source  108 , which may include starting a timer or counter such that the PCB  116  turns off the light source  108  after expiration of a time period as determined by the timer or counter. In some embodiments, the circuits of the PCB  116  may detect opening and closing the switch  112  and in response turn the light source  108  off if the light source  108  was on at the time of detecting opening and/or closing of the switch  112 . 
     In some embodiments, compression of the switch  112  due to biasing force of the follower spring  44  may cause the switch  112  to go to an open state and decompression of the switch  112  due to an upward force on the lower housing portion  64  causes the switch  112  to go to a closed state. In such embodiments, the PCB  116  may include circuits that detect the momentary changing of the switch  112  to a closed state and, in response, cause the light source  108  to turn on if it was previously off, turn off if it was previously on, or take some other action with respect to the supply of power to the light source  108 . 
     In some embodiments, the light source  108  may be embodied as an ultraviolet (UV) light source and the ink used to print the visual indicators  26 , or a treatment on the surface of the strip  24  around the visual indicators  26 , may glow responsive to this light in order to enhance visibility of the visual indicators  26 . The spool  66  may also include or be treated or coated with a material that glows responsive to UV light to further enhance visibility of the visual indicators  26 . The visual indicators  26  may also have reflective treatments to enhance their visibility responsive to light from the light source  108 , UV, visible, or otherwise. 
     Referring to  FIGS. 9 and 10 , in some embodiments, the strip  24  may extend between the follower spring  44  and a wall of the storage tube  20 . In this manner, buckling of the of the strip  24  is prevented. Accordingly, the strip  24  may not be embodied as a constant force spring since the movement of the follower  38  can push the strip  24 . The strip  24  may have a concave cross section such that it has further rigidity to resist buckling during pushing of the strip  24 . The cap  18  may have a window  22  and guide  122  positioned opposite the window  22  such that the strip  24  is pushed between the window  22  and guide  122  in order to display a number, or other visual indicator, on the strip  24  that is positioned in front of the window  22 . 
     In the illustrated embodiment, the cap  18  includes a plate  124  that engages the storage tube  20  and defines a slot  126  through which the strip  24  passes out of the storage tube  20  and past the window  22 . The slot  126  may be an opening defined in the plate  124  or a gap between the plate  124  and an edge of the storage tube  20 . The window  22  may be positioned relative to the slot, such as abutting the lower edge of the storage tube  20  or otherwise positioned over the strip  24  as it protrudes from the storage tube  20  such that visual indicators on the strip  24  are visible through the window  22 . 
     The cap  18  may further include a cover  128  secured to the plate  124  and contains the portion of the strip  24  extending outwardly from the storage tube  20 . In the illustrated embodiment, the cover  128  is a curled or bent piece of metal or other material having an upper portion  130  secured to the plate  124  and curled such that an edge of the  132  of the cover  128  is positioned abutting or overlapping the window  22 . The edge  132  of the cover  128  may abut the plate  124  or the storage tube  20  and the window  22  may be defined by an aperture in the cover  128  that may be occupied by a transparent material. As is apparent in  FIG. 10 , the sides of the cover  128  may be open. However, sides may be secured to the cover  128  either monolithically or by securement by a fastening means. 
     Referring to  FIG. 11 , in some embodiments, as noted above, a spool  66  may have visual indicators  26  formed thereon. In some embodiments, the visual indicators  26  may be formed on an axial surface of the spool, e.g. the axis of the spool  66  is normal to the surface on which the visual indicators  26  are formed. Accordingly, a window  134  may be defined in the lower housing portion  64  parallel to the axial surface such that a least one visual indicator  26  printed on the axial surface is visible through the window  134 . As shown in  FIG. 12 , the lower housing portion  64  may include both a window  22  as defined hereinabove and a side window  134 . 
     While the preferred embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, although the illustrated magazine is a box type magazine, the strip  24  may be coupled to a follower of tubular type magazine and the spool  66  and/or axle  68  may be mounted to the tubular magazine such that the strip  24  may be taken up or unwound responsive to movement of the follower. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.