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You are an expert at summarizing long articles. Proceed to summarize the following text: 
RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/US2010/56201, which designated the United States and was filed on Nov. 10, 2010, published in English, which claims the benefit of U.S. Provisional Application No. 61/260,484, filed on Nov. 12, 2009. The entire teachings of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     There has been an ongoing search for the convenient storage of handguns including but not limited to pistols and revolvers. Often, handguns are stored on their sides either in drawers or on shelves. Handguns take up significant space when stored in this manner. This is particularly troublesome for individuals who collect handguns and have limited storage space. This dilemma is compounded by the laws of some states and jurisdictions that require guns to be stored in locked enclosures such as gun safes, to prevent unauthorized use of guns by third parties. Most gun safes manufactured today do not provide a convenient means for storing multiple handguns within the safe in a space-saving manner. Space is a premium in a safe and the storage of multiple handguns quickly takes up available space in the safe. A convenient means for storing multiple handguns in any location and particularly in an enclosure having limited space such as a gun safe is desirable. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention provides a free-standing handgun stack for storing multiple handguns in a single column vertical stacking arrangement. 
     In another embodiment the invention provides a handgun stack for storing multiple handguns in a single column vertical stacking arrangement wherein the handgun stack is retrofitable for permanent or removable attachment to the inside of a gun safe. In one aspect of this embodiment, the gun stack is configured to a height and width that takes up about the same amount of space as a long gun if such long gun were disposed or secured in a vertical position in the same space within the gun safe. 
     In accordance with the invention, the handgun stack of the invention is suitable for holding at least two handguns in a single column vertical stacking arrangement wherein each handgun comprises a grip and a barrel, wherein the handgun stack comprises: 
     a pair of opposing vertical side walls; and 
     at least two slots vertically arranged one on top of the other disposed between the pair of side walls and supported by the side walls, wherein each slot has a top surface and a bottom surface extending at a downward angle from a front access opening through the slot to a rear exit opening, wherein each slot is separately accessible through the front access opening, wherein each slot is separately adapted to receive a handgun through the front access portion; each slot providing the bottom surface upon which the handgun rests in an upright position, wherein upon placing the handgun in the slot through the front access opening, the barrel of the handgun is preferably angled downward and away from the front access opening and extends toward or through the rear exit opening and the grip of the handgun is angled upward and extends out of the front access portion of each slot. 
     In one embodiment, the individual slots of the handgun storage stack are not angled down, but are instead configured at 90° to the side walls and parallel to the floor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained and described in more detail below using embodiments shown in the drawings. The described and drawn features in other embodiments of the invention can be used individually or in preferred combinations. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed on illustrating principals of the invention in a clear manner. 
         FIG. 1  is a perspective view of the invention. 
         FIG. 2  is a cutaway side view of the invention. 
         FIG. 3  is a perspective view of a gun safe wherein the handgun stack of the invention is installed inside of the gun safe. 
         FIG. 4A  is a top down view of the configuration of a first gun safe interior surface element. 
         FIG. 4B  is a top down view of the hand gun stack showing a first interlocking element on the exterior of the handgun stack that is configured to mate with a first gun safe interior surface element of  FIG. 4A . 
         FIG. 4C  is a top down view of the configuration of a second gun safe interior surface element. 
         FIG. 4D  is a top down view of the hand gun stack showing the second interlocking element on the exterior of the handgun stack that is configured to mate with the second gun safe interior surface element of  FIG. 4C . 
         FIG. 5  is a perspective view of one embodiment showing a configuration for securing the handgun stack to the interior of a gun safe. 
         FIG. 6  is a top down view showing one configuration of  FIG. 5  for securing the handgun stack to the interior surface of a gun safe. 
         FIG. 7  is a top down view showing an alternative configuration of  FIG. 5  for securing the handgun stack to the interior surface of a gun safe. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , the handgun stack of the invention is shown generally at  10  comprising a pair of opposing side walls  12 ; optionally, a top  14  and optionally a base  16 . At least two handgun storage and receiving slots  18  are vertically arranged one on top of the other and disposed between the pair of side walls  12  and having interior sides  36  defined by the side walls  12 , wherein each slot has a top surface  20  and a bottom surface  22 . In one embodiment, the handgun stack  10  of the invention is free standing and is supported on and by the base  16 . 
     Turning now to  FIG. 2 , each slot  18  extends at a downward angle from a front access opening  24  through the slot to a rear exit opening  26 , wherein each slot  18  is separately accessible through the front access opening  24 , wherein each slot is separately adapted to receive a handgun  28  through the front access opening  24 ; each slot providing the bottom surface  30  upon which the handgun  28  rests in a generally upright position, wherein upon placing the handgun  28  in the slot  18  through the front access opening  24 , the barrel  32  of the handgun  28  is angled downward and away from the front access opening  24  and extends toward or through the rear exit opening  26  and the grip  34  of the handgun  28  is angled upward and extends out of the front access portion  24  of each slot  18 . 
     In one embodiment, the total width of handgun stack  10  is only slightly larger than the width of most standard long guns resting in an upright position thereby facilitating space saving. The total length of the handgun stack  10  can be of any convenient size or height. In a preferred embodiment, the width and length of the handgun stack of the invention are about the same as the width and length of the space in a gun safe designated for the securing and holding of one long gun such as a rifle, scoped rifle, shotgun or scoped shotgun as will be discussed in more detail below with respect to  FIG. 3 , thereby facilitating retrofitting, inserting, or otherwise installing of the handgun stack into a gun safe wherein the handgun stack takes up about the same amount of space as a long gun in the safe. 
     The slots  18  of the handgun stack of the invention can be adapted to fit a handgun of almost any size, including handguns with long barrels or custom stocks or scopes. As shown in  FIG. 2 , the bottom surface  22  of the slot may include a step up  38  against which the trigger guard  46  of the handgun  28  rests for further security in the slot  18 . It is another benefit that the gun stack of the invention presents a gun to a user in a safe manner oriented and positioned exactly where the user can easily grip it, but with the barrel facing away from the user for added safety. 
     Referring again to  FIG. 1 , the top surface  20 , the bottom surface  22 , and the sides  36  of slots  18  may be lined with a non-abrasive material including but not limited to felt, cotton, or other soft synthetic material such as polyester or rayon to prevent scratching of the gun surface. In one embodiment, the top surface  20 , the bottom surface  22 , and the sides  36  slots  18  may be partially or fully padded with foam or the like, such as to render the gun generally immobile against the padding once the gun is placed in the slot. 
     The handgun stack of the invention may be made of any suitable material that is strong enough to support the weight of a plurality of handguns that may be stored in the handgun stack. Such materials include but are not limited to wood, plastics, metals or other composite lightweight materials. 
     Referring now to  FIG. 3 , the handgun stack  10  of the invention may be conveniently retrofitted to a gun safe  40 . In one embodiment, the handgun stack  10  of the invention is configured to have a width and length that occupies about the same space as a long gun  42  when stored in the safe  40 . The actual length may vary depending on the size of the gun safe, but the width can be determined based on the average width of the most popular types of long guns. In one embodiment, the total width of the handgun stack of the invention may range from about 1.5″ to about 4″. In one embodiment the width of the interior of a slot may range from about 1.0″ to about 3.9″. In one embodiment, the width of the gun stack is 2.25 inches wide. In one embodiment the depth of the gun stack is 6 inches. In one embodiment the height of the gun stack is 45 inches. The handgun stack of the invention may be removably or permanently retrofitted to the interior of a safe. For permanent attachment, many safes are manufactured with brackets and bracket extenders offset from one of the interior walls, usually the back wall of the safe for receiving or securing long guns. The handgun stack of the invention may be suitably designed to include cut outs or holes through which a bolt can be inserted into the preexisting bracket of the gun safe thereby securing the handgun stack to an interior surface of the gun safe. This arrangement is particularly convenient as the offset of the bracket from the back wall of the gun safe also offsets the rear opening of the gun stack from the back wall thereby leaving room for any gun barrels protruding through the rear opening  26  of the gun stack as shown in  FIG. 2 . 
     In another embodiment, the handgun stack of the invention may be removably secured within a gun safe using a hook and loop arrangement such as VELCRO®. In this embodiment, an interior rear surface of a gun safe for example is capable of receiving and mating with a corresponding hook and loop surface that is attached to the exterior rear portion of the gun stack of the invention. 
     In an another embodiment the handgun stack may be removably secured within the gun safe using a system of straps, such as bungee cords, which can be simply wrapped around the gun stack of the invention and hooked on one or more interior surfaces or brackets located in the interior of the gun safe. In yet another embodiment, an exterior surface (e.g. the rear exterior surface) of the gun stack of the present invention may include one or more elements that are configured and sized to mate with one or more corresponding elements in the gun safe adapted to hold a long gun.  FIG. 4A  shows a configuration of a first gun safe interior surface element  48 .  FIG. 4B  shows a first interlocking element  50  on the exterior surface of the handgun stack  10  that is configured to mate with the first gun safe interior surface element  48  of  FIG. 4A . Likewise,  FIG. 4C  also shows a configuration of a second gun safe interior surface element  52 . A second interlocking element  54  on the exterior surface of the handgun stack  10  is shown in  FIG. 4D  and is configured to mate with the second gun safe interior surface element  52  of  FIG. 4C . 
       FIG. 5  shows another embodiment for removably securing the handgun stack within a gun safe. In this embodiment, the rear exterior surface  105  of the handgun stack  100  is fitted with opposing parallel shafts  110  that extend longitudinally along the rear surface  105  of the handgun stack  100 . The shafts  110  are capable of receiving the head  120  of the T-shaped key  115  which in turn can be slid up and down the shafts  110 . The stem  125  of the T-shaped key  115  is capable of fitting into an opening  130  (e.g. such as a slot) of the plate  135 . The plate  135  is in turn adapted to be secured onto an interior surface of a gun safe such as is shown in  FIG. 6 . 
     An alternative embodiment of  FIG. 5  is shown in  FIG. 7  where instead of using the plate  130 , the plate  130  is substituted with a ring  140  shown in  FIG. 7  wherein the stem  125  of the T-shaped key  115  shown in  FIG. 5  is capable of being received by the ring  140  of  FIG. 7 . 
     The embodiments of  FIGS. 5 ,  6  and  7  show that the plate  135  of  FIG. 5  or the ring  140  of  FIG. 7  is secured to the interior surface  145  of a gun safe such as an interior element  155  of the gun safe which may be curved and configured to hold a long gun all as shown in  FIGS. 6 and 7 . In operation, the head  120  of the T-shaped key  115  as shown in  FIG. 5  is inserted into the shafts  110  on the rear of the handgun stack  100  as shown in  FIG. 5 . In turn the stem  125  of the T-shaped key  115  is then slid along the shafts  110  and inserted into the opening  130  of the plate  135  of  FIGS. 5 and 6 . Alternatively, the stem  125  of the T-shaped key as shown in  FIG. 5  is inserted into the ring  140  of  FIG. 7 . For each embodiment said respective ring  140  of  FIG. 7  or plate  135  of  FIG. 6  have been previously secured by the user to the interior surface element  155  of a gun safe  145  as shown in  FIGS. 6 and 7 . 
     It is understood that the gun stack of the invention may be fitted to, installed in or otherwise optionally secured in any enclosed space such as a closet, or armoire or display case. 
     The gun stack may also be conveniently placed in a locker or even a firearms safe room such as that a police department may have for convenient access to firearms. The gun stack may remain free standing in any such place or may be removably or permanently secured in any such enclosed space or safe room as described herein. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Summary:
In one embodiment, the present invention provides a free-standing handgun stack for storing multiple handguns in a single column vertical stacking arrangement. In another embodiment the invention provides a handgun stack for storing multiple handguns in a single column vertical stacking arrangement wherein the handgun stack is retrofitable or inserted for permanent or removable attachment to the inside of a gun safe. In one aspect of this embodiment, the gun stack is configured to a height and width that takes up about the same amount of space as a long gun if such long gun were disposed or secured in a vertical position in the same space within the gun safe.