Patent Publication Number: US-11656057-B2

Title: Butt stock for handgun

Description:
RELATED APPLICATION 
     The present application gains priority from Israel patent 263981 filed 26 Dec. 2018, which is included by reference as if fully set-forth herein. 
     FIELD AND BACKGROUND OF THE INVENTION 
     The invention, in some embodiments, relates to the field of handguns, and more particularly but not exclusively, to a butt stock that is reversibly attachable to a handgun, the butt stock having two states: a deployed state and a compact state. 
     Handguns are relatively inaccurate and have a limited effective range in part because these are fired with only two points of contact, the two hands on the grip. This is in contrast with a long gun such as a military rifle which is typically fired with at least four points of contact: a hand on the grip, a hand on the lower hand guard, cheek on the top of the stock and shoulder against the proximal end of the stock. 
     There exist devices that function as accessories allowing a handgun to be fired with more than two points of contact allowing more accurate fire. 
     One example of such a device is the Roni® pistol carbine conversion, a frame in which a handgun is locked, forming a total of four contact points as in a long gun. The large size of such pistol carbine conversions is a disadvantage for some uses. 
     Alternative such devices include the GLR-17 or GLR-440 tactical stocks (FAB Ltd., Modi&#39;in, Israel) which are reversibly attachable to a handgun in tactical situations to form a total of three or four contact points and are collapsible to a state having a relatively small size. However, even in a collapsed state such stocks are too large to conveniently carry when not in use. 
     It would be useful to have a butt stock (also called stock, buttstock, gunstock, or shoulder stock) that is reversibly attachable to a handgun, preferably under tactical conditions. Such a butt stock would advantageously have one or more advantages over the examples cited above, for example, having a state where the butt stock is more compact than the examples cited above. 
     SUMMARY OF THE INVENTION 
     Some embodiments of the invention relate to a butt stock that is reversibly attachable to a handgun, the butt stock having a compact state and a deployed state. The butt stock is relatively compact when in the compact state, but when attached to a handgun in a deployed state may provide multiple points of contact that potentially increase the accuracy of the handgun. 
     According to an aspect of the invention, there is provided a butt stock reversibly attachable to a handgun, comprising: 
     a. a telescopic assembly, comprising:
         a telescoping axis comprising at least two telescopic components: a proximal bar constituting a proximal portion of the telescopic assembly, and a distal bar physically associated with the proximal bar to telescope relative to the proximal bar in the direction of the telescoping axis, and, an adaptor attached to the distal bar, the adaptor configured for reversibly attaching the butt stock to a handgun;       

     b. a quadrilateral assembly comprising:
         a proximal bar, a butt, a first hinge movably connecting the butt to the proximal bar, a cheek rest, a second hinge movably connecting the cheek rest to the butt, a locking bar, a third hinge movably connecting the locking bar to the cheek rest, a fourth hinge movably connecting the locking bar to the proximal bar and a butt axis passing through the rotation axis of the first hinge and the second hinge;
 
the quadrilateral assembly constituting a planar quadrilateral four-bar linkage;
 
the butt stock having at least two states:
   i. a deployed state (also called unfolded or open state) wherein the telescopic assembly is in an extended conformation and the quadrilateral assembly is in an open position,   ii. a compact state (also called folded, closed or collapsed state) wherein the telescopic assembly is in a contracted conformation and the quadrilateral assembly is in a closed position,
 
wherein when the butt stock is in the deployed state and attached to a handgun, the cheek rest is configured to serve as a contact point for the cheek and the butt is configured to serve as a contact point for the shoulder of a user of the handgun.
       

     A butt stock according to the teachings herein comprises a quadrilateral assembly that constitutes a planar quadrilateral four-bar linkage, having four bars movably connected by four hinges, as known in the art the hinges being revolute joints that allow one-degree of freedom: mutual rotation of two connected bars. 
     In preferred embodiments, such as in the exemplary embodiment 10 depicted in the Figures, the quadrilateral assembly constitutes a planar parallelogram four-bar linkage, wherein: in the deployed state the telescopic assembly is in an extended conformation and the quadrilateral assembly is in an open position wherein the four inner angles of the quadrilateral are between 45° and 135°, and in the compact state the telescopic assembly is in a contracted conformation and the quadrilateral assembly is in a closed position wherein two inner angles of the quadrilateral are less than 30° (and the other two inner angles are greater than 150°). As known in the art, in a planar parallelogram four-bar linkage opposing internal angles of the quadrilateral are always equal, the length of opposing sides as defined by the hinge-hinge distance are always equal in lengths, the butt is always parallel to the locking bar, and the proximal bar is always parallel to the check rest. 
     In some embodiments, such as the exemplary embodiment 10 described with reference to the figures, the adaptor is attached to the distal end of the distal bar. 
     In some embodiments, in the open position of the quadrilateral assembly the four inner angles of the quadrilateral are between 60° and 120°, between 70° and 110°, between 80° and 100° and in some embodiments between 85° and 95°. In some preferred embodiments, such as the exemplary embodiment 10, in the open position of the butt stock the four inner angles of the quadrilateral are 90°. 
     In some embodiments, such as the exemplary embodiment 10, the two inner angles of the quadrilateral that are less than 30° in the closed position of the quadrilateral assembly are the angles defined by butt, second hinge, cheek rest and by locking bar, fourth hinge, proximal bar. 
     In some embodiments, in the closed position of the quadrilateral assembly, two inner angles of the quadrilateral are less than 20° (and the other two inner angles are greater than) 160°, are less than 15° (and the other two inner angles are greater than 165°), and in some embodiments are less than 5° (and the other two inner angles are greater than 175°). In some preferred embodiments, such as the exemplary embodiment 10, in the closed position of the quadrilateral assembly two inner angles of the quadrilateral are 0° and the other two inner angles are 180°). 
     In some embodiments, the bars of the telescopic assembly are coaxial, i.e., the proximal bar and the distal bar, and other bars of the telescopic assembly when present, are coaxial. In the exemplary embodiment 10, all three bars of the telescopic assembly (distal bar, middle bar, proximal bar) are coaxial. 
     In some embodiments, such as in the exemplary embodiment 10, any two adjacent bars of the telescopic assembly are directly associated without an intervening component and are configured during extension or retraction to slide one along the other. Some such embodiments have the advantages of being cheap, simple, reliable and/or compact. In some alternative embodiments, in the interface between one or more pairs of adjacent bars of the telescopic assembly are found intervening components, for example, bearings and the like. 
     In some embodiments, in the contracted conformation of the telescopic assembly a majority of the distal bar is inside the proximal bar. In some embodiments, a majority is more than 50%, more than 60%, more than 70%, more than 80% and even more than 90% of the length of the distal bar being contained inside the proximal bar. In the exemplary embodiment 10, in the contracted conformation of the telescopic assembly more than 90% of the length of the distal bar is inside the proximal bar. 
     In some embodiments, the telescopic assembly comprises only two telescoping components, the proximal bar and the distal bar. In some preferred such embodiments, in the contracted conformation the majority of the distal bar is inside the proximal bar. 
     In some embodiments, such as in the exemplary embodiment 10, the telescopic assembly comprises only three telescoping components, the proximal bar, the distal bar and a middle bar located between the proximal bar and the distal bar. In preferred such embodiments, such as in the exemplary embodiment 10, in the contracted conformation the majority of the distal bar is inside the middle bar and a majority of the middle bar is inside the proximal bar. In some such embodiments, such as in the exemplary embodiment 10, in the contracted conformation of the telescopic assembly: a majority of the distal bar is inside the middle bar and the proximal bar; and a majority of the middle bar is inside the proximal bar. 
     In some embodiments, the telescopic assembly comprises at least four telescoping components, the proximal bar, the distal bar and at least two middle bars telescopically located between the proximal bar and the distal bar. In preferred such embodiments, in the contracted conformation the majority of the distal bar is inside a distal-most middle bar and the majority of proximal-most middle bar is inside the proximal bar. 
     In some embodiments having three or more telescoping components, such as in the exemplary embodiment 10, the butt stock further comprises a distal telescope locking mechanism that prevents the distal bar from telescoping to a contracted conformation relative to a preceding middle bar unless the distal telescope locking mechanism is released. In some such embodiments, such as the exemplary embodiment 10, the distal telescope locking mechanism comprises a component that, as a result of a middle bar being telescoped to a contracted conformation relative to the proximal bar, the distal telescope locking mechanism is released, allowing the distal bar to telescope to a contracted conformation relative to a more proximal middle bar. In the exemplary embodiment 10, the distal telescope locking mechanism includes a telescope locking pin, a guide lip and telescoping locking hole: when the middle bar is telescoped to a contracted conformation relative to the proximal bar, the telescope locking pin is pressed into the telescoping locking hole by the guide lip, thereby releasing the distal telescope locking mechanism so that the distal bar can telescope to a contracted conformation relative to the middle bar. 
     In some embodiments, such as in the exemplary embodiment 10, the butt stock further comprises a rotation-locking mechanism that prevents the quadrilateral assembly in the open position from closing to the closed position unless the rotation-locking mechanism is released (e.g. by a user). In preferred embodiments, such as in the exemplary embodiment 10, the rotation-locking mechanism is configured so that recoil of a handgun attached to the butt stock through the adaptor enhances the rotation-locking rather than weakens such locking. In some embodiments, such as in the exemplary embodiment 10, the rotation-locking mechanism comprises a locking component that is ordinarily biased to a locked position preventing rotation of the proximal bar relative to the butt, the locking component configured to be moved by a user to an unlocked position where rotation of the proximal bar relative to the butt is not prevented. In the exemplary embodiment 10, the rotation-locking mechanism includes rotation locking pins, rotation locking holes in the butt and rotation locking holes in the proximal bar, the rotation locking pins biased by a spring to a locked position that prevents rotation of the proximal bar relative to the butt. 
     In some embodiments, such as in exemplary embodiment 10, the butt stock further comprises a proximal telescoping locking mechanism that prevents the telescopic assembly in the extended conformation from retracting to the retracted conformation unless the proximal telescoping locking mechanism is released. 
     In some embodiments, such as in exemplary embodiment 10, the butt stock comprises a proximal telescoping locking mechanism that prevents the telescopic assembly in the extended conformation from retracting to the retracted conformation unless the proximal telescoping locking mechanism is released, the proximal telescoping locking mechanism configured so that: 
     when the quadrilateral assembly is locked in the open configuration, the proximal telescoping locking mechanism prevents the telescopic assembly in the extended conformation from retracting to the retracted conformation; and 
     when the quadrilateral assembly is at least partially moved from the open configuration, the proximal telescoping locking mechanism does not prevent the telescopic assembly in the extended conformation from retracting to the retracted conformation. In some such embodiments, such as in the exemplary embodiments 10, the proximal telescoping locking mechanism comprises a locking tooth physically associated with the locking bar and a proximal gap in a bar most proximal to the proximal bar (in exemplary embodiment 10, a middle bar), so that: 
     when the quadrilateral assembly is locked in the open configuration, the locking tooth is located inside the proximal gap, preventing axial movement of the bar most proximal relative to the proximal bar; and 
     when the quadrilateral assembly is not locked in the open configuration, the locking tooth is not located inside the proximal gap. 
     In some embodiments, such as in exemplary embodiment 10, the butt stock is configured so that in the compact state, the adaptor is attachable to and detachable from a handgun. 
     In some embodiments, such as in exemplary embodiment 10, the adaptor is configured for reversibly attaching the butt stock to a handgun by reversibly mating with an integral part of a handgun. 
     Additionally or alternatively, in some embodiments the adaptor is configured for reversibly attaching the butt stock to a handgun by reversibly mating with a mating component that is separately attached to the handgun. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Some embodiments of the invention are herein described with reference to the accompanying figures. The description, together with the figures, makes apparent to a person having ordinary skill in the art how some embodiments of the invention may be practiced. The figures are for the purpose of illustrative discussion and no attempt is made to show structural details of an embodiment in more detail than is necessary for a fundamental understanding of the invention. For the sake of clarity, some objects depicted in the figures may not be to scale. 
       In the Figures: 
         FIG.  1    depict an exemplary embodiment of a butt stock according to the teachings herein in  FIG.  1 A  in a deployed state attached to a handgun, in  FIG.  1 B  in a deployed state held for use in hand-to-hand combat, in  FIG.  1 C  in a compact state held for use as a hammer, for example, for breaking a glass window and in  FIG.  1 D  in an intermediate state (where the quadrilateral assembly is in a closed position and the telescopic assembly is in an at least partially extended conformation) for use as a hammer, for example for breaking a glass window; and 
         FIGS.  2 A- 2 U  schematically depict the exemplary embodiment of a butt stock according to the teachings herein in various views during various steps of changing from a deployed state to a compact state. 
     
    
    
     DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION 
     Some embodiments of the invention relate to a butt stock that is reversibly attachable to a handgun, the butt stock having a compact state and a deployed state. The butt stock is relatively compact when in the compact state, but when attached to a handgun in a deployed state may provide multiple points of contact for a user of the handgun that potentially increase the accuracy of the handgun. In the compact state the butt stock is relatively compact, in some but not all embodiments sufficiently compact to fit in a conventional pistol magazine pouch. 
     In some, but not all, embodiments, the butt stock is easily attachable to a handgun, even under tactical conditions. In some, but not all, embodiments, the butt stock is easily deployable, that is to say, the butt stock can easily be changed from the compact state to the deployed state. In some, but not all, embodiments, the butt stock is easily detachable from a handgun, especially under tactical conditions. In some, but not all, embodiments, the butt stock can easily be changed from the deployed state to the compact state. 
     As used herein, the term tactical conditions is as understood by a person having ordinary skill in the art and typically includes conditions where a user of the butt stock is under time constraints, possibly under conditions of limited visibility (e.g., dark), must maintain situational awareness including paying attention to electronic, verbal or gesture communications, is possibly moving or taking cover and may be under fire or believing that there is an imminent possibility of being under fire. 
     The principles, uses and implementations of the teachings of the invention may be better understood with reference to the accompanying description and figures. Upon perusal of the description and figures present herein, one skilled in the art is able to implement the teachings of the invention without undue effort or experimentation. In the figures, like reference numerals refer to like parts throughout. 
     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth herein. The invention is capable of other embodiments or of being practiced or carried out in various ways. The phraseology and terminology employed herein are for descriptive purpose and should not be regarded as limiting. 
     A preferred exemplary embodiment of a butt stock according to the teachings herein is depicted in the Figures. 
     In  FIG.  1 A , an embodiment of a butt stock  10  according to the teachings herein is depicted in a deployed state attached to an exemplary handgun  12  (a Glock 19) through an adaptor  14  that reversibly locks into a gap in a grip  16  of handgun  12  just behind a magazine well  18 , similar to an adaptor used in the commercially-available GLR-17 or GLR-440 tactical stocks (FAB Ltd., Modi&#39;in, Israel). 
     In  FIG.  1 B , butt stock  10  is depicted in a deployed state, held in a hand  20  of a user for use in hand-to-hand combat in a manner analogous to brass knuckles. 
     In  FIG.  1 C , butt stock  10  is depicted in a compact state, held in hand  20  for use as a hammer, for example, for breaking a glass window. 
     In  FIG.  1 D , butt stock  10  is depicted in an intermediate state (where the quadrilateral assembly is in a closed position and the telescopic assembly is in an at least partially extended conformation) for use as a hammer, for example for breaking a glass window. 
       FIGS.  2 A- 2 U  schematically depict various views of butt stock  10  during the process of changing from the deployed state depicted in  FIGS.  1 A and  1 B  to the compact state as depicted in  FIG.  1 C . 
       FIG.  2 A : Deployed State 
     In  FIG.  2 A , collapsible butt stock  10  is depicted in the deployed state. From left (distal) to right (proximal) are seen adaptor  14 , a distal bar  22 , a hollow middle bar  24 , a hollow proximal bar  26  and a butt  28 . Connected to butt  28  is a cheek rest  30 . Linking cheek rest  30  to proximal bar  26  is a locking bar  32 . 
     An imaginary telescoping axis  34  passes through the centers of distal bar  22 , middle bar  24  and proximal bar  26 . Distal bar  22  is configured to telescopically slide into the hollow of middle bar  24  and middle bar  24  is configured to telescopically slide into the hollow of proximal bar  26  along telescoping axis  34 . 
     Telescoping axis  34  and an imaginary butt axis  36  are included in and define a vertical plane of butt stock  10  which substantially bisects the above-listed physical components. When butt stock  10  is in the deployed state, butt axis  36  is perpendicular to telescoping axis  34 . 
     Proximal bar  26  is connected to butt  28  through a hinge  38  allowing rotation of proximal bar  26  relative to butt  28  around the rotation axis of hinge  38  which rotation axis is perpendicular to the vertical plane. Butt  28  defines a hollow in which the proximal end of proximal bar  26  is held, proximal bar  26  having a width dimension (parallel to the rotation axis of hinge  38 ) that is smaller than the hollow of butt  28 . Further, the rotation axis of hinge  38  is offset distally from the proximal end of butt  28  by a distance that is at least a little greater than the height of proximal bar  26 , the height being the dimension perpendicular to telescoping axis  34  and the rotation axis of hinge  38 . As a result and as discussed in greater detail below, when proximal bar  26  is rotated around hinge  38  during a change of butt stock  10  from a deployed state to a compact state (proximal bar  26  moving counter clockwise relative to butt axis  36  in  FIG.  2 A ), proximal bar  26  enters the hollow of butt  28 . 
     A proximal end of cheek rest  30  is connected to butt  28  through a hinge  40  allowing rotation of check rest  30  relative to butt  28  around the rotation axis of hinge  40  that is perpendicular to the vertical plane. As noted above, butt  28  defines a hollow in which the proximal end of cheek rest  30  is held, cheek rest  30  having a width dimension (parallel to the rotation axis of hinge  40 ) that is smaller than the hollow of butt  28 , 
     An upper end of locking bar  32  is connected to cheek rest  30  through a hinge  42  allowing rotation of locking bar  32  relative to cheek rest  30  around a rotation axis of hinge  42  perpendicular to the vertical plane. Cheek rest  30  defines a hollow in which an upper end of locking bar  32  is held, locking bar  32  having a width dimension (parallel to the rotation axis of hinge  42 ) that is smaller than the hollow of locking bar  32 . 
     A lower end of locking bar  32  is connected to proximal bar  26  through a hinge  44  allowing rotation of locking bar  32  relative to proximal bar  26  around a rotation axis of hinge  44  perpendicular to the vertical plane. 
     Proximal bar  28 , hinge  38 , butt  28 , hinge  40 , cheek rest  30 , hinge  42 , locking bar  32  and hinge  44  together define a planar quadrilateral four-bar linkage which is a planar parallelogram four-bar linkage where the length of opposing linkages is the same, i.e., the distance between the axes of hinges  38 - 40  is equal to the distance between the axes of hinges  42 - 44  and the distance between the axes of hinges  40 - 42  is equal to the distance between the axes of hinges  38 - 40 . 
     The head of a rotation locking pin  45  is seen on the side of butt  28  which function is discussed in detail hereinbelow. The head of a telescoping locking pin  47  is seen protruding from the bottom of middle bar  24  near the distal end thereof, which function is discussed in detail hereinbelow. 
     In  FIG.  2 A , adaptor  14  is seen from the side, comprising a locking head  46  and a release button  48 . As noted above, adaptor  14  is similar or identical to an adaptor used in commercially-available GLR-17 or GLR-440 tactical stocks (FAB Ltd., Modi&#39;in, Israel). For attaching butt stock  10  to a Glock 19 handgun, locking head  46  is pushed into the gap behind the magazine well of the handgun. Locking head  46  is biased to a locking position so, when pushed fully into the gap, locks into place. To separate butt stock  10  from a handgun, a user presses release button  48  so that locking head  46  is in a released confirmation and is easily pulled out of the gap. 
     
       FIG.  2 B 
     
     In  FIG.  2 B , the intersection of middle bar  24 , proximal bar  26  and locking bar  32  around hinge  44  is shown in greater detail. Also seen in  FIG.  2 B  is a guide lip  50  that will be discussed in detail hereinbelow. 
     
       FIG.  2 C 
     
     In  FIG.  2 C , a cut-out view of the intersection of middle bar  24 , proximal bar  26  and locking bar  32  is depicted. 
     In  FIG.  2 C  it is seen how locking bar  32  is attached to proximal bar  26  with a hinge  44  which limits the movement of locking bar  32  relative to proximal bar  26  to only rotation around the axis of hinge  44  in the vertical plane. 
     Also seen in  FIG.  2 C  is that in the deployed state of butt stock  10 , a locking tooth  52  which is an integrally formed portion of locking bar  32  passes through a distal gap  54  in the top of proximal bar  26  and a proximal gap  56  in the top of middle bar  24 . Locking tooth  52  thereby locks the relative position of proximal bar  26  to middle bar  24  and prevents telescopic contraction of middle bar  24  into the hollow of proximal bar  26  when butt stock  10  is in an open position. 
     Also seen in  FIG.  2 C  is a slide pin  58  attached to and protruding from middle bar  24  into a groove  60  in the bottom inner face of proximal bar  26 : slide pin  58  is configured to snugly fit in groove  60 , allowing telescopic motion (extension and contraction) along telescoping axis  34  of middle bar  24  into and out of proximal bar  26 , but reducing or preventing rotational motion of middle bar  24  relative to proximal bar  26  around telescoping axis  34 . 
     
       FIG.  2 D 
     
       FIG.  2 D  is a cut-out view of the rotation-locking mechanism that prevents unwanted change of butt stock  10  from the deployed state to the compact state and collapse of the quadrilateral assembly from the open position to the closed position by preventing rotation around hinge  38  of proximal bar  26  relative to butt  28  unless the rotation-locking mechanism is released. The rotation-locking mechanism is fixed to proximal bar  26  and includes two opposing convex-headed rotation locking pins  45  outwardly biased with a coil spring  62 , coil spring  62  and the two locking pins  45  held inside a retention tube  64  which inner bore is dimensioned to snugly slidingly contains locking pins  45  allowing axial sliding of locking pins  45 . In the deployed state of butt stock  10 , coil spring  62  pushes locking pins  45  outwards so that a ridge  66  of locking pins  45  is pressed against inner surfaces of proximal bar  26 , through rotation locking holes  68  in proximal bar  26  and into rotation locking holes  70  in butt  28 . The outer diameter of locking pins  45  and inner diameter of locking holes  68  and  70  are such that there is no substantial rotational motion of proximal bar  26  relative to butt  28  around hinge  38  when locking pins  45  are located inside locking holes  70  in butt  28 . In the deployed state of butt stock  10 , the convex heads of locking pins  45  pass through the walls of proximal bar  26  and butt  28  to protrude into recesses  72  in the outer side faces of butt  28  but do not protrude beyond the outer side faces of butt  28 . 
     
       FIG.  2 E 
     
     In  FIG.  2 E , the intersection of proximal bar  26  and butt  28  is depicted, with the convex heads of locking pins  45  protruding into recesses  72  in the outer side faces of butt  28 . 
     Deployed State to Compact State—Release of Locking Tooth 
     When a user wants to change butt stock  10  from a deployed state to a collapsed state, the user first simultaneously pushes both locking pins  45  inwardly against the force applied by coil spring  62 , e.g., with a thumb and opposing finger, see  FIGS.  2 D and  2 E . When locking pins  45  are pushed inwardly at least to the extent that at least some of the convex part of the heads of locking pins  45  is located inside rotation locking holes  68  in proximal bar  26 , the user applies a force to rotate proximal bar  26  relative to butt  28  around hinge  38 . Such rotation moves the convex part of the heads of locking pins  45  out of rotation locking holes  70  in butt  28  so that locking pins  45  no longer prevent rotation of proximal bar  26  relative to butt  28  around hinge  38 . 
     In  FIG.  2 F , the intersection of proximal bar  26  and butt  28  is depicted during collapse of butt stock  10  from deployed state where proximal bar  26  is rotated relative to butt  28  around hinge  38 . In  FIG.  2 F , retention tube  64  is depicted cut-out, 
     As is seen in  FIG.  2 F , no part of locking pins  45  is located inside rotation locking holes  70  in butt  26  and the convex heads of locking pins  45  are pressed against an inner surface of butt  28 , compressing coil spring  62  so that ridges  66  of locking pins  45  do not contact proximal bar  26 . 
     In  FIG.  2 G  (compare to  FIG.  2 D ), a cut out view of the intersection of proximal bar  26  and butt  28  is depicted, subsequent to the depicted in  FIG.  2 F  after rotation of proximal bar  26  relative to butt  28  in the vertical plane around hinge  38  so that the quadrilateral assembly of butt stock  10  is partially collapsed. As a result, the convex heads of locking pins  45  can no longer pass through rotation locking holes  70  in butt  28  and the heads of locking pins  45  are pressed by coil spring  62  against an inner surface of butt  28 . Importantly, butt  28  is dimensioned (especially in the depth dimension which in  FIG.  2 A  is perpendicular to butt axis  36  and parallel to telescoping axis  34 ) that throughout the rotation of proximal bar  26  relative to butt  28  around hinge  38 , the convex heads of locking pins  45  are pressed by coil spring  62  against an inner surface of butt  28 . 
     In  FIG.  2 H , a side view of butt stock  10  is depicted wherein the quadrilateral assembly is in a partially collapsed state corresponding to  FIG.  2 G . Locking bar  32  and butt  28  are both rotated in the vertical plane relative to proximal bar  26  and cheek rest  30  so that in side view the parallelogram four-bar linkage defined by cheek rest  30 , hinge  40 , butt  28 , hinge  38 , proximal bar  26 , hinge  44 , locking bar  32  and hinge  42  has the shape of a rhomboid parallelogram as opposed to a right parallelogram (rectangle) as depicted in  FIG.  2 A  in the fully deployed state of butt stock  10 . Further, telescoping axis  34  and butt axis  36  are no longer perpendicular although both still are within the vertical plane of butt stock  10 . As discussed above, locking pins  45  cannot protrude through locking holes  70  of butt  28 . Importantly, as a result of the rotation around hinges  38 ,  40 ,  42  and  44 , locking tooth  52  of locking bar  32  is withdrawn from and located outside of distal gap  54  in the top of proximal bar  26  and proximal gap  56  in the top of middle bar  24 , so that the position of proximal bar  26  relative to middle bar  24  is no longer locked. 
     In  FIG.  2 I  (compare to  FIGS.  2 B and  2 C ), a close up perspective view of the intersection of proximal bar  26 , middle bar  24  and locking bar  32  of butt stock  10  is depicted where the quadrilateral assembly is in a partially collapsed state corresponding to  FIGS.  2 G and  2 H , providing greater detail of how locking tooth  52  of locking bar  32  is outside of distal gap  54  in the top of proximal bar  26  and proximal gap  56  in the top of middle bar  24 . Also seen is guide lip  50  extending from the bottom surface of proximal bar  26 . 
     With reference to  FIGS.  2 G,  2 H and  2 I , once locking tooth  52  is outside of distal gap  54  in the top of proximal bar  26  and proximal gap  56  in the top of middle bar  24 , a user can telescopically contracti middle bar  24  into proximal bar  26  in the usual way. 
     Deployed State to Compact State—Release of Telescoping Locking Pin 
     In  FIG.  2 J , a close up perspective view from the bottom of the intersection of distal bar  22  and middle bar  24  is depicted. The convex head of telescoping locking pin  47  is seen protruding through telescoping locking hole  74  from the bottom side of middle bar  24  near the distal end thereof. 
     In  FIG.  2 K , a side cross section equivalent to  FIG.  2 J  is shown. Telescoping locking pin  47  is seen contained inside a hollow  76  in the bottom of distal bar  22 , biased downwards by a coil spring  78 , to protrude through telescoping locking hole  74  through the bottom of middle bar  24 , thereby preventing any telescopic movement of distal bar  22  into middle bar  24 . 
     As noted above with reference to  FIGS.  2 G,  2 H and  2 I , once locking tooth  52  is outside of distal gap  54  in the top of proximal bar  26  and proximal gap  56  in the top of middle bar  24 , middle bar  24  can be telescopically contracted into proximal bar  26 , that is to say, a user can push middle bar  24  in the direction of telescoping axis  34  into the hollow of proximal bar  26 . 
     With reference to  FIGS.  2 L,  2 M,  2 N and  20   , the telescopic contraction of middle bar  24  into proximal bar  26  eventually brings the convex head of telescoping locking pin  47  into contact with the inner surface of guide lip  50 . As seen in  FIGS.  2 L,  2 M,  2 N and  20   , as middle bar  24  and proximal bar  26  are telescopically contracted, contact of the convex head of telescoping locking pin  47  with the inner surface of guide lip  50  forces telescoping locking pin  47  upwards into hollow  76  in distal bar  22  while compressing coil spring  78 . When telescoping locking pin  47  is pushed far enough into hollow  76 ,  FIG.  2 N , telescoping locking pin  47  no longer prevents distal bar  22  from sliding into the hollow of middle bar  24 . Further force applied by a user telescopically contracts distal bar  22  into middle bar  24  while spring  78  remains compressed and the convex head of telescoping locking pin  47  is pressed and slides along against an inner surface of middle bar  24 . 
     Deployed State to Compact State—Collapsing the Quadrilateral Assembly 
     With reference to  FIGS.  2 P and  2 Q , the user continues pushing distal bar  22  in a proximal direction towards butt  28 , e.g., with the palm of the left hand. 
     As a result, the force applied by the user slides distal bar  22  into middle bar  24  until complete telescopic contraction which length is dictated by the length and details of construction of distal bar  22  and of middle bar  24  where a majority of distal bar  22  is located inside the hollow of middle bar  24 , see  FIG.  2 Q . 
     Further, the force applied by the user slides middle bar  24  into proximal bar  26  until complete telescopic contraction which length is dictated by the length and details of construction of middle bar  24  and of proximal bar  26  where a majority of middle bar  24  is located inside the hollow of proximal bar  26 , see  FIG.  2 Q . 
     Independently of the telescopic contraction of the telescopic assembly of butt stock  10 , which comprises distal bar  22 , middle bar  24  and proximal bar  26 , caused by the user pushing distal bar  22  in a proximal direction, the user also forces cheek rest  30  and butt  28  together, e.g., by closing the right hand around these two components, thereby collapsing the quadrilateral assembly comprising proximal bar  28 , hinge  38 , butt  28 , hinge  40 , cheek rest  30 , hinge  42 , locking bar  32  and hinge  44 . By “collapsing” is meant that two of the four opposing angles of the quadrilateral are made progressively more acute, e.g., in butt stock  10  the angle defined by butt  28 , hinge  40  and cheek rest  30  and the angle defined by proximal bar  26 , hinge  44  and locking bar  32 . Further, the progressive collapsing changes the angle between telescoping axis  34  and butt axis  36  to be progressively further from perpendicular. 
     The Compact State 
     Butt stock  10  is depicted in the compact state in  FIG.  2 Q  (side view),  FIG.  2 R  (viewing from the distal end in a proximal direction),  FIG.  2 S  (viewing from the proximal end in a distal direction),  FIG.  2 T  (view from the bottom at cheek rest  30 ) and  FIG.  2 U  (view from the top at butt  28 ). In  FIG.  2 U , retention tube  64  is depicted as transparent allowing rotation locking pins  45  and coil spring  62  to be seen. 
     From  FIGS.  2 Q- 2 U  a number of features of butt stock  10  in the compact state are seen. 
     Adaptor 
     In the compact state of butt stock  10 , adaptor locking head  46  is clear of obstruction and accessible, allowing attachment and detachment of butt stock  10  to a handgun even when butt stock  10  is in a compact state. 
     Telescoping Axis 
     In the compact state, telescoping axis  34  and butt axis  36  are within 5° of parallel (in butt stock  10 , ±1° of parallel). In some alternative embodiments, in the compact state the telescoping axis and the butt axis are within 30°, within 20°, within 10° and even within 5° of parallel. Generally, the closer to parallel the two axes are, the more compact the butt stock is in the compact state and therefore typically is more preferred. 
     Configuration and Dimensions of Telescopic Assembly 
     In the compact state of butt stock  10  described above, distal bar  22  and middle bar  24  are both dimensioned and configured so that more than 90% of the length of distal bar  22  is contained inside middle bar  24  when fully retracted thereinto. In some alternative embodiments, in the compact state the distal bar and middle bar are dimensioned and configured that more than 50%, more than 60%, more than 70%, more than 80% and even more than 90% of the length of the distal bar is contained inside the middle bar when fully retracted thereinto. 
     In the compact state of butt stock  10  described above, middle bar  24  and proximal bar  26  are both dimensioned and configured so that more than 90% of the length of middle bar  24  is contained inside proximal bar  26  when fully retracted thereinto. In some alternative embodiments, in the compact state the middle bar and proximal bar are dimensioned and configured that more than 50%, more than 60%, more than 70%, more than 80% and even more than 90% of the length of the middle bar is contained inside the proximal bar when fully retracted thereinto. 
     Configuration and Dimensions of Butt 
     In butt stock  10 , butt  28  is dimensioned and configured to constitute an open ended trough that in the compact state contains the telescoping components of butt stock  10 . Such dimensioning and configuration includes that the width between the inner faces of the walls of butt  28  are greater than the width of proximal bar  26 , that the depth of the trough of butt  28  is deeper than the height of proximal bar  26 , that hinge  38  is located at the top edges of both butt  28  and proximal bar  26 . Importantly, the length of butt  28  (parallel to butt axis  36 ) from hinge  38  is sufficient to contain most of the telescoping assembly with only a small portion of adaptor  14  not enclosed allowing access to adaptor release button  48  when butt stock  10  is in a compact state, see  FIG.  2 Q . In some embodiments, the butt is even longer, for example, even to extending far enough to enclose all of the adaptor. In some embodiments, the distal end of the butt (the part that in the compact state of the butt stock is closest to the adaptor extends upwards in a direction perpendicular to the butt axis to cover at least some of the sides of the adaptor. In some embodiments, the distal end of the butt includes a wall that covers some or all of the adaptor from the axial direction. 
     In butt stock  10 , in the compact state the distal portion of the telescopic assembly can be seen, see  FIG.  2 Q . In some alternate embodiments, the walls of the butt are higher, for instance along the entire length of the butt, shielding more of the telescoping assembly from view than in butt stock  10  when in the compact state and even entirely shielding the telescoping assembly from view when in the compact state. 
     Configuration and Dimensions of Cheek Rest 
     In butt stock  10 , cheek rest  30  is trough-shaped and locking bar  32  is sufficiently narrow along most of the length to fit inside the trough of cheek rest in the compact state, the exception being near locking tooth  52  where locking bar  32  has a width that is substantially the same as that of cheek rest  30 . As a result, in the compact state, the portion of locking bar  32  near locking tooth  52  is visible, see  FIG.  2 T . In some alternative embodiments, the locking bar is sufficiently narrow along the entire length to fit in the trough of the cheek rest. In some such embodiments, the cheek rest is longer than as depicted in butt stock  10 , for example, in some embodiments covering all of the locking bar, and in some embodiments even further, for example close to or even contacting the adaptor. 
     Configuration of Cheek Rest 
     In butt stock  10 , cheek rest  30  is narrower than the width between the inner faces of the walls of butt  28 . As a result, in the compact state butt stock  10  has a stepped cross section, see  FIG.  2 T  where the rims of the walls of butt  28  are visible next to cheek rest  30 . As a result, in the compact state the rims of the walls of cheek rest  30  are located inside the trough of butt  28 . The step in the cross section caused by the difference in width is not significant, so that in cross section in the compact state butt stock  10  is approximately a round-edged rectangle that can be comfortably held, see  FIG.  1 C . 
     In some alternate embodiments, the width of the cheek rest is substantially equal or identical to the width of the butt, one exception being the flanges that are part of the hinges. As a result, in some such embodiments the butt and the cheek rest together constitute a partial clam shell package of the butt stock so in the compact state the edges of the butt and the cheek rest are in contact. 
     In some alternate embodiments, the cheek rest is wider than the butt and, in the compact state, portions of the butt are contained within the trough of the cheek rest. 
     Extension/Retraction of the Telescopic Assembly 
     As discussed above, a characteristic of some embodiments of a butt stock such as butt stock  10  is that locking the quadrilateral assembly in the open position requires that middle bar  24  be fully extended out of proximal bar  26 , allowing locking tooth  52  of locking bar  32  to enter proximal gap  56  in middle bar  24 . If middle bar  24  is not fully extended, locking tooth  52  cannot enter proximal gap  56  so that hinges  38 ,  40 ,  42  and  44  cannot rotate to a fully open position. Once middle bar  24  is fully extended and locking tooth  52  enters proximal gap  56 , subsequent retraction of middle bar  24  into proximal bar  26  is not possible, allowing the telescoping assembly to remain in the extended conformation even when an attached handgun is fired and the consequent recoil applies a substantial force in the proximal direction through the telescoping assembly along telescoping axis  34 . 
     However, some embodiments, of a butt stock according to the teachings herein, such as butt stock  10 , are configured to allow extension and retraction of some or all of the telescopic assembly when the butt stock is in the compact state and the parallelogram assembly is in the closed position. For example, from the compact state of butt stock  10  as depicted in  FIGS.  1 C and  2 Q , a user grips the closed-position quadrilateral assembly in one hand and with the other hand holds adaptor  14  and pulls distally along telescoping axis  34 . Distal bar  22  is pulled out of middle bar  24  until telescoping locking pin  47  of distal bar  22  passes through telescoping locking hole  74  of middle bar  24 , thereby locking distal bar  22  in an extended conformation relative to middle bar  24 . Concurrently, middle bar  24  is pulled out of proximal bar  26  until fully extended relative to proximal bar  26 . Although distal gap  54  of proximal bar  26  and proximal gap  56  of middle bar  24  are aligned, as long as the quadrilateral assembly is in the closed position, extension/retraction of middle bar  24  relative to proximal bar  26  is not locked. 
     In such a state, where the telescopic assembly is in an extended conformation while the quadrilateral assembly is in a closed position, butt stock  10  is useable as a hammer, e.g., to break glass windows or as a tool that extends the reach of the user, see  FIG.  1 D . 
     Use of a Butt Stock Such as Butt Stock  10   
     A person having ordinary skill in the art of shooting will understand the operation and use of a butt stock according to the teachings herein by perusal of the above description and the accompanying figures. For the sake of completeness, a specific embodiment of the use of butt stock  10  is described in detail. 
     A right-handed user is carrying a holstered handgun and a butt stock  10  in a compact state in a magazine pouch or clipped to a belt underneath a jacket. Due to the small size of butt stock  10  in the compact state, it is not possible to see the presence of the butt stock. 
     The user perceives a situation that potentially requires accurate fire from the handgun. While moving to a firing position, the user draws the handgun with the right hand and butt stock  10  with the left hand. In a motion similar to loading a magazine into the handgun, the user inserts adaptor locking head  46  into the appropriate gap in the handgun, thereby attaching butt stock  10  to the handgun. While holding the handgun by the grip with the right hand, the user grasps butt  28  (preferably the distal portion that in the compact state is closest to adaptor  14 ) between the thumb and forefinger of the left hand, then pulls the left hand back, thereby changing butt stock  10  from the initial compact state to the deployed state depicted in  FIG.  1 A . The user feels that rotation locking pins  45  pass into rotation locking holes  68  and  70 , ridges  66  being pushed against the inside of proximal bar  26  so that the parallelogram assembly is locked in the open position, and that telescoping locking pin  47  passes through telescoping locking hole  74  so that the telescopic assembly is locked in the extended conformation. 
     The user then lifts the handgun with the right hand and adopts a firing position having 4 points of contact: the right cheek resting on cheek rest  30 , the proximal end of butt  28  pressed into the right shoulder, the right hand holding the handgun grip, while the right index figure rests on the right side of the trigger guard ready to be moved into the trigger guard to pull the trigger if necessary with the left hand encircling the right hand in a manner similar to a Weaver stance. 
     Adaptor 
     In the embodiment depicted above, butt stock  10  includes an adaptor to couple with a handgun. Depicted is adaptor  14  for coupling with a Glock 19 pistol. Different embodiments of the butt stock include suitable different adaptors to couple with different handguns. In some embodiments, an adaptor is a permanent component of the butt stock, in some such embodiments being integrally formed with the distal bar or equivalent component. In some alternate embodiments, the adaptor is replaceable, i.e., is configured to allow simple replacement of one adaptor with another adaptor using a simple tool or tools (e.g., a screw driver or allen wrench) and in some embodiments no tool (e.g., is held in place with a manually-removable pin) allowing a specific butt stock to be used with different types of handguns by replacing the adaptor. 
     Adaptor  14  depicted in the Figures is a dedicated adaptor that fits into an integral part of a Glock 19, the gap in the grip. The advantage of such an adaptor is that the butt stock can be attached to a handgun or detached from a handgun quickly and easily, even in tactical situations. 
     Some handguns do not have a feature that allows such easy attachment/detachment of a butt stock or a user is not interested in such easy attachment/detachment. In some such embodiments, an adaptor of a butt stock is a different type of component. For example, in some embodiments an adaptor comprises a ring configured to surround an integral feature of a handgun such as the grip. In some such embodiments, the adaptor comprises a ring that can be closed around the grip of a handgun, for example, similar in construction and/or operation to a circular clamp or pipe clamp including one or more ring parts that can be closed around the grip or other integral part of a handgun. In some such embodiments, the adaptor comprises a constricting ring similar in construction and/or operation to a tightenable hose clamp including one or more ring parts that can be constricted around the grip or other integral part of a handgun. 
     Alternatively, in some embodiments there is provided a mating component matched to mate with the adaptor, the mating component being separately attachable to a handgun prior to attachment of a butt stock. Such a mating component is dimensioned and configured to mate with a suitable adaptor, allowing simple attachment/detachment of a butt stock provided with the suitable adaptor, preferably even in tactical situations. 
     In butt stock  10 , in the compact state adaptor release button  48  is not associated with any other component of butt stock  10  except for adaptor  14  and the only function of adaptor release button  48  is to release adaptor  14  from attachment to a handgun. In some alternative embodiments, in the compact state of a butt stock, the adaptor release button engages a part of some other component of the butt stock such as the butt and, through a biasing mechanism such as a spring, actively holds the butt stock locked in the compact state. In such embodiments, when the adaptor locking head is attached to a handgun, such attachment releases the engagement of the adaptor release button with the part of the component so that the butt stock can be changed to the deployed state. 
     Attachment Component 
     In some embodiments, a collapsible butt stock according to the teachings herein further comprises an attachment component. In such embodiments, the attachment component allows a user to secure the butt stock when in a compact state to themselves or to another object to help prevent loss of the collapsible butt stock, especially in a tactical situation. 
     In some embodiments an attachment component comprises or is a magnet, e.g., a rare earth magnet, to allow a user to secure the butt stock to a suitable ferromagnetic object, for example, a magazine inside a pouch worn by the user or a dedicated metal plate worn by the user. The modest dimensions and weight of the butt stock allow a magnet to be sufficient to secure the butt stock to a user and to prevent a secured butt stock from interfering with the normal activity of a user. 
     Alternatively or additionally, in some embodiments an attachment component comprises a flat retention clip, e.g., of stainless steel clip, allowing the butt stock to be secured to a user by hanging the butt stock on a belt or webbing where the belt or webbing is located between the retention clip and the butt stock. 
     Alternatively or additionally, in some embodiments an attachment component comprises or is a part of a hook-and-loop fastener, e.g., Velcro®, to allow a user to secure the butt stock to a suitably located opposite part of a hook-and-loop fastener. Typical suitable opposite-part of the hook-and-loop fastener can include such a part of a fasterner that is part of a belt, webbing or vest worn by the user. 
     Alternatively or additionally, in some embodiments an attachment component comprises a lanyard, one end of the lanyard secured to the butt stock and the other end securable to a user or an object worn by the user such as a belt, webbing or vest. In some preferred such embodiments the lanyard is extensible, e.g., comprises a coiled section which length can be varied (analogous to telephone cords from the 1970s) or a wound section on a spring-loaded wheel (similar to a retractable key chain). 
     Retention Tube 
     Butt stock  10  depicted above includes a retention tube  64  to physically contain rotation locking pins  45  and coil spring  62 . Some embodiments of a butt stock according to the teachings herein have an otherwise similar or identical rotation-locking mechanism which is devoid of a retention tube such as  64 . 
     Material 
     A collapsible butt stock according to the teachings herein is made of any suitable material or combination of materials, for example, metals such as aluminum, aluminum alloys, magnesium, magnesium alloys, steel, carbon fiber and polymers. In a prototype made by the inventor, except for the middle bar  24 , all of the structural components of the butt stock (distal bar  22 , proximal bar  26 , butt  28 , cheek rest  30  and locking bar  32 ) were made of fiber-reinforced polymer (e.g., a fiber reinforced polymer such as Nylon or Nylon derivative) known in the art of gun smithing. Middle bar  24  which was made of 1 mm thick aluminum because it was found that using current technology, it was challenging to make a middle bar  24  of fiber-reinforced polymer that was sufficiently compact yet could survive the recoil of repeated firing of an attached handgun. 
     Dimensions 
     It is preferred that a butt stock according to the teachings herein be as compact as possible for one or more reasons. In some embodiments, it is desired that the butt stock be concealable and/or easy to carry in the compact state. On the other hand, the dimensions of the butt stock must be large enough to make the butt stock useful in stabilizing firing of a handgun and robust enough to survive rough handling and repeated recoil. 
     In some embodiments, in the compact state a butt stock according to the teachings herein has a length of 10-20 cm long (dimension parallel to the butt axis), and a width and depth of 2-8 cm, more preferably 2-6 cm (dimensions perpendicular to the length). 
     In a prototype made by the inventor, in the compact state a butt stock  10  had a length of 16 cm, a width of 28 mm (being the width of butt  28  while the width of cheek rest  30  was 20 mm) and a depth of 47 mm. The length of the prototype in the deployed state (the dimension parallel to the telescoping axis  34  including to the tip of the adaptor) was 33 cm. 
     Number of Telescoping Parts 
     In the embodiment depicted in the Figures, butt stock  10  includes a telescopic assembly with three telescoping parts: proximal bar  26 , middle bar  24  and distal bar  22  to connect butt  28  to adaptor  14 . It was found that using current material technology, a three-part telescopic assembly connecting adaptor  14  to butt  28  was preferred to ensure that in a deployed state when attached to a handgun, the handgun/butt distance was sufficient for comfortable and accurate firing while ensuring that the components were sufficiently strong to undergo the recoil of repeated firing of the handgun without damage. 
     In some related embodiments, a butt stock according to the teachings herein includes a telescopic assembly with only two telescopic parts, a proximal bar and a distal bar. Typically but not necessarily, such embodiments have a larger length dimension in the compact state. In such embodiments, preferably but not necessarily, the proximal bar is substantially similar or identical in function and construction as described hereinabove for proximal bar  26  of butt stock  10  and the distal bar is substantially similar or identical in function and construction as described hereinabove for middle bar  24  of butt stock  10 , except that an adaptor is attached to the distal end of the distal bar. 
     In some related embodiments, a butt stock according to the teachings herein includes a telescopic assembly with more than three telescoping parts, e.g., four, five, six or even more telescoping parts. Some such embodiments are expensive due to the components being made of comparatively expensive materials to ensure that the butt stock is sufficiently strong to undergo the recoil of repeated firing of the handgun without damage. 
     In such embodiments, preferably but not necessarily, the proximal bar is substantially similar or identical in function and construction as described hereinabove for proximal bar  26  of butt stock  10 , the most proximal middle bar that is associated with the proximal bar is substantially similar or identical in function and construction as described hereinabove for middle bar  24  of butt stock  10 , there is a distal bar substantially similar or identical in function and construction as described hereinabove for distal bar  22  of butt stock  10 , and there are one or more additional middle bars between the distal bar and the most proximal middle bar. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. In case of conflict, the specification, including definitions, will take precedence. 
     As used herein, the terms “comprising”, “including”, “having” and grammatical variants thereof are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof. These terms encompass the terms “consisting of” and “consisting essentially of”. 
     As used herein, the indefinite articles “a” and “an” mean “at least one” or “one or more” unless the context clearly dictates otherwise. 
     As used herein, when a numerical value is preceded by the term “about”, the term “about” is intended to indicate +/−10%. 
     As used herein, a phrase in the form “A and/or B” means a selection from the group consisting of (A), (B) or (A and B). As used herein, a phrase in the form “at least one of A, B and C” means a selection from the group consisting of (A), (B), (C), (A and B), (A and C), (B and C) or (A and B and C). 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements. 
     Citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the invention. 
     Section headings are used herein to ease understanding of the specification and should not be construed as necessarily limiting.