Abstract:
A rapidly-adjustable butt stock assembly comprised of a butt stock, a buffer, a slot cylinder, a key cylinder, and keys. The butt stock has a cylindrical recess with key grooves longitudinally therein for receiving the slot and key cylinders. The key cylinder is rigidly attached to the buffer. The slot cylinder has at least one longitudinal slot with a plurality of transverse slots extending therefrom. The key cylinder carries one or more keys, which keys extend through the key cylinder and the slot cylinder and into the key grooves of the butt stock. To adjust the length of the assembly, the user rotates the slot cylinder so that the keys rotate out of the transverse slots and into the longitudinal slot of the slot cylinder thus permitting the key cylinder to move axially with respect to the butt stock.

Description:
RELATED APPLICATIONS 
     The priority benefit of U.S. provisional patent application 60/988,311, filed Nov. 15, 2007, which is incorporated herein in its entirety by reference, is claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to fire arms in general and to the butt stocks of fire arms in particular. 
     The typical butt stock is a simple, rigid component extending from the receiver of the firearm rearward and engages the user&#39;s shoulder when the firearm is in the shoulder firing position. The distance between a firearm&#39;s trigger and the rear-most portion of the butt stock is known in the art as the pull length. The pull length for a firearm, such as a rifle, having a typical, rigid butt stock is fixed. 
     A rifle having an adjustable pull length is preferable to one having a fixed pull length for a number of reasons. For example, when a rifle is used by a subsequent, different user, the subsequent user needs to be able to adjust the pull length for comfort and shooting accuracy. In addition, even if the rifle is used by a single user, the manner in which the user is using the rifle (standing versus prone) and whether the rifle is equipped with optics (e.g., a scope) or other aiming devices (e.g., a bipod) will require that the pull length be adjustable for comfort and accuracy. 
     In addition to being adjustable, it is also important for a rifle butt stock to be simple and reliable, having a small number of parts, quickly and quietly adjustable, and very rugged. This is especially true for rifles used in combat. Rifles for combat that are used in the prone position need to be especially rugged due to the fact that they are often slammed to the ground when the user is transitioning from a standing to a prone position and may then be used as support when the user is transitioning from the prone to the standing position. 
     The top portion of the butt stock, upon which the user&#39;s cheek rests when firing, is known in the art as the comb. The height of the comb of a typical, rigid butt stock is fixed. Depending on the user and manner in which the rifle is being used, a comb of a fixed height may be uncomfortable for the user or impede accurate shooting if it prevents the user from properly viewing the reticle of a sighting device. It would be advantageous, therefore, to be able to adjust the height of the comb to maximize shooting accuracy and comfort. 
     Accordingly, there remains a need for simple, reliable, and rugged butt stock that provides for quick, quiet, and easy adjustment of pull length and comb height. 
     SUMMARY OF THE INVENTION 
     According to its major aspects and briefly recited, the present invention is a rapidly-adjustable butt stock assembly. The butt stock assembly is made of a rugged, rigid material such as metal, plastic, fiberglass, or carbon fiber. It includes a buffer assembly and a butt stock with a nested slot cylinder and key cylinder carried within the butt stock. The butt stock has a generally cylindrical recess formed in it with an axis aligned with the long dimension of the firearm. One or preferably two key grooves are formed in the wall of the cylindrical hole. The slot cylinder has a longitudinal slot and several spaced-apart transverse slots; the key cylinder carries one or more keys that extend radially from the key cylinder through the slots of the slot cylinder and into the key grooves in the cylindrical recess of the butt stock. Rotating the slot cylinder so that the keys are not in the transverse slots but in the longitudinal slot allows the key cylinder to be moved axially with respect to the slot cylinder in order to increase or decrease the length of the butt stock assembly. 
     On top of the butt stock is a saddle-shaped comb, which is also made of a rugged, rigid material. The front portion of the comb is pivotally attached to the butt stock so that the rear portion can be elevated above the butt stock by pivoting it with respect to the front portion. The opposing rear portion of the comb has two holes on each side that are dimensioned to receive a pair of spring-loaded buttons extending from the sides of the butt stock. The buttons can be pressed to free the comb from a first pair of comb holes. The comb can then be elevated until the next pair of comb holes comes into registration with the spring-loaded buttons. Releasing the buttons allows them to extend though these holes and thus secures the comb at the different elevation. 
     Residing within the cylindrical hole in the butt stock and extending from front to rear is a mechanism that allows the pull length of the firearm to be changed. This mechanism is comprised of a slot cylinder, a key cylinder within the slot cylinder, and keys carried by the key cylinder. The front end of the slot cylinder is open to receive the key cylinder; its back end is closed. The slot cylinder is free to rotate about its longitudinal axis within the cylindrical hole of the butt stock. The slot cylinder has at least one longitudinal slot and a plurality of spaced-apart transverse slots extending from the longitudinal slot so that the transverse slots communicate with each other and with the longitudinal slot. The slot cylinder remains almost entirely within the butt stock, but it has a collar at its front end that is exposed for use in rotating the slot cylinder. To rotate the slot cylinder, the user grips and rotates the collar, thereby rotating the slot cylinder within the butt stock. 
     Inside the slot cylinder and free to slide longitudinally therein is the key cylinder with two keys extending radially from the key cylinder. The length of each key is greater than the thickness of the slot cylinder&#39;s wall. Accordingly, the key of the key cylinder can extend through the slots of the slot cylinder and into the key groove of the cylindrical hole of the butt stock so as to prevent rotation of the key cylinder. However, the key cylinder can still move axially with respect to the butt stock. The key cylinder is attached to the receiver of the firearm through a buffer assembly. 
     When the key of the key cylinder extends through the transverse slots of the slot cylinder, butt stock assembly is in the “locked” position and the key cylinder cannot move axially with respect to the slot cylinder. But, when the key of the key cylinder extends through the longitudinal slot of the slot cylinder, the butt stock assembly is in the “unlocked” position and the key cylinder is then free to move axially with respect to the butt stock. A torsion spring within the butt stock urges the slot cylinder to rotate so that the key returns in the transverse slot, in the “locked” position, when the user is not manually rotating the collar. 
     To adjust the length of the butt stock assembly, the user, holding the rifle in one hand and the collar in the other, rotates the collar thereby rotating the slot cylinder against the urging of the torsion spring so that the key is moved out of the transverse slot and into the longitudinal slot. The key cylinder can then be moved axially with respect to the butt stock. By that axial movement, the user adjusts the pull length. When the user has adjusted the butt stock assembly to the desired pull length, the user then allows the torsion spring to rotate the slot cylinder back so that the key is recaptured within the transverse slots. The key cylinder is then, once again, in the “locked” position and can no longer be moved axially with respect to the butt stock. The user can then aim and fire the rifle in the same manner as before the pull length was adjusted. 
     These and other features and their advantages will be apparent to those skilled in the art of firearm technology from a careful reading of the Detailed Description of Preferred Embodiments accompanied by the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is a side view of a firearm showing the adjustable butt stock assembly with its shortest pull length, according to a preferred embodiment of the present invention; 
         FIG. 2  is a partial side view of the firearm of  FIG. 1  showing the adjustable butt stock assembly with its longest pull length, according to a preferred embodiment of the present invention; 
         FIGS. 3A-3D  are a series of perspective, exploded views of the butt stock, slot cylinder and key cylinder showing the transition from a locked butt stock assembly, an unlocked butt stock assembly, an axially adjusted pull length, and back to a locked butt stock assembly, according to a preferred embodiment of the present invention; 
         FIG. 4  is side cross-sectional view of the present butt stock assembly with pull length at its shortest, according to a preferred embodiment of the present invention; 
         FIG. 5  is side cross-sectional view corresponding to that of  FIG. 4  with pull length at its longest, according to a preferred embodiment of the present invention; 
         FIG. 6  is an exploded front end view of the butt stock, according to a preferred embodiment of the present invention; 
         FIG. 7  is a rear view of the butt stock without a cover plate, according to a preferred embodiment of the present invention; 
         FIG. 8  is a perspective view of the cover plate showing the spring-loaded button mechanism, according to a preferred embodiment of the present invention; 
         FIG. 9  is a side view of the butt stock with cover plate shown being removed from the butt stock, according to a preferred embodiment of the present invention; and 
         FIG. 10  is a side view of the butt stock showing the comb elevated to a higher position, according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a rapidly-adjustable butt stock assembly for use on a fire arm. For convenience, the muzzle end of the firearm is the fore end or front end and the cover plate end of the firearm is the back end or rear end. The firearm illustrated in  FIG. 1 , and generally indicated by reference number  10 , has a major dimension, running from front to back, or muzzle end to cover plate end, which will define an axis. Unless otherwise defined herein, reference to axes is a reference to axes parallel to this major dimension. Rotations are with respect to this axis or an axis parallel to this one; axial movement means movement along this axis or an axis parallel to this one. 
     Referring now to  FIGS. 1 and 2 , there is illustrated firearm  10  with a receiver  12 , a barrel  14  on the end of receiver  12  and a muzzle  16  on the end of barrel. A bipod  18  may be used to support barrel  14 . A trigger assembly  20  may be used to operate receiver  12 . A front sight  22  cooperates with rear sight  24  to allow the user to aim firearm  10  so that when ammunition is fed into receiver  12  at opening  26  and a trigger  28  is pulled, the firearm will fire bullets (not shown) through barrel  14  and muzzle  16 . 
     Rearward of receiver  12  is a butt stock assembly  40  according to a preferred embodiment of the present invention. Butt stock assembly  40  has a saddle-shaped comb  42  carried on a butt stock  44 . Butt stock  44  has a front portion  46  and an opposing rear portion  48 . Comb  42  has a front portion  50  that is carried by a pivot pin  52  proximate to front portion  46  of butt stock  44  so that a rear portion  54  of comb  42  can be raised to elevate its position when desired by the user, as will be described in more detail herein. Butt stock  44  carries a cover plate  56  on rear portion  48 . 
     The pull length of firearm  10  is defined as the distance from trigger  28  to cover plate  56 .  FIG. 1  shows butt stock assembly  40  in a configuration wherein its pull length is shortest;  FIG. 2  shows butt stock assembly  40  in a configuration wherein its pull length is longest. Butt stock assembly is joined to receiver using a buffer assembly  60 . 
       FIGS. 3A-3D  are a series of views of several components of butt stock assembly  40  that permit the pull length of firearm  10  to be increased or decreased. In order that butt stock assembly  40  remains stable when its pull length has been set, it will lock into position automatically. To change its pull length, it must be unlocked. Accordingly,  FIG. 3A  illustrates the relevant components, in an exploded view, in an initial, locked configuration with a first pull length;  FIG. 3B  illustrates these components in the unlocked position but at the same pull length;  FIG. 3C  shows the same components with the pull length increased but still in the unlocked position; and finally, in  FIG. 3D , in the longer pull length, but with the components again in the locked position. 
     Taking each of these four figures in order beginning with  FIG. 3A , there is shown a butt stock  70  having a generally cylindrical recess  72  formed therein that is open toward the front. Formed toward the top and toward the bottom of cylindrical recess  72  are two, opposing key grooves  74 . A nested pair of cylinders is shown that are normally inserted into cylindrical recess  72 , but are shown in  FIG. 3A  removed for ease of understanding. The outer cylinder is a slot cylinder  76  with a longitudinal slot  80  and plural, spaced-apart transverse slots  82 . Transverse slots  82  communicate with longitudinal slot  80 . A second set of transverse and longitudinal slots is on the opposing side of slot cylinder and not visible in  FIGS. 3A-3D . 
     Inside slot cylinder  76  is a key cylinder  86  carrying two keys  90 ,  92 . Key cylinder  86  is attached to buffer assembly  88 . Keys  90 ,  92  are fixed in key cylinder  86  and extend radially outward from key cylinder  86 , on opposing sides, through the thickness of slot cylinder  76  and an additional distance sufficient to fit into key grooves  74  of butt stock  70 . In order for key cylinder  86  and slot cylinder  76  to be inserted into butt stock  70 , keys  90 ,  92 , must be oriented so that they will fit into key grooves  74 . Once key cylinder  86  is inserted into cylindrical recess  72 , keys  90 ,  92  prevent key cylinder  86  from being rotated about its own axis; however, it can still be moved axially. Slot cylinder  76 , however, once inserted into cylindrical recess  72  and held in an axial location by inserting a pin  150  (best seen in  FIG. 6 ) through recess  94  and into a groove  156  located on the outside diameter of slot cylinder  76 , will be prevented from axial movement but will still have radial movement when keys  90 ,  92  are in transverse slots  82 . It is the limited radial movement of slot cylinder  76  and axial movement of key cylinder  86  that permit the locking, unlocking and extending of butt stock assembly  40 . 
     In  FIG. 3A , keys  90 ,  92 , are in transverse slots  82  thus preventing axial movement of key cylinder  86 . Under these circumstances, butt stock  70  is in a locked position, meaning that its pull length will not change. Rotation of slot cylinder  76  in the counter-clockwise direction (looking toward muzzle  16 ) as shown by the arrow in FIG.  3 B by grasping a collar  98  on the forward end of slot cylinder  76  and rotating places keys  90 ,  92  in longitudinal slot  80 , to permit the axial movement of key cylinder  86 . As slot cylinder  76  is rotated, a cylinder tab  100  on its back end increasingly loads a torsion spring  102  (see arrow). Butt stock  70  is thus placed in an unlocked position in which its pull length can be changed as long as collar  98  is held against the urging of torsion spring  102 . Comparing the axial position of key cylinder  86  with respect to slot cylinder  76  in  FIGS. 3C to 3B  shows that key cylinder  86  has moved axially with respect to slot cylinder  76  as indicated by the arrow in  FIG. 3C . 
     Next, slot cylinder  76  is allowed to rotate clockwise when collar  98  is released, thus enabling cylinder tab  100  to reduce torsion spring  102  (see arrow). Slot cylinder  76  is rotated in the direction of the arrow in  FIG. 3D  to place keys  90 ,  92 , in transverse slots  82  rather than longitudinal slot  80 , placing it in a locked position held in position radially by the torsion spring  102 , and thus preventing butt stock  70 &#39;s axial movement once again. The force that rotates slot cylinder  76  is provided by the force of torsion spring  102  against slot cylinder tab  100  extending through slot  194  (see  FIGS. 6 and 7 ). 
       FIGS. 4 and 5  show side, cross-sectional views of butt stock assembly  110  in the minimum pull length and maximum pull length positions. It will be clear that intermediate positions are possible and, indeed, four positions are possible with the design shown. Assembly  110  includes a buffer assembly  112  running through much of assembly  110 , beginning, from left to right, coupler  114 , buffer piston  116  and buffer spring  120  all housed within buffer housing  122 . Coupler  114  allows butt stock assembly to be coupled to the receiver of the firearm. Buffer piston  116  and buffer spring  120  take up the recoil of each round fired. 
     Buffer housing  122  is a cylinder that is fitted within key cylinder  128  which in turn carries two keys  130 ,  132 . Keys  130 ,  132 , may extend radially in both directions from key cylinder  128 , through slots formed in a slot cylinder  136 . In  FIGS. 4 and 5  only transverse slots  138  are visible and there are six of them in this embodiment. 
     A collar  140  is integrally attached to the fore end of slot cylinder  136  to allow the user to rotate slot cylinder  136  with respect to key cylinder  128  from the locked position, as shown in  FIGS. 4 and 5 , to the unlocked position wherein a longitudinal slot (see  FIGS. 3A-3D ) is aligned with keys  130 ,  132 . 
     Slot and key cylinders  136 ,  128 , fit within cylindrical recess of butt stock  142 , with keys  130 ,  132 , extending into key grooves  144 ,  146 , respectively, to prevent rotation of key cylinder  128 . A U-shaped pin  150 , best seen in  FIG. 6 , is inserted into U-shaped hole  190  formed in the side of butt stock  142  and thence into an annular groove  156  formed in slot cylinder  136 , with the ends of pin  150  being transverse to slot cylinder  136 , as best seen in  FIGS. 3A-3D . Groove  156  is formed in the back end of slot cylinder  136  to receive pin  150  which thus prevents slot cylinder  136  from moving axially when key cylinder  128  is moved axially. Butt stock  142  has a compression spring  148  to urge key cylinder  128  forward when keys  130 ,  132 , are in the longitudinal slot of slot cylinder  136 . One end of compression spring is seated on a bushing  152  at the back end of butt stock  142  and the opposing end of compression spring  148  is seated on a similar bushing  154  on the back end of key cylinder  128 . Compression spring  148  is compressed when key cylinder  128  is moved to the shortest pull length, as shown in  FIG. 4 , and is relieved when moved to its longest pull length, as shown in  FIG. 5 . 
     Butt stock  142  includes a cover plate  160  having a hook  162  at the top and a spring-loaded button mechanism  164  at the bottom to secure cover plate  160  to butt stock  142 . Hook  162  is inserted into a cutout  170  at the top of butt stock  142  and opposing spring-loaded buttons  172  of spring-loaded button mechanism extend through opposing holes formed in the sides of butt stock  142  (as best seen in  FIGS. 9-10 ) to secure cover plate  160  to butt stock  142 . A saddle-shaped comb  180  is carried on top butt stock  142 . 
     A torsion spring  180  is carried on a bushing  182  at the rearmost portion of butt stock  142  to urge slot cylinder  136  to rotate to the locked position. The end  184  of torsion spring  102  extends downward and catches cylinder tab  100  so that when slot cylinder  136  is rotated, cylinder tab  100  tightens torsion spring  102 . When collar  140  is used to rotate slot cylinder  136  counter-clockwise, slot cylinder  136  is moved against the urging of torsion spring  102 . Releasing collar  140  causes torsion spring  102  to rotate cylinder tab  100  and, with it, slot cylinder  136  counter-clockwise to the locked position. 
       FIG. 6  illustrates an exploded, front view of butt stock  142  with U-shaped pin  150  to the left. Pin  150  fits into a U-shaped hole  190  and into an annular groove  156  on slot cylinder  136  (see  FIGS. 3A-3D  for annular groove  156 ) to capture slot cylinder  136  and thereby prevent its axial movement when key cylinder  128  is moved axially. A crescent-shaped hole  194  in the back of butt stock  142  permits cylinder tab  100  of slot cylinder  136  to extend rearward beyond the back of butt stock to capture end  184  of torsion spring  102  and, load torsion spring  102  when slot cylinder  136  is rotated counter-clockwise. Finally, at the top of butt stock  142  are two pivot pins  198  about which the front portion of comb will pivot. 
       FIG. 7  illustrates the back view of butt stock  142 . Visible in  FIG. 7  is a bushing  182  for torsion spring  102  and crescent-shaped hole  194  for the tooth-shaped end portion of slot cylinder  136  and pivot pins  198  for the comb. Below, two ribs  200  help to reinforce butt stock  142  and align spring-loaded button mechanism  164  of cover plate  160 . 
       FIG. 8  is a perspective view of cover plate  160  showing spring-loaded button mechanism  164  and hook  162 . Button mechanism  164  includes two spring-loaded buttons  210 . with a spring  212  urging them laterally in opposing directions. Small transverse pins  214  hold buttons  210  to cover plate  160 . 
       FIG. 9  shows a side view of butt stock  142  with cover plate  160  shown rotated away from butt stock  142 , as indicated by the arrow. Cutout  170 , shown at the top rear of butt stock  142 , is dimensioned to receive hook  162  and thereby hold the top of cover plate  160  to butt stock  142 . Spring-loaded button mechanism  164 , when buttons  210  are both pressed, will slide into the lower portion of butt stock  142  and, when fully seated, buttons  210  will extend through holes  216  of butt stock  142  to hold the lower portion of cover plate  160  to butt stock  142 . Also visible in  FIG. 9  is pivot pin  198  for the comb and U-shaped pin  150  in U-shaped hole  190 . Hole  190  has an enlarged portion  218  to facilitate removal of pin  150  and release of slot cylinder  136  for cleaning the interior of butt stock  142 . 
       FIG. 10  illustrates butt stock  142  with comb  180  in an elevated position compared to that shown in  FIG. 2 . The front portion  222  of comb  180  pivots about pivot pin  198  to allow rear portion  224  to be raised or lowered to different elevations. Holes  226 ,  228  allow two different elevations of comb  180  to be secured when button  210  extends through hole  226  or  228  depending on the elevation of rear portion  224  of comb  180 . Partially pressing button  210 , allows the elevation of rear portion  224  of comb  180  to be changed; completely pressing button  210 , allows cover plate  160  to be removed from butt stock  142 . Thus, spring-loaded button mechanism serves two purposes: allowing height adjustment of the rear portion  224  of comb  180  and securing or releasing cover plate  160 . 
     It is intended that the scope of the present invention include all modifications that incorporate its principal design features, and that the scope and limitations of the present invention are to be determined by the scope of the appended claims and their equivalents. It also should be understood, therefore, that the inventive concepts herein described are interchangeable and/or they can be used together in still other permutations of the present invention, and that other modifications and substitutions will be apparent to those skilled in the art from the foregoing description of the preferred embodiments without departing from the spirit or scope of the present invention.