Abstract:
A bipod for a light-weight machine gun is disclosed. The bipod has tubular telescoping legs with large ground-engaging feet that may be extended and retracted to discreet locking positions. The bipod has a spring-based system that allows a user to pivot the bipod legs about cylinder-in-a-cylinder pivot pins, either towards or away from the barrel muzzle with one hand, thus giving 180 degrees of travel. The bipod is attachable to a machine gun with a round yoke using a stepped screw and compression spring that assures yoke remains tightly secured to body, but rotatable for traversing, during extended use.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The priority benefit of U.S. provisional patent application 61/107,555, filed Oct. 22, 2008, which is incorporated herein in its entirety by reference, is claimed. This application is related to U.S. Pat. No. 6,763,627 issued to the present applicant Jul. 20, 2004, and which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to firearms, and specifically to bipods for use with a light-weight machine gun. A machine gun is not a shoulder-fired weapon like a rifle. It may be fired from the hip but is best fired when supported at the muzzle end by a bipod or other structure. Machine guns are heavy, they become quite hot when fired, and the forces associated with rapid firing makes it difficult to maintain accurate targeting unless the muzzle end is properly supported. 
     A bipod has been a staple accessory for many military firearms since the beginning of firearm development. The bipod generally cradles the barrel of a firearm and has two legs that can be planted on the ground. The bipod provides stability and support for the weapon when fired, especially when fired in long bursts. 
     To be effective, a machine gun must be highly mobile and rapidly deployable. The light-weight machine gun with its bipod must be capable of being removed from one position, carried in a variety of transportation vehicles (e.g. personnel carriers, airplanes, open trucks, etc) to another position, and set up quickly, and the attached bipod should not interfere with that redeployment. A bipod must also meet other common military objectives such as low weight, ease of use, simple construction, low cost, and high durability. 
     The twentieth century advent of the light-weight machine gun and the mechanized military has led to a refinement in the state of the art of bipods. Far from just a simple inverted V, current bipods are more complicated devices that include telescoping legs, swivel mounts, and folding structures. For example, U.S. Pat. No. 4,351,224, issued to Curtis, teaches a pair of L-shaped channels that telescope and fold from a deployed position to a stowed position. This bipod only allows for one direction of leg travel and each leg must be folded individually. U.S. Pat. No. 4,625,620, issued to Harris, teaches a pair of telescoping tubular legs that are individually folded and adjusted. In U.S. Pat. No. 5,711,103, issued to Keng, a swivel mount is incorporated into a bipod that allows a gunner to aim the weapon while keeping the bipod stationary. Keng also teaches a pair of telescoping tubular legs that are frictionally locked. 
     The prior art of firearm bipods, while extensive, is not without shortcomings. Many of the designs have many parts. One significant drawback to the prior art is that the bipod legs must be deployed separately, i.e. the legs must be unfolded one at a time rather than with a single motion. This means the user must either make two separate motions, or must set the gun down and unfold the legs with both hands. The releasing mechanisms that allow the legs to telescope and fold, such as the one disclosed by Curtis, are often overly complex, unreliable, or create a device that is somewhat unwieldy when transported in a small vehicle. Many of the designs, such as the one employing tubular legs with frictional locks as disclosed by Keng, are not suitable for military applications because they are not suitable for combat; dirt or damage to the legs can interfere with the telescoping. 
     The bipod disclosed in related patent, U.S. Pat. No. 6,763,627, issued to Kaempe, while a significant improvement over the prior art, also suffers in the rugged environment of use. Certain parts loosen or break, such as the e-clip, or become clogged with dirt or sand making the deployment of the legs of the bipod difficult. Therefore, there remains a need for an improved bipod that will be more robust, and easier and quicker to use than prior art bipods. 
     SUMMARY OF THE INVENTION 
     Briefly recited and according to its major aspects, the present invention is a bipod for a firearm such as a light-weight machine gun in which the telescoping legs can be deployed with one hand. The present invention has two legs that are connected by spring-based system that allows the legs to be deployed from a stowed position by applying pressure to just one leg. The legs of the present bipod may be stored facing either towards the stock of the gun or towards the muzzle. Improved pivot pins made with a cylinder within a cylinder facilitate repeated pivoting the legs between a parallel orientation, such as when in the stored position, and a splayed orientation such as when in the deployed position. 
     When the legs are folded from the stored position to the deployed position, the spring-based system acts on the legs, causing them to deploy. The spring-based system is housed inside a body that supports a yoke cradling the barrel of the gun in such a way that the gun and its yoke can be rotated radially through a small angle with respect to the body allowing the barrel of the machine gun to traverse left and right without moving the deployed bipod legs. The yoke is held securely to the body so that despite extended and rough handling, the yoke remains freely rotatable. 
     Each leg can telescope incrementally between a minimum length and a maximum length, using spring-loaded buttons to lock the legs in place once the desired length is reached. However, because of the design of the buttons, the user can extend the legs simply by pulling on the end of the leg. The foot of each leg is large enough to provide firm footing on a variety of surfaces including softer surfaces such as mud and sand. 
     An important feature of the present invention is the improved security of the attachment of the yoke to the body. The use of a stepped screw with compression spring assures a firm hold between the two. 
     Another important feature is the larger feet of the telescoping legs. The larger feet are more than an inch and one half in diameter as opposed to less than an inch for better stability on softer ground. 
     Still another feature of the present invention is the use of pivot pins each comprising a pin assembly formed by placing a cylinder within a cylinder to allow the two legs to pivot with respect to the body. The pin assembly consists of an inner coiled cylinder captured by an outer slotted cylinder. The inner cylinder exerts and distributes spring pressure uniformly absorbing shock and vibration outwards against the slotted cylinder to increase strength and detention. 
     Other features and their advantages will be apparent to those skilled in the art of firearm accessory design and fabrication from a careful reading of the Detailed Description of Preferred Embodiments accompanied by the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is an exploded perspective view of the bipod in the deployed position 
         FIG. 2  is a perspective view of the assembled bipod in the deployed position; 
         FIG. 3A  is a top perspective view of the bipod in the stowed position and fully retracted; 
         FIG. 3B  is a perspective view of the bipod in a deployed position with the legs retracted and showing the direction in which the legs are urged by the spring-based system; 
         FIG. 4  is a perspective view of the bipod in an alternate stowed position with legs fully retracted; 
         FIG. 5  is a detailed, perspective, top view of the bipod yoke; 
         FIG. 5A  is a detailed perspective of pin  88 ; 
         FIG. 6  is a detailed perspective bottom view of the bipod yoke; 
         FIG. 7  is a cross-sectional view taken along lines  7 - 7  of  FIG. 2 ; and 
         FIG. 8  is a cross-sectional view taken along lines  8 - 8  of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention is a bipod with telescoping legs that can be deployed with one hand. 
     Referring now to  FIGS. 1 and 2 , there are shown perspective exploded and assembled views of a preferred embodiment of the present invention, namely, a bipod for a light-weight machine gun generally indicated by reference number  10 . Bipod  10  has two legs  12  and  14  that are attached to a body  16 . Body  16  supports a yoke  18  that is dimensioned for encircling the barrel of a firearm such as a machine gun. 
     Bipod  10  is shown in the deployed configuration in  FIGS. 1 and 2 , with legs  12  and  14  splayed to provide stability. Each leg  12 ,  14 , has a foot  22 ,  24 , respectively, that engages the ground or other surface and is preferably formed to resist lateral movement. For secure footing, feet  22 ,  24 , are large and have teeth  26 ,  28 , respectively, to bite into a surface such as the ground or a sandbag, for example, and resist lateral movement. Feet are large to be useful on soft ground such as sand or mud, preferably, having at least approximately eleven square centimeters of ground-engaging area. 
     Legs  12  and  14  are telescoping. Here, internal rods  34 ,  36 , in tubes  38  and  40  provide this telescoping capability (only one rod, rod  34 , is shown in  FIGS. 1 and 2 , but a second rod, rod  36  in tube  40 , is identical to rod  34  in tube  38  and can be seen in cross section in  FIG. 6 ) as tube  38  can receive rod  34  in its interior or be pulled axially with respect to rod  34  to lengthen leg  12 . In particular rods  34 ,  36 , have an outer diameter that is smaller than the inner diameter of tube  38  and tube  40  so that rods  34 ,  36 , can slide axially in and out of tubes  38 ,  40 . To secure rods  34 ,  36 , with respect to tubes  38  and  40  at various relative positions, rods  34 ,  36  have spring-loaded, pivoting buttons  44 ,  46 , and tubes  38  and  40  have a series of holes  48 ,  50 , dimensioned to receive buttons  44 ,  46 . 
     Buttons  44 ,  46  will extend through holes  48 ,  50 , when in rods  34 ,  36 , bring buttons  44 ,  46 , in registration with holes  48 ,  50 , and of tubes  38 ,  40 , and, by doing so, prevent telescopic collapse of legs  12 ,  14 . However, because buttons  44 ,  46 , are spring-loaded and curved, they permit telescopic extension of legs  12 ,  14 , merely by pulling on feet  22 ,  24 . In particular, buttons  44 ,  46 , are oriented to have a major dimension parallel to the long axis of rods  34 ,  36 . Each button  44 ,  46 , has a first end  60  toward body  16  and a second end  62  oriented toward feet  22 ,  24  (only one button, button  44 , is shown exploded in  FIG. 1  but button  46  is identical to button  44 ). Second end  62  is urged outward or away from the axis of rod  34  by a spring  66 . First end  60  of button  44  is free to pivot about a pin  70  oriented so that button  44  pivots about an axis perpendicular to the long dimension of rod  34 . The surface of buttons  44 ,  46  is curved so that, when feet  22 ,  24  are pulled, buttons  44 ,  46  are crammed inward, toward rods  34 ,  36 , but when feet  22 ,  24 , are pushed toward body  16 , buttons  44 ,  46 , will catch on tubes  38 ,  40  at holes  48 ,  50 , and cannot be pushed further unless pressed inward against rods  34 ,  36 , held while feet  22 ,  24  are pushed sufficiently so that buttons  44 ,  46  go out of registration of holes  48 ,  50 . The maximum and minimum extent of telescoping of rods  34 ,  36 , respect to tubes  38 ,  40 , is limited by stop pins  68  in slots  76  ( FIGS. 3A ,  3 B, and  4 ). When stop pin  68  reaches the ends of slot  76 , rods  34 ,  36 , either completely telescopingly extended with respect to tubes  38 ,  40 , or completely telescopingly retracted. 
     Referring to  FIGS. 1 ,  2 ,  5 - 8 , bipod  10  is attached to a firearm barrel by yoke  18 , which is ring-shaped and strong enough to provide durable support for a machine gun barrel during extended operation, and preferably made of metal or metal alloy. Yoke  18  is attached to a body  16  by a stepped screw  52  inserted into a threaded hole  54  in yoke  18  through a hole  56  in body  16 . A compression spring  58  is held between body  16  and screw  52  by placing spring  58  over screw  52  and attaching it to yoke  18  through hole  56  in body  16  and then screwing it into threaded hole  54  on yoke  18 . See  FIGS. 1 and 2 . Screw  52  is further retained to threads  54  in yoke  18  by applying a thread locking compound. The addition of spring  58  maintains a flexible but pre-loaded interface that will allow yoke  18  to rotate in relation to body  16  but prevent wobble or vibration. It also provides a spring force to cause yoke  18  to return to its nominal position in a recess  106  formed on body (as best seen in  FIG. 1 ) which helps to hold bipod  10  in line with the barrel of the gun when legs  12 ,  14  are folded. This rotation allows a gunner to pivot the barrel of the gun through a small angle in a plane lying perpendicular to a line bisecting the splayed legs  12 ,  14 , so that the gun carried by yoke  18  has a field of fire without moving legs  12 ,  14 . The pivot angle is defined by ledges  64  on body  16  ( FIG. 5 ) that limit the rotation of yoke  18  within hole  56  of body  16 . 
     Referring in particular to  FIGS. 1 and 7 , in the preferred embodiment, body  16  is essentially a hollow cylinder open at both ends and having cutout portions  72 ,  74  for receiving the tops  78 ,  80 , of legs  12 ,  14 , respectively, when legs  12 ,  14 , are splayed. Legs  12 ,  14 , are held securely to body  16  by a tie member  82  that is received within body  16  but which extends far enough beyond the ends of body  16  to allow it to be inserted into slots  84 ,  86 , formed in tops  78 ,  80 , of legs  12 ,  14 , where it is secured with pins  88 ,  90 . 
     Pins  88 ,  90 , may each be formed of a first cylinder  110  within a second cylinder  112 , as best seen in  FIG. 5A . First cylinder  110  is comprised of a coiled pin captured by outer slotted second cylinder  112  so that pins  88 ,  90  have the detention and strength required when in the holes formed in tie member  82  of legs  12 ,  14 , that receive them. Thus, both first and second cylinders  110 ,  112 , may act as springs and thereby provide smooth operation without wobble when legs  12 ,  14  are being deployed or stored, yet may avoid the need for a tight-tolerance that may become a problem in a difficult environment of use. 
     Inside body  16  is a compression spring  92  that encircles tie member  82  and is flanked by two plungers  94  (see  FIG. 1  and  FIG. 7 ) each of which is a hollow cylinder and has a cutout portion  96  for receiving tops  78 ,  80 . Compression spring  92  resists the movement of plungers  94  toward each other and urges plungers  94  axially outward of body  16 . Each plunger  94  is retained inside body  16  by pins  120 ,  121 , which also limit each plunger  94 &#39;s motion axially and rotationally through engagement with cuts  122 ,  123 , formed in the bottom of each plunger  94 . Cutout portion  96  is alignable with cutout portion  72  so that, when they are aligned, tops  78 ,  80 , will be received in both of them as legs  12 ,  14 , are rotated to a splayed position. When legs  12 ,  14 , are splayed, feet  22 ,  24 , rotate outwardly and tops  78 ,  80 , rotate into cutout portions  72  and  96 . The plungers  94  are prevented from rotating by the engagement of pins  120 ,  121 , within cuts  122 ,  123 . 
     Meanwhile plungers  94 , urged by compression spring  92 , in turn urge legs  12 ,  14 , to the splayed, deployed position whenever legs  12 ,  14 , are rotated from either of two stored positions. Plungers  94  accomplish this by the engagement of their leading edges  102  against legs  12 ,  14 , at points just below where pins  88 ,  90 , connect tie member  82  to legs  12 ,  14 . By applying pressure at that point, leading edges  102  of plungers  94  cause legs  12 ,  14 , to pivot about pins  88 ,  90 , to move tops  78 ,  80 , into cutout portions  72 ,  96 , but only when legs  12 ,  14 , have been rotated to the point where tops  78 ,  80  are able to be received within the aligned cutout portions  72 ,  74 , i.e., to the position where they are to be deployed. 
     When legs  12 ,  14 , have been rotated to either stowed position, tops  78 ,  80 , will not be aligned for receipt into cutout portions  72 ,  96 , and no rotation of legs  12 ,  14 , can take place. In fact, when bipod  10  is in either stored position, leading edge  102  of plunger  94  will be engaging legs  12 ,  14 , both above and below pins  88 ,  90  so no rotation will take place. Preferably, leading edge  102  of each plunger  94  has a pair of concave curves  104  formed on it (best seen in  FIGS. 5 ,  6 , and  7 ) so that legs  12 ,  14 , are preferentially urged into the two stored positions (which will be described in more detail below). 
       FIGS. 3A ,  3 B, and  4  illustrate the three positions of bipod  10 .  FIG. 3A  shows bipod in a stored position with the axis of yoke  18  parallel to the axes of legs  12 ,  14 . When mounted onto the barrel of a machine gun or other gun in the configuration shown in  FIG. 3A  with barrel pointed to the right, legs  12 ,  14 , extend rearward relative to the muzzle end of the barrel and aligned parallel to the barrel. 
       FIG. 3B  illustrates bipod  10  with legs  12 ,  14  oriented with respect to yoke  18  so that legs  12 ,  14  will spring into the deployed position in which they are splayed, as indicated by the arrows in  FIG. 3B , and perpendicular to that of their stored position, as shown in  FIG. 5 . 
       FIG. 4  illustrates bipod  10  with yoke  18  oriented in the second of two stored positions. When bipod  10  is mounted to the barrel of a gun so that the barrel is pointed to the left, legs  12 ,  14 , will extend away from but again parallel to the barrel. The machine gun is able to fire when legs  12 ,  14 , are in any of these three orientations. 
     In use, bipod  10  is mounted to a machine gun and, if not already in one of the two stored positions, is placed in either stored positions by first pushing legs  12 ,  14 , together so that they are parallel. Then legs  12 ,  14 , can be rotated while held in parallel to either the position shown in  FIG. 3A  or  4  from that shown in  FIG. 3B . 
     To deploy bipod  10 , either leg  12 ,  14 , can be grasped and rotated 90° toward the ground from either stored position. As leg  12  or  14  reaches the 90° point, compression spring  92  will force plungers  94  laterally and push legs  12 ,  14 , outward at feet  22 ,  24 . The user can then grasp either foot  22 ,  24 , of legs,  12 ,  14 , and pull to extend the length of that leg. At intervals along the length of legs  12 ,  14  as they are being telescopingly extended, buttons  44 ,  46 , on rods  34 ,  36 , will come into registration with holes  48 ,  50  in tubes  38 ,  40 , so that they will extend through holes  48 ,  50 . If feet  22 ,  24 , are pulled farther, buttons  44 ,  46 , will be crammed into rods  34 ,  36 , by tubes  38 ,  40 , to allow additional length, until the desired lengths for legs  12 ,  14 , are reached and buttons  44 ,  46 , have again come into registration with another set of holes  48 ,  50 . 
     Once bipod  10  is in the deployed position, the machine gun on which it is mounted can be placed in position and the gunner can check his or her field of fire by rotating yoke  18  through the angle permitted by ledges  64  on body  16 . He can also rotate the machine gun axially through the angle permitted by ledges  110  on yoke  18 . 
     It will be readily apparent to those skilled in the art of firearm accessory design and fabrication that many changes and substitutions can be made to the foregoing preferred embodiments without departing from the spirit and scope of the present invention, defined by the appended claims.