Abstract:
An insert assembly for a weapon is disclosed. The weapon may be a rifle, such as an M4 carbine. The insert assembly is configured to support a bolt while the bolt moves during recharging and firing cycles. The insert may be configured to continuously press on an upper receiver when the rifle is assembled. These features improve shooting accuracy of the rifle by minimizing and/or making consistent movements of the rifle&#39;s internal components (i.e., there is less wobbling of the components with respect to each other). The insert assembly may include a support plate and a hollow protrusion rigidly attached to the plate. A piston and a spring are inserted into the protrusion. The piston slides within the protrusion and is pushed against the bolt of the rifle by the spring.

Description:
FIELD OF THE INVENTION 
       [0001]    This application relates generally to firearms and more specifically to an insert for a small arm, typically a rifle, which provides greater accuracy for the weapon. 
       BACKGROUND 
       [0002]    Many firearms, such as the assault rifles commonly used in military and law enforcement situations, are designed by their manufacturers to have a bolt assembly driven in a reciprocal motion between two positions. One example includes the AR-15 family of firearms, which in turn includes the M16-type firearms. The M16-type firearms are military versions and are capable of operating in a fully automatic mode. As originally designed, the AR-15, M16, and M4 firearms are collectively and generically referred to as “M16-type” firearms or rifles. An M16-type rifle includes auto loading features and is capable of operating in a semi-automatic regime, a full-automatic regime, a burst-fire regime, a selective-fire regime, or various combinations of the above. As such, the M16-type rifle is used for a higher volume of firing than many other types of firearms and accordingly may be susceptible to higher levels of heat, fouling, and component failures. 
       SUMMARY OF THE INVENTION 
       [0003]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0004]    Provided is an insert assembly for installing into small arm, typically a rifle such as an M4 carbine. The insert assembly is received in a lower receiver of the rifle. The insert assembly is configured to support a bolt while the bolt moves during firing and reloading cycles. In some exemplary embodiments, the insert is configured to continuously press on an upper receiver when the rifle is assembled. These features tend to improve shooting accuracy of the rifle by minimizing and/or making consistent some undesirable movements of the rifle&#39;s internal components (i.e., there is less wobbling of the components with respect to each other). In some exemplary embodiments, the insert assembly includes a support plate and a hollow protrusion rigidly attached to the plate. A piston and a spring are inserted into the protrusion. The piston slides within the protrusion and is pushed against the bolt of the rifle by the spring. 
         [0005]    In some exemplary embodiments, an insert assembly for a rifle includes a support plate configured for insertion into a lower receiver of the rifle, a hollow protrusion rigidly attached to the support plate, a piston inserted into the hollow protrusion, and a spring inserted into the hollow protrusion between the piston and the support plate. A combination of the support plate and the hollow protrusion is sometimes referred to as a body. The piston is sometimes referred to as a “nub pilot” or as a “nubbin.” The support plate has a front surface that contacts the protrusion and a spring. The protrusion, in fact, extends away from the front face of the support plate. The piston is configured to slide inside the hollow protrusion in a direction substantially perpendicular to the front surface. The piston includes a top surface for supporting a bolt of the rifle while the bolt slides over the top surface in a direction substantially parallel to the top surface. The spring is configured to exert a predetermined force on the piston, thereby pushing the piston against the bolt and away from the front surface. In some exemplary embodiments, the top surface of the piston is substantially parallel to the front face of the support plate. 
         [0006]    The top surface of the piston may include a chamfer. The chamfer may be used to allow uneven portions of the bolt to slide over the top surface. The chamfer may be also used to locate the bolt keyway when the bolt moves reciprocally between its two working positions during firing and reloading. In certain embodiments, the hollow structure and piston include one or more aligning features for controlling orientation of the chamfer with respect to the support plate and/or the protrusion. 
         [0007]    The top surface of the piston may be made of wear resistant stainless steel, such as 17-4 Stainless 43/45 RC. The support plate and protrusion may be made from a more general grade of stainless steel, such as 303 Stainless Steel. The spring is also generally made from stainless steel. The spring may be configured to exert a force of between about 5 lbs. and 15 lbs. on the piston when the top surface of the piston is in the upmost position. In an exemplary embodiment, the spring is configured to exert a force of about 10 lbs. In some exemplary embodiments, the hollow protrusion includes a positive stop feature configured to limit an upmost position of the top surface of the piston. For example, a piston may not need to contact the bolt of the rifle at all times during firing and reloading cycles, and at certain points, a positive stop controls the extension of the piston out of the hollow protrusion. The piston may be configured to extend out of the hollow protrusion less than about 0.5 inches when the top surface of the piston is in the upmost position. 
         [0008]    The insert assembly may also include a second protrusion attached to the support plate and extending away from the front face of the support plate in the same direction as the hollow protrusion. The second protrusion includes a second top surface configured to press on an upper receiver of the rifle and exert a force on that receiver when the upper receiver is engaged with the lower receiver (i.e., when the rifle is in an assembled state). A friction created supports the insert assembly with respect to other components of the rifle. This friction may exist between the second top surface and the upper receiver as well as between the support plate and the lower receiver. The second top surface may include a rubber-like compressible material. More specifically, the second top surface may include Santoprene™ TPV 111-35. The second top surface may extend at least about 0.25 inches from the second protrusion prior to engaging with the upper receiver of the rifle. The second top surface is configured to compress by at least about 0.125 inches while engaging with the upper receiver of the rifle. 
         [0009]    In some exemplary embodiments, an insert assembly for installing into a rifle includes a support plate configured for insertion into a lower receiver of the rifle and a protrusion attached to the support plate and extending away from a front face of the support plate. The protrusion includes a second top surface configured to press on an upper receiver of the rifle and exert a force on the upper receiver when the upper receiver is engaged with the lower receiver. The friction created by this force supports the insert assembly with respect to other components of the rifle. 
         [0010]    The insert assembly may include a support plate, a hollow protrusion, a piston inserted into the hollow protrusion, a spring inserted into the hollow protrusion between the piston and the support plate, and a second protrusion attached to the support plate and having a second top surface. The support plate is configured for insertion into a lower receiver of the rifle. The hollow protrusion rigidly attaches to the support plate and extends away from a front face of the support plate. The piston is configured to slide inside the hollow protrusion in a direction substantially perpendicular to the front surface of the support plate. The piston includes a top surface for supporting a bolt of the rifle while the bolt slides over the top surface in a direction substantially parallel to the top surface. The top surface includes a chamfer configured to locate the bolt keyway when the bolt moves reciprocally between its two working positions during firing and reloading. The spring is configured to exert a predetermined force of between about 5 lbs. and 15 lbs. on the piston, thereby pushing the piston against the bolt and away from the front surface of the support plate. The second top surface of the second protrusion is configured to press on an upper receiver of the rifle and exert a force on the upper receiver when the upper receiver is engaged with the lower receiver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements. 
           [0012]      FIG. 1  is a schematic side view of a rifle. 
           [0013]      FIG. 2  is a partial schematic cross-sectional side view of a rifle assembly. 
           [0014]      FIG. 3  is a general schematic view of a bolt within a rifle. 
           [0015]      FIGS. 4A and 4B  are general schematic views of a bolt supported by an insert assembly at two different positions of the bolt. 
           [0016]      FIGS. 5A and 5B  are schematic views of an insert assembly at two different positions of its piston. 
           [0017]      FIG. 6  is a schematic perspective view of an insert assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail to not unnecessarily obscure the present invention. While the invention will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the invention to the embodiments. 
         [0019]    Various embodiments of the device are configured to improve the accuracy of small arms by removing unwanted motion from the components. While the following description refers generally to a rifle, it will be recognized that the device can also be used in small arms not generally described as a rifle. 
         [0020]    Some components of a bolt action rifle will now be briefly described in order to provide a better understanding of various claimed features.  FIG. 1  is a schematic side view of a rifle  100  that includes an upper receiver  105  pivotally coupled to a lower receiver  110 . Upper receiver  105  includes a barrel  115  that may be attached to upper receiver  105  using threaded or other types of mechanical couplings. Barrel  115  has a front sight assembly  120  securely attached thereto and is partially enclosed by a pivotable hand-guard assembly  125 . Hand-guard assembly  125  is pivotally mounted to barrel  115  using a pivot pin  165 . Barrel  115  has a gas port passing inside and through the top portion of barrel  115  to communicate with a gas cylinder assembly  130 . Certain details of the gas port and gas cylinder assembly are further described below in the context of  FIG. 2 . 
         [0021]    Upper receiver  105  and lower receiver  110  are braced by the butt-stock assembly  135 , which is attached to lower receiver  110  using threaded or other types of mechanical couplings. A handgrip  140  is attached to lower receiver  110  directly behind a trigger assembly. A removable magazine  145  is fitted into a magazine well of lower receiver  110 . A rear sight assembly  150  is adjustably mounted on upper receiver  105 . A charging handle  155  is attached to upper receiver  105  and is used to engage bolt assembly  160 . As can be seen from  FIG. 1 , a coupling between upper receiver  105  and lower receiver  110  establishes references between various other components of rifle  100 . Specifically, a reference is provided between front sight assembly  120 , rear sight assembly  150  and barrel  115  secured on upper receiver  105  with respect to butt-stock assembly  135  and handgrip  140  secured on lower receiver  110 . This reference may be important while supporting rifle  100  by butt-stock assembly  135  and handgrip  140  and aiming at a target using front sight assembly  120  and rear sight assembly  150 , particularly when firing in a continuous mode. Any slop between upper receiver  105  and lower receiver  110  may interfere with this aim and, therefore, needs to be minimized. 
         [0022]      FIG. 2  is a partial schematic cross-sectional view of a rifle assembly  200 , in accordance with certain embodiments. Assembly  200  is shown with cut-away portions of upper receiver  105  and lower receiver  110 . 
         [0023]    A bolt carrier  205  carries a bolt  210  and is slidably mounted to upper receiver  105 . Bolt carrier  205  is also affixed at the top to a gas key  215 , which is used to seal off the gas passages to bolt carrier  205 . A gas system  220  includes a cylindrical gas cylinder  225  rigidly mounted to the front sight assembly and containing therein a slidable piston  230  having a dished gas pressure face and being fixedly secured to a slidable piston rod  235 . Piston rod  235  extends concentrically down gas cylinder  225  and slidably engages a cylinder nut  240 , which is threadably engaged in the left-most end of gas cylinder  225 . Gas cylinder  225  and piston  230  may be made of a hard structural material, such as steel or stainless steel. Gas cylinder  225  is closed at the opposite end by cylinder nut  240 . The length of gas cylinder  225  varies depending upon the amount of stroke needed to completely cycle the bolt  210  and bolt carrier  205  sufficiently backward in the receiver to eject a fired cartridge and to load a new unfired cartridge into chamber  245 . Gas cylinder  225 , slidable piston  230 , and piston rod  235  are arranged to lay substantially parallel to barrel bore  250  such that piston rod  235  passes through an opening  255  formed in upper receiver  105 . Piston rod  235  extends through opening  255  and engages in passage  260 . 
         [0024]    A bolt contacts a breech and then rotates and locks into a place in which it is being held by lugs attached to the breech or to the barrel extension. Upon closing, the bolt passes through the slots cut in the front of the barrel extension and then rotates. At this point it is locked in place. The bolt remains locked until the action is cycled. This could be performed either manually by the operator or mechanically by the gas system described above in the context of  FIG. 2 . In this later example, the gas created by discharging the rifle pushes on the bolt carrier. The bolt carrier then rotates the bolt and unlocks it from the breech so that it can be withdrawn in order to extract and eject the spent casing and chamber a new round. It should be noted that rotating bolts are not exclusive to gas-operated weapons and can be found in some bolt-action, lever-action and pump-action rifle designs. As such, various inventive aspects described in this document may be applied to all bolt-type rifles. 
         [0025]    A magazine of a typical rifle includes a spring that forces bullets towards the bolt. Compression springs are typically used for this purpose. These springs provide variable forces depending on their compression levels, which in turn depend on a number of bullets remaining in the magazine. Therefore, when the magazine is fully loaded, the force may be much greater then when the magazine is almost empty. The bolt typically has some clearance, which is often referred to as “slop.” The clearance may be needed for the bolt to freely move and to avoid jamming the rifle during firing and recharging. However, a combination of this clearance and a variable force applied to the bolt may cause the bolt to operate differently at different magazine loadings. This in turn may interfere with the shooting precision as further described below. 
         [0026]      FIG. 3  is a schematic view of a rifle assembly  300  including a bolt  305 , in accordance with an exemplary embodiment. Bolt  305  is configured to move in a direction  310  between two operating positions during firing and reloading. Direction  310  is typically substantially parallel or, more specifically, substantially coaxial to a barrel of the rifle. The clearance in the bolt assembly described above allows bolt  305  to move within that assembly in other directions (e.g., a left-right direction  315  and an up-down direction  320  as shown in  FIG. 3 ). Motion of a bolt in these other directions  315  and  320  is not desirable because it may cause the entire rifle to shake and interfere with shooting accuracy, particularly when shooting in an automatic mode. A force from the magazine&#39;s spring helps to push bolt  305  to an upward position. However, this force is variable and causes variations in how much bolt  305  moves in directions  315  and  320 . A user may experience gradually increasing vibrations as he continues to shoot and empty the magazine. These vibrations abruptly disappear when the magazine is replaced and shooting is resumed. 
         [0027]    It has been found that shooting accuracy may be improved by minimizing unnecessary movements of a rifle&#39;s internal components or at least making these movements more constant and less dependent, for example, on the magazine&#39;s loading. A specific insert assembly has been designed to exert a constant force on a bolt while it moves between the two operating positions. The insert may be installed into a lower receiver of the rifle. In certain embodiments, the insert is equipped with a rubber button that pushes on the upper receiver of the rifle, thereby producing a constant force between the two receivers and preventing the receivers from moving with respect to each other. 
         [0028]      FIGS. 4A and 4B  are schematic views of a bolt  405  supported by an insert assembly  420  at two different positions of the bolt  405 , in accordance with an exemplary embodiment. In  FIG. 4A , bolt  405  is shown in a forward position. In  FIG. 4B , bolt  405  is shown in a rearward position. 
         [0029]    Bolt  405  will generally have a variable cross-sectional profile. For example, bolt  405  may have a narrow portion  410  and a wider portion  415 . While bolt  405  is movable within the rifle, insert assembly  420  is stationary. Insert assembly  420  is configured to exert a force on bolt  405  as bolt  405  moves within the rifle. The force applied is variable according to the strength of the spring selected. The applied force may be about 5 lbs., about 10 lbs, or about 15 lbs. Unlike the force from the magazine&#39;s spring which varies with the number of rounds in the magazine, the force exerted by the insert assembly is constant. The amount of applied force may be chosen by the user of the weapon. 
         [0030]      FIGS. 5A and 5B  are schematic views of an insert assembly  500  at two different positions of a piston  520 . Insert assembly  500  includes a support plate  505  configured to be received in a lower receiver of the rifle. Support plate  505  includes a top surface  510  which may be used for reference purposes. 
         [0031]    Insert assembly  500  includes a hollow protrusion  515 , which may be rigidly attached to support plate  505 . As shown in  FIG. 5A , hollow protrusion  515  may extend away from the top surface  510  of the support plate. Hollow protrusion  515  may be configured to receive a piston  520 , which may slide within hollow protrusion  515  in a direction substantially perpendicular to the top surface  510  of support plate  505 . Piston  520  has a top end extending out of hollow protrusion  515  and configured to support a bolt. The piston  520  supports the bolt as the bolt slides over the top surface of the piston  520  in a direction substantially parallel to the top surface  510  of the support plate  505 . 
         [0032]    The top surface of the piston  520  may have a chamfer  535 . Chamfer  535  may be configured to allow uneven portions of the bolt to slide over the top surface. Hollow protrusion  515  and piston  520  may include an aligning feature for controlling the orientation of chamfer  535  with respect to support plate  505 . The top surface of piston  520  is substantially parallel to front face  510  of support plate  505 . 
         [0033]    Insert assembly  500  also includes a spring  525  inserted into hollow protrusion  515  between piston  520  and top surface  510  of support plate  505 . Spring  525  may be configured to exert a predetermined force on piston  520  and push piston  520  upward relative to the top surface  510  of support plate  505 . Hollow protrusion  515  may include a positive stop feature configured to limit an upmost position of piston  520  such as a base element that contacts a lip of hollow protrusion  515 . 
         [0034]    Spring  525  may be selected to exert a force as desired by the user. The force may be between about 5 lbs. and 15 lbs. exerted on piston  520  when piston  520  is in the upmost position. 
         [0035]    Insert assembly  500  may include a second protrusion  530  attached to support plate  505  and extending away from top surface  510  in the same direction as hollow protrusion  515 . Second protrusion  530  includes a second top surface configured to support an upper receiver of the rifle and exert an upward force on the upper receiver when the upper receiver is engaged with the lower receiver. The second top surface may be made from a rubber-like compressible material, such as Santoprene™ TPV 111-35. The second top surface may extend by between about 0.25 inches from top surface  510  of support plate  505  prior to engaging with the upper receiver of the rifle. The second top surface may be configured to compress by at least about 0.125 inches while engaging with the upper receiver of the rifle. If desired for a particular application, insert assembly  500  may include only the second protrusion  530  and no hollow protrusion  515 , piston  520 , or spring  525 . 
         [0036]      FIG. 6  is a schematic perspective view of an insert assembly  500  in accordance with an exemplary embodiment. Specifically, the support plate  505  is shown as having the top surface  510  with the hollow protrusion  515  positioned on the top surface  510 . The hollow protrusion  515  is shown as receiving the piston  520 , which may expand and contract within the hollow protrusion  515  in a direction substantially perpendicular to the top surface  510  of the support plate  505 . The piston  520  has a top surface which extends beyond the hollow protrusion  515 . Furthermore, the top surface of the piston  520  is shown as including the chamfer  535 . 
         [0037]    As mentioned above, the hollow protrusion  515  and the piston  535  may include aligning features for controlling orientation of the chamfer  535  with respect to the support plate  505 .  FIG. 6  shows a slideable arrangement of a channel on the hollow protrusion  515  and a guide on the piston  520  used for alignment. The chamfer  535  may be used to allow portions of the bolt to slide over the top surface as illustrated in  FIGS. 4A and 4B . The chamfer  535  may be also used to locate the bolt keyway when the bolt moves reciprocally between its working positions during firing and reloading. 
         [0038]    The insert assembly  500  may also include the spring  525  inserted into the hollow protrusion  515  between the piston  520  and the top surface  510  of the support plate  505 . The spring  525  may be configured to exert a predetermined force on the piston  520  and push the piston  520  upward relative to the top surface  510  of the support plate  505 , thereby providing a stabilizing force for the bolt of the weapon. 
         [0039]    The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. While the present invention has been described in connection with a series of embodiments, these descriptions are not intended to limit the scope of the invention to the particular forms set forth herein. It will be further understood that the invention is not necessarily limited to the discrete features or the order of the features described. To the contrary, the present descriptions are intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and otherwise appreciated by one of ordinary skill in the art.