Patent Publication Number: US-9885529-B2

Title: Contoured cam pin for a rotating bolt

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional patent application Ser. No. 62/217,149, filed Sep. 11, 2015, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure pertains generally to firearms. In particular, the present disclosure provides an improved cam pin for a bolt carrier system of a firearm. 
     The M16 rifle is a standard weapon of choice for many institutions around the world including the U.S. military and many law enforcement agencies. Over the years the M16 has been modified to include a large family of weapons including semi-automatic counterparts which are popular in the civilian sector. Additionally, the M16 design has been scaled up from a .223 (5.56 mm) caliber bullet to 7.62 mm NATO and .308 Winchester as well as shortened into the more compact M4 carbine version of the M16. 
     Generally, the M16 family of automatic and semi-automatic rifles is based on a gas operated rotating bolt carrier system. The bolt carrier includes a multi-lug bolt that interlocks with corresponding lugs within a barrel extension engaged to the barrel to contain the firing of each round of ammunition. The bolt carrier system includes a rotating mechanism that locks the bolt into place with respect to the barrel extension during the loading step and also includes a corresponding unlocking motion when extracting a spent casing. The bolt includes a spring loaded extractor configured to releasably engage a cartridge as it is loaded into the firing chamber. When the rifle is fired, the interlock bolt contains the firing force by transmitting the force through the lugs to corresponding lugs of the barrel extension. 
     When a round is fired, gas pressure is vented from a port in the barrel down from the firing chamber and that gas pressure is applied to the bolt carrier system to impart energy in a rearward direction. As the bolt carrier system moves rearwardly, it first rotates the bolt to unlock the bolt lugs from the barrel extension lugs. Then, as it further recoils, the extractor pulls the expended cartridge from the firing chamber. Once the cartridge clears the firing chamber an ejector in the bolt pivots the cartridge about the extractor and ejects the spent cartridge, as is well known in the art. As the bolt carrier system continues to move rearwardly its travel is halted by a spring that then pushes the bolt carrier system forward to engage and chamber another round. This process is repeated as often as desired by a shooter until the last cartridge in a magazine is expended. 
     Under repeated firing and cycling of the bolt carrier system, some components of the bolt carrier system slide and impact other components of the bolt carrier system, causing wear on at least some of the components. In particular, cam pins of existing bolt carrier systems have been found to suffer from wear which may lead to failure of the cam pin. Thus, there is a desire for cam pins that are wear resistant. 
     SUMMARY 
     The present disclosure pertains generally to cam pins for rotating bolt firearms. In certain aspects, the present disclosure provides cam pins having a head portion and an elongate body extending from the head portion, the elongate body having a cam slot engaging segment and a bolt engaging segment, the cam slot engaging segment having a first portion with a first cross-sectional dimension and a second portion with a second cross-sectional dimension, the first cross-sectional dimension being greater than the second cross-sectional dimension, and the first portion being located between the head portion and the second portion. In some instances, the present disclosure provides an improved cam pin for a bolt carrier system of a rotating bolt firearm, the cam pin having a head portion and an elongate body extending from the head portion, wherein the improvement comprises the elongate body having a sloped, curved, and/or stepped profile along a length of the elongate body adjacent to the cam slot of a bolt carrier when the cam pin is inserted into a bolt and bolt carrier. 
     The present disclosure also provides bolt carrier group kits comprising a bolt carrier defining a cam slot; a bolt including a lug and defining a cam pin opening, the bolt slidably and rotatably receivable within the bolt carrier; and a cam pin having a head portion and an elongate body extending from the head portion, wherein the elongate body having a cam slot engaging segment and a bolt engaging segment; wherein the cam slot engaging segment engages with the cam slot when the cam pin is received in the cam pin opening and the bolt is received in the bolt carrier; wherein the cam slot engaging segment has a first portion with a first cross-sectional dimension and a second portion with a second cross-sectional dimension; wherein the first cross-sectional dimension is greater than the second cross-sectional dimension; and wherein the first portion is located between the head portion and the second portion. 
     The present disclosure also provides rotating bolt firearms comprising a lower receiver; an upper receiver coupled to the lower receiver; a barrel assembly coupled to the upper receiver; a bolt carrier group assembly movably received in the upper receiver, the bolt carrier group assembly including a bolt carrier and a bolt assembly; a cam pin having a head portion and an elongate body extending from the head portion, wherein the elongate body has a cam slot engaging segment and a bolt engaging segment; wherein the bolt carrier defines a cam slot; wherein the bolt assembly includes a lug and is slidably and rotatably positionable within the bolt carrier and wherein the bolt assembly defines a cam pin opening; wherein the cam pin is received in the cam pin opening and is positioned in and engagable with the cam slot; wherein the cam slot engaging segment has a first portion with a first cross-sectional dimension and a second portion with a second cross-sectional dimension; wherein the first cross-sectional dimension is greater than the second cross-sectional dimension; and wherein the first portion is located between the head portion and the second portion. 
     In some instances, the cam pin has a sloped, curved, and/or stepped profile along a length of the cam pin that includes both the first and second portions and contacts sides of a cam slot in a bolt carrier. Additionally or alternatively, the cam slot engaging segment can have a cross-sectional dimension equal to or less than a cross-sectional dimension of the bolt engaging segment. In some instances, the cam slot engaging segment has a central portion, a first end, and a second end; the first end positioned between the central portion and the head portion and the second end positioned between the central portion and the bolt engaging portion; and wherein the central portion of the cam slot engaging segment has a greater cross-sectional dimension than the first end of the cam slot engaging segment. In some instances, the central portion of the cam slot engaging segment has a greater cross-sectional dimension than the bolt engaging segment. 
     It is intended that the herein disclosed improvement to cam pins can be used with U.S Military and NATO M16 bolts and bolt carriers including M4 variants and weapons based on the M16 design but chambered in different calibers such as 7.62 NATO. It should also be understood that the improved cam pins disclosed herein can be used with other weapon systems that utilize a rotating bolt and a cam pin arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective assembly view of a rifle incorporating an exemplary bolt carrier system. 
         FIG. 2  is a perspective view of a forward end of a bolt carrier group assembly with the bolt in an extended, unlocked configuration. 
         FIG. 3  is a perspective view of a forward end of a bolt carrier group assembly with the bolt in a retraced, locked configuration. 
         FIG. 4  is a top view of a forward portion of a bolt carrier. 
         FIG. 5  is a front perspective view of a bolt assembly and cam pin. 
         FIG. 6  is a back perspective view of the  FIG. 5  bolt assembly and cam pin. 
         FIG. 7  is a front elevational view of a cam pin. 
         FIG. 8  is a side elevational view of the cam pin of  FIG. 7 . 
         FIG. 9  is a bottom plan view of the cam pin of  FIG. 7 . 
         FIG. 10  is a perspective view of another cam pin. 
         FIG. 11  is a front elevational view of the cam pin of  FIG. 10 . 
         FIG. 12  is a side elevational view of the cam pin of  FIG. 10 . 
         FIG. 13  is a bottom plan view of the cam pin of  FIG. 10 . 
         FIG. 14  is a cross-sectional view of a bolt carrier group assembly of  FIG. 1  taken along line  14 - 14  with the cam pin of  FIG. 10 . 
         FIG. 15  is a close-up view of the cam pin portion of  FIG. 14 . 
         FIG. 16  is a close-up view of the cam-slot engaging section of the cam pin of  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity. 
     With respect to the specification and claims, it should be noted that the singular forms “a”, “an”, “the”, and the like include plural referents unless expressly discussed otherwise. As an illustration, references to “a device” or “the device” include one or more of such devices and equivalents thereof. It also should be noted that directional terms, such as “up”, “down”, “top”, “bottom”, and the like, are used herein solely for the convenience of the reader in order to aid in the reader&#39;s understanding of the illustrated embodiments, and it is not the intent that the use of these directional terms in any manner limit the described, illustrated, and/or claimed features to a specific direction and/or orientation. 
     Referring to  FIG. 1 , a rifle  100  is illustrated. Rifle  100  is configured for use with 7.62 mm×51 mm NATO rounds and is similar in some respects to versions configured for .308 Winchester and 5.56 mm×45 mm NATO rounds. The illustrated rifle is manufactured by Lewis Machine &amp; Tool Co. in Milan, Ill. Rifle  100  includes lower receiver  102 , integral upper receiver and hand guard portion  104 , barrel assembly  106  and bolt carrier group assembly  108 . Lower receiver  102  includes stock  110 , trigger assembly  112 , magazine  114  and handle  116 . 
     Integral upper receiver and hand guard portion  104  includes upper receiver portion  118  and hand guard portion  120 . An upper rail  122  extends across upper receiver portion  118  and hand guard portion  120 . In the illustrated embodiment, integral upper receiver and hand guard portion  104  is unitarily constructed of a single piece. However in other embodiments, integral upper receiver and hand guard portion  104  may be constructed from a plurality of pieces joined together. In yet other embodiments, integral upper receiver and hand guard portion  104  may be replaced with a conventional upper receiver and detachable hand guard portion as is well known in the art. 
     Referring now to  FIG. 2-3 , bolt carrier group assembly  108  includes a bolt carrier  130 , a bolt assembly  132 , and a cam pin  134 . Bolt assembly  132  is slidably and rotatably mounted in bolt carrier  130 . Bolt assembly  132  includes a bolt  140  having lugs  144  at the forward end of bolt  140  that releasably interlock with a portion of barrel assembly  106 . A firing pin (not shown) extends through a central bore through bolt  140 . Cam pin  134  extends through a cam slot  150  defined in bolt carrier  130  and extends into a cam pin opening  146  in bolt  140  (as shown in  FIGS. 5 and 6 ). 
     As best shown in  FIG. 4 , Cam slot  150  extends longitudinally along and circumferentially around a portion of bolt carrier  130 . When bolt carrier group assembly  108  is in an unlocked configuration, as shown in  FIG. 2 , bolt assembly  132  is in an extended position from the end of bolt carrier  130  and cam pin  134  is positioned at a forward end of cam slot  150 . When bolt carrier group assembly  108  is in a locked configuration, as shown in  FIG. 3 , bolt assembly  132  is in a retracted position and cam pin  134  is positioned at a rearward end of cam slot  150 . As bolt assembly  132  transitions between the unlocked and locked configurations, cam pin  134  travels along a locking cam path, contacting and sliding along sides  152  of cam slot  150 , causing bolt assembly  132  to rotate about and move along longitudinal axis  170  of bolt carrier  130 . For example, with reference now to  FIG. 4 , cam slot  150  includes locked position  154 , unlocked position  156 , forward edge  158 , unlocking cam path  160 , delay ridge  162 , end of unlock dwell  164 , locking cam path  166 , and delay ridge  168 . In the locked configuration, cam pin  134  is located at locked position  154 . In the unlocked configuration, cam pin  134  is located at unlocked position  156 . As bolt assembly  132  moves from locked position  154  to unlocked position  156 , cam pin  134  slides past delay ridge  168  and along unlocking cam path  160  into unlocked position  156 , eventually coming into contact with forward edge  158 . As bolt assembly  132  moves from unlocked position  156  into locked position  154 , cam pin  134  slides past delay ridge  162  and along locking cam path  166  into locked position  154 . 
       FIGS. 5 and 6  illustrate the cooperation of bolt  140  and a cam pin  234 . As mentioned above, cam pin  234  extends into cam pin opening  146  defined in bolt  140 . Rotation of cam pin  234  around longitudinal axis  170  of bolt carrier  130  causes rotation of bolt  140  around longitudinal axis  170 . Therefore, as cam pin  234  moves along a length of bolt carrier  130  and contacts sides  152  of cam slot  150 , cam pin  234  rotates around longitudinal axis  170  and bolt  140 , in turn, rotates around longitudinal axis  170  so that lugs  144  of bolt  140  can lock or unlock with a barrel extension (not shown). 
     A prior art cam pin  234  that was subjected to extended use testing by Applicant is illustrated in  FIGS. 7-9 . Cam pin  234  has a head portion  180  and a cylindrical body portion  182 . Head portion  180  has a generally rectangular cross-sectional shape defining side surfaces  190 ,  192 ,  194 , and  196 . When bolt carrier group assembly  108  is in the unlocked configuration, head portion  180  is slidably received within a gas key and charging handle groove defined in upper receiver portion  118 . 
     Cylindrical body portion  182  includes a bolt engaging segment  200  and a cam-slot engaging segment  202 . Bolt engaging segment  200  defines an aperture  204  for receiving a firing pin and is sized and arranged to be received within cam pin opening  146  of bolt  140 . Cam-slot engaging segment  202  is arranged to slidably engage portions of cam slot  150  when bolt assembly  132  is received within bolt carrier  130  and bolt engaging segment  200  of cam pin  234  is received within cam pin opening  146  of bolt  140 . 
     Applicant found that a cam pin can experience fretting and/or galling along cam slot engaging segment  202  from the repeated cycling of the firearm. For instance, Applicant has observed wear marks  220  on the portions of cam slot engaging segment that slide along sides  152  of cam slot  150 . Furthermore, Applicant observed increased  220  wear along cam slot engaging portion nearer head portion than bolt engaging segment. Applicant considers this to be likely due to the cam slot engaging portion being farther away from the axis of rotation (i.e., longitudinal axis  170 , such as the firing pin) and therefore having to travel a greater distance during rotation than portion(s) of cam pin  234  located closer to the longitudinal axis  170 . 
     Additionally, as cam pin  234  rotates around longitudinal axis  170 , portions of cam pin  234  positioned farther from longitudinal axis  170  travel at a greater velocity around longitudinal axis  170  than portions of cam pin  234  positioned nearer to longitudinal axis  170 . This results in a velocity gradient along a length of cam pin  234  and, in particular, along cam slot engaging segment  202 . Accordingly, portions of cam slot engaging segment  202  slide along sides  152  of cam slot  150  at velocities of different magnitude and travel different distances each actuation. This, Applicant believes, causes a relative shear stress along portions of cam slot engaging segment  202 , increasing the likelihood of and/or instance of fretting and/or galling and possibly the release of metal particles into the action of rifle  100 , which may potentially result in and/or contribute to a weapon malfunction. 
     Wear marks  220  along cam slot engaging segment  202  found during Applicant&#39;s testing is shown in  FIGS. 7 and 8 . In some instances, this wear may result in increased friction between bolt carrier  130  and cam pin  234  and/or structural failure of cam pin  234 , possibly resulting in a malfunction of the firearm. To address this issue, Applicant developed novel cam pin  134  shown in  FIGS. 10-13 . Cam pin  134 , as shown in  FIGS. 10-13 , has a head portion  180  and a cylindrical body portion  182 . Head portion  180  has curved and linear side surfaces  250 ,  252 ,  254 , and  256 , with opposing sides  252  and  256  being linear and parallel with opposing side surfaces  250  and  254  being curved. 
     Cylindrical body portion  182  includes a bolt engaging segment  200  and a cam-slot engaging segment  202 . Cylindrical body portion  182  has a length and a profile that includes linear portions, curved portions, and/or stepped portions along a portion of the length. Bolt engaging segment  200  defines an aperture  204  for receiving a firing pin and is sized and arranged to be received within cam pin opening  146  of bolt  140 . Cam-slot engaging segment  202  is arranged to slidably engage portions of sides  152  in cam slot  150  when bolt assembly  132  is received within bolt carrier  130  and bolt engaging segment  200  of cam pin  134  is received within cam pin opening  146  of bolt  140 . 
     As shown in  FIGS. 10-16 , cam slot engaging segment  202  has a curved profile. Central portion  260  of cam slot engaging segment  202  has a cross-sectional dimension  300  (e.g., diameter) measured in a cross-sectional plane of cam pin  134 . End portion  262  of cam slot engaging segment  202  near bolt engaging segment  200  has a cross-sectional dimension  302 , and end portion  264  of cam slot engaging segment  202  near head portion  180  has a cross-sectional dimension  304 . Both cross-sectional dimension  302  and cross-sectional dimension  304  are less than cross-sectional dimension  300  of central portion  260 . In this way, cam slot engaging segment  202  only contacts sides  152  of cam slot  150  along central portion  260 , which reduces the magnitude of the velocity gradient along the length of cam pin  134  that contacts sides  152  of cam slot  150 , potentially reducing the likelihood and/or instance of fretting and/or galling. 
     While the above embodiments have been illustrated and described with the cam slot engaging portion having a curved profile, it is contemplated that the cam slot engaging segment may additionally or alternatively include a stepped, sloped, tapered or otherwise shaped profile. 
     While the present disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that a preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the invention defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein. 
     The language used in the claims and the written description and in the above definitions is to only have its plain and ordinary meaning, except for terms explicitly defined above. Such plain and ordinary meaning is defined here as inclusive of all consistent dictionary definitions from the most recently published (on the filing date of this document) general purpose Merriam-Webster dictionary. 
     As used in the claims and the specification, the following terms have the following defined meanings: 
     The term “curvilinear” as used herein has the meaning, having at least one curve. It includes, but is not limited to, being fully curved as well as including one or more linear segments. It includes curves with a constant radius as well as non-constant radii of curvature. 
     The term “fretting” as used herein has the meaning, damage induced under load and in the presence of repeated surface motion. Fretting tangibly downgrades the surface layer quality, producing increased surface roughness and micropits, which reduces the fatigue strength of the components. 
     The term “galling” as used herein has the meaning, wear caused by adhesion between sliding surfaces that causes material of a first surface to be pulled with the contacting surface. Galling can, in many instances, leave some material from a first surface attached to the contacting second surface, potentially appearing as a bulge on the second surface with a gouge in the first surface. 
     The term “M16” as used herein includes military, civilian, semi-automatic and automatic versions of the M16 rifle. This includes but is not limited to the AR-15, M16A1, M16A2, M16A3, M16A4 and M4A1 rifles. The term “M16,” as used herein, is inclusive of versions of the M16 rifle chambered for .223 Remington, 5.56 NATO, 7.62 NATO, and .308 Winchester and as well as pistol versions (i.e., versions without a buttstock) and short-barreled rifle (“SBR”) versions as similar bolt carrier assembly are used in all these variants. 
     The term “profile” as used herein has the meaning, the outline shape of an object along its length. The term includes the silhouette of an object. 
     The term “wear” as used herein has the meaning, the removal and/or deformation of material on a surface as a result of mechanical interaction with an interfacing surface. The term includes a loss of dimension from plastic deformation as well as impact or impulse wear.