Patent Publication Number: US-11656042-B2

Title: Bolt assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation-in-Part of U.S. patent application Ser. No. 17/019,686 filed on Sep. 14, 2020 entitled “B.L.T. BOLT CARRIER,” which is a Continuation-in-Part of U.S. patent application Ser. No. 15/718,081 filed on Sep. 28, 2017, entitled “B.L.T. BOLT CARRIER,” which claims the benefit of U.S. Provisional Patent Application No. 62/400,826 filed on Sep. 28, 2016, entitled “BLT Bolt Carrier,” which are hereby incorporated by reference in their entirety for all that is taught and disclosed therein. 
     U.S. patent application Ser. No. 17/019,686 filed on Sep. 14, 2020 entitled “B.L.T. BOLT CARRIER” also claims the benefit of U.S. Provisional Patent Application No. 62/906,161 filed on Sep. 26, 2019, entitled “B.L.T. Bolt Carrier,” which is hereby incorporated by reference in its entirety for all that is taught and disclosed therein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to firearms, and more particularly to a bolt assembly that enables pistol variants of the AR-15, as well as standard versions of the AR-15, M16 and M4 rifle and other firearm platforms that have the same dimensions to fit this invention, to omit an extension tube to reduce length, fire while folded/collapsed, or use a module-type stock. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Normal AR-15, M16 and M4 rifles have an extension tube that extends to the rear of the upper receiver and contains the recoil spring. Given the length of the bolt carrier, the recoil spring needs the additional length supplied by the extension tube to compress and provide an adequate range of motion of the bolt carrier. The travel of the buffer to the rear of the extension tube causes the weapon to have more felt recoil due to more mass at the rear of the weapon, which is a disadvantage of a standard AR-15 recoil assembly. While the standard AR-15 recoil assembly is suitable for AR-15 rifles with normal shoulder stocks, the protruding extension tube is a problem for pistol variants of the AR-15 firearm platform, as well as for standard AR-15 rifles having folding, fully collapsing stocks, or modular stocks, which are incompatible with a fixed extension tube. 
     Therefore, a need exists for a new and improved bolt assembly that enables pistol variants of the AR-15 firearm platform to omit an extension tube to reduce length. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the bolt assembly according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of enabling variants of the AR-15 firearm platform to omit an extension tube to reduce length and enable the firearm to fire while folded or fully collapsed. 
     The present invention provides an improved bolt assembly, and overcomes the above-mentioned disadvantages and drawbacks of the prior art. As such, the general purpose of the present invention, which will be described subsequently in greater detail, is to provide an improved bolt assembly that has all the advantages of the prior art mentioned above. 
     To attain this, the preferred embodiment of the present invention essentially comprises a rear block configured for connection at the rear end of the bolt passage, a bolt carrier configured to reciprocate in the bolt passage, a support element between the rear block and the bolt carrier, a first spring between the support element and the rear block, the bolt carrier defining a bore, the support element including a guide rod slidably received in the bore, and a second spring encompassing the guide rod, having a rear end abutting the support element, and a forward portion received in the bore. The bolt carrier may include a bolt carrier body, and the bolt carrier may include a weight portion movably connected to the bolt carrier body. The weight portion may define a through hole receiving an intermediate portion of the guide rod and an intermediate portion of the second spring. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front exploded view of the current embodiment of a bolt assembly constructed in accordance with the principles of the present invention. 
         FIG.  2    is a rear assembled view of the bolt assembly of  FIG.  1   . 
         FIG.  3    is a side sectional view of the bolt assembly of  FIG.  1    in the forward battery condition. 
         FIG.  4    is a side sectional view of the bolt assembly of  FIG.  1    in the forward battery condition. 
         FIG.  5    is a side sectional view of the bolt assembly of  FIG.  1    in the rearward recoil condition. 
         FIG.  6    is a front isometric view of the bolt assembly of  FIG.  1    in the forward battery condition. 
         FIG.  7    is a front isometric view of the bolt assembly of  FIG.  1    in the rearward recoil condition. 
         FIG.  8    is a front isometric view of the bolt carrier of  FIG.  1    in the forward battery condition. 
         FIG.  9    is a side sectional view of the bolt carrier of  FIG.  1    in the forward battery condition with the slide weight in the closed position. 
         FIG.  10    is a front isometric view of the bolt carrier of  FIG.  1    with the slide weight in the open position after absorbing kinetic energy of the bolt, thereby reducing bolt. 
         FIG.  11    is a side sectional view of the bolt carrier of  FIG.  1    with the slide weight in the open position after absorbing kinetic energy of the bolt, thereby reducing bolt bounce. 
         FIG.  12    is a top sectional view of the bolt assembly of  FIG.  1    in the forward battery condition. 
     
    
    
     The same reference numerals refer to the same parts throughout the various figures. 
     DESCRIPTION OF THE CURRENT EMBODIMENT 
     An embodiment of the bolt assembly of the present invention is shown and generally designated by the reference numeral  10 . 
       FIGS.  1 - 7  and  12    illustrate the improved bolt assembly  10  of the present invention. More particularly, the bolt assembly is suitable for use with a firearm frame/upper receiver  200  defining an elongated bolt passage  202  having a rear end  204  and a forward end  206 . The bolt assembly is shown in the forward battery position in  FIGS.  3 ,  4 ,  6 , and  12    and in the rearward recoil position in  FIGS.  5  and  7   . The bolt assembly has a rear block  12  configured for connection at the rear end of the elongated bolt passage, a bolt carrier  14  configured to reciprocate in the bolt passage, a rear support element  16  that incorporates a rear-facing bump stop  124  for the bolt carrier between the rear block and the bolt carrier, and a first spring  18  between the support element and the rear block. The bolt carrier defines a pair of parallel first and second bores (right bore  20  and left bore  158  are visible in  FIG.  12   ). The rear support element includes a pair of parallel guide rods (right and left guide rods  22 ,  24 ) slidably received in the right and left bores. A pair of parallel right and left second springs  26 ,  28  encompass the right and left guide rods. The right and left second springs each have a rear end  30 ,  32  abutting the rear support element and a forward portion  34 ,  36  received in the right and left bores. The bolt carrier includes a bolt carrier body  38  with a dust cover cutout  192  and the bolt carrier includes a weight portion  40  movably connected to the bolt carrier body. The weight portion defines a pair of parallel through holes (right and left through holes  42 ,  44 ), each receiving an intermediate portion  46 ,  48  of the right and left guide rods and an intermediate portion  50 ,  52  of the right and left second springs. 
     The right bore  20  of the bolt carrier has a rear portion  54  having a rear diameter  56  sized to closely and slidably receive the forward portion  34  of the right second spring  26 , and a smaller forward portion  58  with a forward diameter  60  sized to closely receive the right guide rod  22 , with a step surface  62  in the right bore upon which a forward end  64  of the right second spring bears. Thus, the forward end of the right second spring bears on the bolt carrier body  38  well forward of the rear  90  of the bolt carrier body, thereby telescoping the right second spring within the length of the bolt carrier body and reducing the operating length of the bolt carrier assembly  10 . The left bore  158  of the bolt carrier has a rear portion  160  having a rear diameter  162  sized to closely and slidably receive the forward portion  36  of the left second spring  28 , and a smaller forward portion  164  with a forward diameter  166  sized to closely receive the left guide rod  24 , with a step surface  168  in the left bore upon which a forward end  170  of the left second spring bears. Thus, the forward end of the left second spring bears on the bolt carrier body well forward of the rear of the bolt carrier body, thereby telescoping the left second spring within the length of the bolt carrier body and reducing the operating length of the bolt carrier assembly  10 . The first spring  18  defines a first axis  68 , and the right and left second springs define right and left second axes  70 ,  72 , the first axis and right and left second axes being at the same level to define a horizontal plane  74  when the firearm frame/upper receiver  200  is in an upright operational orientation. The rear support element  16  includes a first spring alignment element/first spring engagement facility  76  configured to retain the first spring on a first spring axis  78 . The first spring is oriented on the first spring axis in registration with the first spring alignment element/first spring engagement facility. The right and left guide rods define respective second and third axes (right and left guide rod axes  80 ,  82 ). The first axis, first spring axis, and the second and third axes define a common plane (horizontal plane  74 ). The second and third axes are lateral to the first axis and first spring axis. The second and third axes are on opposite sides of the first axis and first spring axis. 
     The bolt carrier body  38  has a top  84 , bottom  86 , front  88 , and rear  90 . A gas key  92  is attached to the top by two set screws  172 . The top also defines a cam slot  94  that receives a cam pin  96 . The front defines a central bore  98  that receives the rear  100  of a bolt  102 . A forward portion  104  of the bolt extends beyond the front of the bolt carrier body to engage a United States military standard specification (milspec) or otherwise standard barrel  188  having a rear chamber  190 . The central bore in the bolt carrier body extends the length of the bolt carrier body such that the rear of the bolt carrier body receives a firing pin plunger  106 , firing pin plunger spring  108 , and firing pin  110 . The firing pin is retained by firing pin retaining pin  174 . The weight portion  40  defines a slot  112  to permit the firing pin to access the firing pin plunger and the rear of the bolt. The weight portion is slidably connected to the rear of the bolt carrier body and is biased rearwardly by a weight portion spring  114 . The cam pin, central bore, bolt, set screws, firing pin, and firing pin retaining pin are all made to United States military standard specifications (milspec) in the current embodiment. 
     A front support element  116  having right and left through holes  118 ,  120  is located between the weight portion  40  and the rear support element  16 . The right and left through holes permit passage of the right and left guide rods  22 ,  24 , but do not permit passage of the right and left second springs  26 ,  28 . Thus, the right and left second springs bias the front support element and rear support element  16  away from the weight portion  40  of the bolt carrier  14 . The front support element includes bump stops  122  that extend forwardly through through holes  186  so as to be positioned between the front support element and the weight portion and secured by rear support element  16  when secured by screw  178 . A bump stop  124  is positioned between the rear support element  16  and the rear block  12 . The bump stop is secured by spring pin  176 . A screw  178  connects the front and rear support elements with bump stop  122  in between the front and rear support elements and extending through through holes  186 . The rear block has a forward threaded portion  126  to configure the rear block for connection to the firearm lower milspec frame/receiver (not shown) on existing threads where a milspec/standard buffer tube might normally be attached at the rear end of a milspec/standard lower frame/receiver. In the current embodiment, the threaded portion has a 1 3/16″-16 tpi pitch to match a milspec/standard lower frame/receiver. Thus, the rear block becomes the rear wall when attached to the firearm lower frame/receiver and a fixed frame of reference the bolt carrier  14  reciprocates with respect to. An adapter interface mount  128  connects an adapter interface  130  to the firearm frame by the rear block  12  securing the adapter interface mount to the lower frame/receiver. The adapter interface is secured to the adapter interface mount by screw  180 . The adapter interface includes a 1913-style Picatinny rail  132 , but other styles of adapter mounts can be substituted on the adapter interface mount  128  to accommodate a greater variety of stock variants or other accessories to be attached to the firearm frame. The rear block  12  defines a first spring pocket  134  that receives the rear end  136  of the first spring  18 . The forward end  138  of the first spring abuts a flange  140  on the rear support element  16 . The adapter interface defines a rear block pocket  142  that receives the rear end  144  of the rear block. The rear end of the rear block includes a socket head  184  to facilitate threadedly securing the rear block to the firearm lower frame/receiver. A recoil assembly catch  146  attaches into the milspec/standard upper receiver  200  to prevent overtravel of the bolt carrier. The recoil assembly catch is held tightly in place in the firearm frame/upper receiver by set screw  182 . 
     Referring now to  FIG.  5   , it should be appreciated that in the rear recoil position, the components of the bolt carrier assembly are arranged in the following order from rear to front: the Picatinny rail  132 , the adapter interface  130 , the rear end  144  of the rear block  12 , the rear of the first spring pocket  134 , the rear end  136  of the first spring  18 , the bump stop  124 , the first spring engagement facility  76  on the rear support element, the adapter interface mount  128 , the front end  138  of the first spring, the flange  140  on the rear support element, the rear ends  150 ,  152  of the right and left guide rods  22 ,  24 , the threaded portion  126  of the rear block, the front support element  116 , the bump stops  122 , the rear ends  30 ,  32  of the right and left second springs  26 ,  28 , the weight portion  40 , the rear  90  of the bolt carrier body  38 , the forward ends  64 ,  66  of the right and left second springs, the forward ends  154 ,  156  of the right and left guide rods, the front  88  of the bolt carrier body, and the forward portion  104  of the bolt  102 . 
     As is shown in  FIG.  7   , the bolt carrier  14  reaches the rearward recoil position in the same distance as a conventional AR-15 rifle with an extension tube. In fact, the shorter than standard bolt carrier operates fully within the limited length of an AR-15 firearm frame and does not require an extension tube. In the current embodiment, the bolt carrier is 2.5 inch shorter than a standard bolt carrier. Elimination of the extension tube, which ranges from 3.25 inch for a carbine extension tube to 6.0 inch for a rifle-length extension, shortens the overall firearm. 
     Furthermore, because of the multispring resonance in the operating distance, the weight of the bolt carrier assembly  10  operates closely to the center axis of the firearm frame  200 . This reduces the recoil sensation felt by the user because muzzle flip is reduced. The use of multiple springs in the current invention instead of the much longer single rear spring used in a conventional AR-15 rifle has multiple advantages. First, the current invention enables the recoil forces to be absorbed closely along the center axis of the firearm. Second, the current invention prevents problems associated with stacking the coils of a longer spring against each other that would otherwise occur with such a short bolt carrier. Hammer interference would also occur if a traditional single spring was used. The first spring and right and left second springs are essentially end to end, and the entire first spring remains to the rears of the entire right and left second springs in all conditions. The first spring and right and left second springs are serially connected with the front and rear support elements  116 ,  16  compressed between them, and each of the springs has a size and shape to closely fit within the space provided for that spring within the bolt carrier assembly  10 . 
       FIGS.  8 - 11    illustrate the improved bolt carrier  14  of the present invention. More particularly,  FIGS.  8  and  9    show the bolt carrier in the forward battery position, and  FIGS.  10  and  11    show the bolt carrier with the weight  40  in the open position from absorbing the kinetic energy, thereby reducing bolt bounce. In the forward battery position, the weight portion spring  114  held in top pocket half  184  in the weight portion  40  and bottom pocket half  186  in the bolt carrier body  38  biases the weight portion  40  pushes forward to close a gap  148  between the weight portion and the rear  90  of the bolt carrier body  38 . In the recoil condition, recoil forces push the bolt carrier body rearward, which compresses right and left second springs  26 ,  28  (not shown) and first spring  18 . Compression eventually stops rearward movement of the bolt carrier when the bolt carrier has reached the rearward recoil position. When the bolt carrier and bolt  102  are locked into battery, the weight  40  absorbs the kinetic energy of the assembly and separates from the rear  90  of the bolt carrier, thus creating a gap  148 . The gap ensures the bolt carrier maintains proper lock and reduces bolt bounce, creating a dead blow effect. In some circumstances and operations, the weight&#39;s operation is reversed and the gap  148  is normally open, the weight portion spring  114  is held by the bolt carrier and pushes the weight  40  open. In the recoil condition, recoil forces push the bolt carrier body rearward, which compresses the weight portion spring and right and left second springs  26 ,  28  (not shown). The compression of the three springs causes the gap between the weight portion and the rear of the bolt carrier body to close such that the bolt carrier body impacts the weight portion, which slows the bolt carrier body. The bolt carrier body also transfers rearward force through the weight portion onto the components rearward of the weight portion. Compression of the first spring  18  and second springs  26 ,  28  eventually stops rearward movement of the bolt carrier when the bolt carrier has reached the rearward recoil position. When the bolt carrier is returning to the forward battery condition and stripping the next round from the magazine (not shown), the weight portion spring separates the weight portion from the rear of the bolt carrier body to restore the gap. When the bolt carrier and bolt  102  lock into battery, the weight portion continues forward from the inertia, compresses the weight portion spring, and impacts the rear of the bolt carrier body. Thus, the weight portion gives a dead blow effect to the bolt carrier body, thereby ensuring proper lockup and reducing bolt bounce. The weight portion spring then restores the gap. In both methods of weight  40  operation, the weight portion travels on a linear path between the two positions illustrated in  FIGS.  8  and  9  and  10  and  11   . The spring pressure exerted by the weight portion spring causes the gap between the weight portion and the rear of the bolt carrier body to be between 0.05″ and 0.25″ depending on the host firearm&#39;s characteristics (caliber, barrel length, and whether a suppressor is used). The weight portion is secured by the gas key  92  in the current embodiment, but can also be secured using other approaches if the bolt carrier has an integrated gas key or a modified gas system. 
       FIGS.  1 ,  3 ,  5  and  12    illustrate the improved firing pin safety feature. In a traditional milspec bolt carrier, the firing pin  110  is a free float design. To add a modern safety feature, the invention includes a spring plunger  106  with a plunger spring  108  in front of the firing pin to eliminate the free float firing pin. 
     Bolt carrier  38  may or may not have a dust cover cutout  192  depending on user preference. The bolt carrier may have a modified half cutout to keep guide rod bore  20  safe from the elements, or the bolt carrier may have a standard full-size cutout, (not shown, guide rod bore  20  is visible) depending on consumer preference. The dust cover cutout can be designed to use milspec/standard dust covers (not shown). A modified half dust cover cutout needs a dust cover with a modified detent footprint to fit the half dust cover cutout. A detent and spring are held in place by a wire clip or detent pressed into place with or without a wire clip. Instead of the normal milspec detent length of about ½ inch, the length of the detent for the modified half dust cover needs to be ¼ inch or smaller to fit the half dust cover cutout. Along with a smaller detent footprint, the modified half dust cover needs the modified shortened detent and a new means of securing the detent using a wire clip, a press fit, or both. All other dimensions of the half dust cover are standard and a standard way of securing the cover to the frame/upper receiver is used. 
     In the context of the specification, the terms “rear” and “rearward,” and “front” and “forward,” have the following definitions: “rear” or “rearward” means in the direction away from the muzzle of the firearm while “front” or “forward” means it is in the direction towards the muzzle of the firearm. 
     While a current embodiment of a bolt assembly has been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. 
     Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.