Patent Publication Number: US-6209249-B1

Title: Bolt for firearm allowing for reduced clearance between bolt and bolt runway

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is a bolt for a bolt action rifle having front and rear bosses with a diameter slightly larger than the rest of the bolt body, thereby allowing for a tighter tolerance between the bolt and bolt runway, and improving accuracy. 
     2. Description of the Related Art 
     Bolt action rifles have existed since the later part of the nineteenth century. Although other action types have been developed, frequently offering greater speed for following shots, bolt actions remain popular for their unequalled reputation for strength and accuracy. Their widespread use has led many inventors to propose various ways to improve their overall operation and accuracy. Additionally, the reciprocating member of other action types has come to be known as a “bolt,” and some improvements to these actions is discussed below. 
     Although present bolt action rifles are highly regarded for their accuracy potential, they are not without room for improvement. Standard bolts have a uniform diameter over the entire length of their body, with the exception of the locking lugs in front and the bolt handle in the rear. The clearance between a standard bolt and the bolt runway is a compromise between accuracy, which is achieved by reducing the clearance, and smooth operation of the bolt, which is achieved by increasing the clearance to prevent foreign particles from binding the bolt. The present invention addresses both issues by providing a bolt having a front and rear boss with a slightly larger diameter than the bolt body, thereby allowing for a tighter tolerance between the bolt and bolt runway without causing the bolt to bind. 
     An early example of a rifle having a bolt is U.S. Pat. No. 36,852, issued to John C. Nye on Nov. 4, 1862, which describes a breech-loading firearm. The firearm includes a sliding bolt held in place by a hinged latch passing through both a hole in the barrel and a corresponding hole in the bolt. 
     U.S. Pat. No. 1,198,380, issued to Grant Hammond on Sep. 12, 1916, describes a breech bolt for firearms. The bolt includes top and bottom lugs in front, an ejector channel, and an extractor. A handle is located at the rear of the bolt. The bolt is operated by lifting the handle upward, and then pulling it rearward to open the breech. Pushing the bolt handle forward and then downward closes the breech. 
     At least two inventors have proposed safety improvements for bolt action rifles. U.S. Pat. No. 2,159,485, issued to Crawford C. Loomis on May 23, 1939, describes a bolt action rifle having a bolt with a cocking handle and striker connected by a spring. A blow to the cocking handle will therefore be softened before being transmitted to the striker, thereby reducing the possibility of accidental discharge. Additionally, U.S. Pat. No. 3,631,620, issued to Banri Ohira on Jan. 4, 1972, describes a bolt wherein the sear and cocking piece are not in contact when the bolt is unlocked, but are brought into contact only when the bolt is completely locked. 
     U.S. Pat. No. 3,710,492, issued to Frank B. Tirrell on Jan. 16, 1973, describes a travel guide for bolt action rifles. The guide is located behind the locking lugs, and travels in a slot parallel to the direction of bolt travel. When the bolt is locked, the locking lugs are vertical and the travel guide remains horizontal. When the bolt is unlocked, the locking lugs are horizontal and in the same plane as the guide. One locking lug travels in a slot on the left side of the rifle, and the guide travels in a slot below the ejection port. This prevents binding of the bolt when the locking lug on the right side travels across the ejection port and can not be guided by a slot. 
     In addition to bolt actions, bolts for automatic and semiautomatic rifles have been the subject of inventive efforts. For example, U.S. Pat. No. 2,941,449, issued to Frederick P. Reed on Jun. 21, 1960, describes a decelerating device for firearms with telescoping bolts. The bolt includes a nonrotatable carrier and a rotatable head. The head includes a plurality of locking lugs. The head also includes a follower protruding through a diagonal slot on the carrier. As the bolt reaches the chamber, the locking lugs pass through a recess between a plurality of cam surfaces in the decelerator at the breech end of the barrel. When the head reaches its limit of travel, the carrier is still traveling forward. The follower within the carrier&#39;s diagonal slot causes the head to rotate so that the locking lugs engage the cam surfaces within the barrel. A similar invention is described in U.K. Pat. App. No. 2,207,493, filed by Sterling Armament Company Ltd. for an invention by Frank E. Waters and published on Feb. 1, 1989. 
     At least two inventors have proposed the use of lands and grooves on the exterior surface of a bolt for a semiautomatic or automatic rifle. U.S. Pat. No. 2,425,684, issued to George William Patchett on Aug. 12, 1947, describes a bolt having helical lands on its outside surface. The helical lands force foreign particles out the slot wherein the cocking handle travels. Additionally, U.S. Pat. No. 5,551,179, issued to Daniel H. Young on Sep. 3, 1996, describes a bolt carrier for an AR-15 or M-16 rifle having an increased number of lands and grooves. Mr. Young claims that the increased number of lands results in better bolt carrier alignment and better retention of lubricant. 
     Lastly, U.S. Pat. No. 2,861,374, issued to Samuel L. Hampton on Nov. 25, 1958, describes a bolt for a slide action rifle. The bolt includes a firing pin tube and three concentric sleeves, with the central sleeve having four inwardly biased fingers with locking heads on their front ends. The innermost sleeve is attached to the forestock sleeve. Pushing the forestock sleeve forward first moves the bolt forward, chambering a cartridge, and then pushes the inner sleeve against the central sleeve, thereby pushing the fingers outward and the locking heads into a groove within the rifle&#39;s receiver, locking the bolt in the closed position until the forearm sleeve is moved rearward. 
     No invention within the knowledge of the present inventor has addressed the problem of optimizing the firing accuracy of a bolt action rifle while preventing binding by providing increased diameter bosses at the front and rear of the bolt. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a bolt for firearm allowing for reduced clearance between bolt and bolt runway solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The invention is a bolt having an increased diameter at the rear section immediately in front of the handle, and at the front section immediately behind the locking lugs, hereinafter called a boss. These bosses allow for a tight tolerance between the bolt runway and the bolt, thereby increasing accuracy. 
     A standard bolt for a bolt action rifle has a body with a uniform diameter. The rear portion of the bolt includes a handle for operating the bolt, and the front portion includes locking lugs mating with the action adjacent to the barrel, for securing the bolt in place during firing. The locking lugs on a standard rifle may number 2, 3, 4, or even 9, and the present invention will function with any of the above numbers of lugs, or any other number. A firing pin assembly passes through the center of the bolt, and is brought into contact with the trigger mechanism of the firing pin when the bolt is fully closed and locked. The bolt may also include an extractor for hooking the rim of a cartridge case to extract it from the rifle&#39;s chamber, and/or an ejector for knocking a cartridge case out of the rifle during reciprocation of the bolt. 
     The rear boss is a section of the bolt body immediately in front of the bolt handle having a diameter slightly larger than the remainder of the bolt body. The rear boss has either a uniform or eccentric diameter, which is preferably less than or equal to 0.001 inch less than the diameter of the bolt runway, resulting in a clearance of less than or equal to 0.0005 inch between the boss and the runway. In use, the rear boss secures the rear of the bolt when the bolt is pushed fully forward, but exits the action as soon as the bolt is slightly retracted. The rear boss therefore travels outside the action for most of the bolt&#39;s reciprocating motion, so that the rear portion of the action contains the smaller diameter bolt body, thereby reducing binding during bolt cycling. 
     The front boss is located directly behind the locking lugs. The front boss comprises both major diameter sections, and minor diameter sections. The major diameter sections are limited to those portions of the bolt body directly behind the locking lugs, with those portions between the locking lugs being of the minor diameter. The major diameter boss sections therefore travel within the locking lug channels during forward or backward motion of the bolt, thereby reducing binding. When the bolt is rotated to the locked position, the major diameter portions are rotated against bearing surfaces within the action, thereby securing the front of the bolt in position. The major diameter sections are preferably equivalent to the diameter of the rear boss, and are therefore less than or equal to 0.001 inch less than the diameter of the bolt runway, resulting in less than or equal to 0.0005 inch of clearance between the boss and the runway. The minor diameter is preferable equivalent to the diameter of the remainder of the bolt body. A common example of a front and rear boss major diameter is 0.7015 inch. 
     As the bolt is cycled, the handle is rotated upwards, aligning the front boss with the locking lug channels, thereby increasing the clearance between the boss and the bolt runway to reduce binding as the action cycles. Pulling the bolt rearward disengages the rear boss from the rear portion of the bolt runway, thereby increasing the clearance between the bolt and runway. This maximized clearance exists for most of the bolt&#39;s cycle, maximizing the amount of space available to any foreign particles which may have entered the action, thereby minimizing any chance of binding. As the bolt is pushed forward, the rear boss is brought into contact with the rear of the bolt runway, thereby minimizing the clearance between the rear of the bolt and the bolt runway. When the bolt handle is rotated downward, the front boss is aligned away from the locking lug channels and against the bearing surfaces, thereby minimizing the clearance between the front of the bolt and the bolt runway. This minimized clearance ensures optimum accuracy during firing. 
     The bolt&#39;s body may include flutes to enhance the appearance of the bolt, and these flutes may assist in pushing foreign particles out of the action during bolt cycling. Straight flutes, should not be used, because of their well known propensity to contribute to binding when foreign particles are present. Wavy, spiral, or herringbone pattern flutes have been found to produce satisfactory results. Unfluted bolts have also been found to work well. 
     Accordingly, it is a principal object of the invention to provide a bolt having minimum clearance between the bolt and bolt runway when in the fully closed and locked position, thereby enhancing accuracy. 
     It is another object of the invention to provide a bolt having increased clearance between the bolt and bolt runway when the bolt is unlocked and reciprocating, thereby reducing binding. 
     It is a further object of the invention to provide a bolt having front and rear bosses, with the front boss having a major diameter directly behind the locking lugs, and a minor diameter between major diameter sections, and the rear boss having a uniform major diameter. 
     Still another object of the invention is to provide a bolt having sufficient clearance during reciprocation so that foreign particles do not cause the bolt to bind. 
     It is an object of the invention to provide improved elements and arrangements thereof for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes. 
     These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an environmental, top rear perspective view of a bolt for a firearm according to the present invention, showing the bolt in the open position. 
     FIG. 2 is an environmental, top rear perspective view of a bolt for a firearm according to the present invention, showing the bolt pushed forward but not rotated downwards to lock it closed. 
     FIG. 3 is a cross sectional view along lines  3 — 3  in FIG. 2, showing the close fit between the rear boss and bolt runway. 
     FIG. 4 is a cross sectional view along the lines  4 — 4  in FIG. 2, showing the fit between the front boss and bolt runway with the bolt rotated to the unlocked position shown in FIG.  2 . 
     FIG. 5 is an environmental, top rear perspective view of a bolt for a firearm according to the present invention, showing the bolt in the fully closed position. 
     FIG. 6 is a cross sectional view along the lines  6 — 6  in FIG. 5, showing the close fit between the front boss and the bolt runway with the bolt rotated to the locked position. 
     FIG. 7 is a top rear perspective view of a bolt according to the present invention. 
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is a bolt for a bolt action rifle having front and rear bosses with increased diameters, thereby decreasing the clearance between the bolt and bolt runway without increasing bolt binding. 
     Referring to FIG. 7, a bolt  10  is illustrated. The bolt  10  includes a front portion  12 , a central portion  14 , and a rear portion  16 . The rear portion  16  includes a bolt handle  18 , which is grasped by the shooter for reciprocating the bolt  10 . Firing pin assembly  20  extends centrally through the entire length of bolt  10 , protruding from rear portion  16 . Firing pin assembly  20  includes firing pin  22 , extending through the entire length of bolt  10 , and firing pin sleeve  24 , threadedly attached to the rear portion  16  of bolt  10 . Firing pin  22  protrudes from firing pin sleeve  24 , thereby providing a visual indicator to the cocked or uncocked condition of the firing pin  22 . The front portion  12  includes locking lugs  26 . Although two locking lugs  26  are illustrated, other numbers are commonly used, and the present invention will work with any number of locking lugs  26 . One locking lug  26  includes extractor  28 . 
     The bolt  10  of the present invention includes front boss  30 , located in front portion  12  immediately behind locking lugs  26 , and rear boss  32 , located in rear portion  16 , directly in front of bolt handle  18 , and encircling the bolt  10 . Rear boss  32  has a slightly larger diameter than the central portion  14 , and this diameter is uniform around the entire circumference of the bolt  10 . The rear boss&#39; diameter is preferably a maximum of 0.001 inch less than the diameter of the bolt runway  34  (FIGS.  1 - 6 ), providing for a clearance of less than or equal to 0.0005 inch between the rear boss  32  and bolt runway  34 . The diameter of rear boss  32  will vary with the caliber and action size of the rifle  36  (FIGS.  1 - 6 ), but a suggested example diameter is 0.7015 inch. 
     The front boss  30  includes raised sections  30   a , 30   b  each located directly behind each locking lug  26 , and has a major diameter defined by the raised sections  30   a , 30   b  equal to the diameter of the rear boss  32 . Raised sections  30   a , 30   b  are axially aligned with and preferably directly behind locking lugs  26 , and are preferably equal in width to locking lugs  26 , although smaller width front boss sections may be successfully used. Between the locking lugs and front boss sections  30   a , 30   b , front portion  12  has a minor diameter equal to the diameter of the bolt&#39;s central portion  14 . Like the rear boss  32 , the major diameter of front boss  30  is preferably a maximum of 0.001 inch less than the diameter of the bolt runway  34 , thereby providing for a maximum of 0.0005 inch of clearance between the front boss  34  and bolt runway  30 . 
     It should be noted that, although the most desirable difference in diameter between the bosses  30 , 32  and bolt runway  34  is less than 0.001 inch, the inventor can successfully utilize bosses  30 , 32  being as much as 0.0015 inch less in diameter than bolt runway  34 . 
     The central portion  14  of bolt  10  may include flutes  38 , having the primary purpose of improving the appearance of rifle  36 . The flutes  38  may serve the additional purpose of pushing foreign debris out of the action. The flutes  38  should not be straight, because the propensity of straight flutes to increase binding when foreign matter is present in the action is well known. The illustrations show flutes  38  having a wavelike pattern. Spiral flutes, herringbone style flutes, and unfluted bolts have all been found to work well with the present invention. 
     FIGS. 1-6 illustrate the bolt in conjunction with a bolt action rifle  36 . The rifle includes the well-known components of a barrel  46 , stock  48 , and bolt runway  34 , with the bolt  10  being one component of bolt runway  34 . 
     In use, a bolt  10  having front boss  30  and rear boss  32  will increase the clearance between the bolt  10  and bolt runway  34  while the action is reciprocating, and decrease this clearance when the bolt is closed and the rifle  36  is ready to fire. Referring to FIG. 1, a rifle  36  is shown with bolt  10  in the fully open position, as it would be after ejecting a spent cartridge casing or before loading the chamber. In this position, rear boss  32  is outside of bolt runway  34 , so that the clearance between the bolt&#39;s center section  14  and bolt runway  34  determines the bolt&#39;s clearance. Likewise, locking lugs  26  are aligned with the locking lug channels  40 , so that the clearance between the front portion  12  of bolt  10  is determined by the minor diameter of bolt  10 . Therefore, clearance between bolt  10  and bolt runway  34  is maximized, minimizing any tendency for binding. 
     When the bolt is pushed forward into the position shown in FIG. 2, as it would be to chamber a cartridge from a magazine or ramp (not illustrated, and well-known) or after manually inserting a cartridge into the chamber (not illustrated), rear boss  32  enters bolt runway  34 , thereby reducing the clearance between bolt  10  and bolt runway  34 . FIG. 2 illustrates bolt  10  in a forward but unlocked position, with handle  18  remaining upward as in FIG.  1 . Referring briefly to FIG. 3, the position of rear boss  32  within bolt runway  34  is illustrated. There is very little clearance between rear boss  32  and bolt runway  34 , thereby preventing movement of the rear portion  16  of bolt  10  within bolt runway  34 . 
     Referring briefly to FIG. 4, the position of the front boss  30  relative to bolt runway  34  and locking lug channels  40  is illustrated when the bolt is in the position shown in FIGS. 1 and 2. Both raised sections  30   a,    30   b  of front boss  30  are adjacent to locking lug channels  40 , so that there is maximum clearance between the front portion  12  of bolt  10  and bolt runway  34 . Therefore, when the bolt is positioned as shown in FIG. 2, the rear portion  16  has been secured against side to side movement by rear boss  32 , but the front portion  12  is still positioned so that front boss  30  allows for maximum clearance between the bolt  10  and bolt runway  34 . 
     Referring to FIG. 5, the bolt is illustrated in its fully closed position, wherein handle  18  has been rotated downward from its position in FIG.  2 . Rotating the bolt handle  18  downward moves the locking lugs  26  from their horizontal position to their vertical position. The bolt is thereby firmly secured in position primarily by the locking lugs  26  positioned against lug bearing surfaces  42 , and to a lesser extent by the bolt handle  18  fitting within handle slot  44 . Referring briefly to FIG. 6, the new orientation of the front boss  30  is illustrated. As the locking lugs  26  were rotated into a vertical position, front boss  30  was also rotated to a vertical position, thereby removing it from contact with the locking lug channels  40 , and reducing the clearance between front boss  30  and bolt runway  34 . Bolt  10  is now secured against lateral play at both front portion  12  and rear portion  16 , thereby improving the accuracy of the rifle  36 . 
     The procedure is reversed when opening the bolt  10 , as would be done either to eject a spent cartridge casing, or to verify the status of the chamber. Beginning with FIGS. 5 and 6, the bolt begins with bolt handle  18  within handle slot  44 , locking lugs  26  positioned against lug bearing surfaces  42 , and front boss  30  rotated in a vertical position wherein it bears against the bolt runway  34 . Rotating bolt handle  18  upward (FIGS. 2-4) rotates the locking lugs  26  and front boss  30  into a horizontal position wherein they are aligned within locking lug channels  40 , thereby increasing the clearance between the bolt&#39;s front end  12  and the bolt runway  34 . Pulling bolt handle  18  rearward (FIG. 1) removes rear boss  32  from bolt runway  34 , thereby increasing the clearance between the rear portion  16  of bolt  10  and bolt runway  34 . The bolt  10  now has maximum clearance between itself and bolt runway  34 , preventing binding between bolt  10  and bolt runway  34 . 
     It is to be understood that the present invention is not limited to the embodiment described above, but encompasses any and all embodiments within the scope of the following claims.