Abstract:
A rifle barrel for realigning a projectile which is propelled through the barrel by gas pressure, the barrel comprising: a bore having a bore diameter through which a projectile may travel; rifling ridges within the bore; and at least one bore expansion chamber in the bore, wherein a diameter of the at least one bore expansion chamber is greater than the bore diameter, wherein a length of the at least one expansion chamber is smaller than an overall length of the projectile and greater than a contact length of the projectile. A process for projecting a projectile from a rifle barrel, the process comprising: increasing gas pressure behind the projectile in the rifle barrel, whereby the projectile is propelled through the rifle barrel; and passing a burst of gas around the projectile, whereby the projectile is aligned coaxially in the rifle barrel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to firearms technology. In particular, the present invention concerns a rifle barrel having a bore configuration which projects a projectile in a highly accurate manner by correcting bullet runout without sacrificing muzzle velocity.  
           [0002]    Various rifle bore configurations have been disclosed in the industry. Several examples are discussed below.  
           [0003]    U.S. Pat. No. 4,527,348, incorporated herein by reference, discloses a gun barrel adapted to be connected to a receiver includes a rifled portion and a smoothbore portion. The rifled portion may have deeper than normal grooves to permit the escape of propellant gases past the bullet. The smoothbore portion includes an increased diameter expansion section, a reduced diameter compression section and an alignment section. Gases expanding past the bullet reduce the peak pressure in the gun barrel and provide a relatively low pressure adjacent to the muzzle at the time of bullet exit. The improved gun barrel affords increased bullet velocity and accuracy, and reduced felt recoil.  
           [0004]    U.S. Pat. No. 4,590,698, incorporated herein by reference, discloses an improved barrel for a firearm or cannon wherein the muzzle velocity of the projectile fired is controlled by systematically bypassing around the projectile during its travel through the barrel of the weapon a portion of gases generated upon firing of the weapon.  
           [0005]    U.S. Pat. No. 4,660,312, incorporated herein by reference, discloses a gun barrel having a rifled-bore section at the breech end thereof, the sections having a gas tight connection therebetween, the rifled-bore section comprising a first generally tubular body having a longitudinal bore and at least one spiral groove formed in the wall of the bore to a depth of a predetermined dimension, the rifled-bore section having a length corresponding substantially to the peak pressure point for the gun barrel, the smooth-bore section comprising a second generally tubular body having a longitudinal bore coaxial with the longitudinal bore of the rifled-bore section, and the longitudinal bore of the smooth-bore section having a diameter greater than the diameter of the bore of the rifled-bore section and less than the diameter of the spiral rifling groove.  
           [0006]    U.S. Pat. No. 5,841,058, incorporated herein by reference, discloses the construction and arrangement of projectile bearing surface interfaces rearward and forward of a recessed surface chamber of the projectile interface conjointly with the interfaces of bore wall areas segmented by recessed bore chambers which in conjunction effect the deployment/transport/disbursement/development/modulation and transformation of explosive propellant charges sequentially primed and activated rearward and forwardly of the projectile along the bore and in bore wall chambers captively converting high static gas pressure to expansively relieved dynamic propellant gas pressure directly at the projectile reducing firearm barrel recoil while energizing projectile movement along the bore in a closed-system of thermodynamic propellant energy for free flight purposes.  
           [0007]    When firing a bullet or projectile from a rifle bore, it is particularly important for the bullet to spiral or spin about its longitudinal axis as it leaves the muzzle. This ensures that the bullet will fly along a straight line through the air to impact its intended target. A problem arises when cartridges are loaded with a bullet wherein the bullet is misaligned relative to the casing. A casing having been loaded in this manner is said to have some degree of runout. For example, as shown in FIG. 1A, a side view of a casing  1  is shown, wherein the casing  3  and the bullet  2  are misaligned. The bullet tip  4  is off the casing longitudinal central axis  5  by a distance, called runout  6 . It is much more preferred to have no runout, i.e., the bullet tip  4  is coaxial with the casing longitudinal central axis  5  as shown in FIG. 1B.  
           [0008]    Typical, military grade ammunition will have some degree of runout for nearly every cartridge manufactured. For example, a typical 0.223 caliber cartridge will have runout of as much as 0.09 inches. Cartridges having runout will not produce an accurate shot when fired. When a cartridge is introduced into the breach of a gun, the casing  3  fits snuggly within the breach and therefore becomes coaxially aligned with the central axes of the breach and rifle bore. If the cartridge  1  has some degree of runout, the bullet  2  will be misaligned with the central axes of the breach and rifle bore when the cartridge  1  is introduced into the breach. When a cartridge with some degree of runout is fired in a rifle, the bullet  2  will travel down the rifle bore maintaining its misaligned condition as it travels. When the misaligned bullet  2  exits the muzzle of the rifle and flies through the air, the bullet  2  will spin or rotate around an axis which is different than the longitudinal central axis of the bullet  2 . In other words, the bullet  2  will wobble as it flies through the air. This wobble or misalignment in flight causes the bullet to fly off target or deviate from its intended straight line path.  
           [0009]    Since typical grade ammunition is manufactured with some degree of runout, there is a need for a rifle bore configuration which aligns the bullet as it travels down the rifle bore.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention is a rifle bore configuration that realigns a bullet as it travels from the breach to the muzzle to ensure that bullets leaving the muzzle spin perfectly without any wobble.  
           [0011]    According to one aspect of the invention, there is provided a rifle barrel for realigning a projectile which is propelled through the barrel by gas pressure, the barrel comprising: a bore having a bore diameter through which a projectile may travel; rifling ridges within the bore; and at least one bore expansion chamber in the bore, wherein a diameter of the at least one bore expansion chamber is greater than the bore diameter, wherein a length of the at least one expansion chamber is smaller than an overall length of the projectile and greater than a contact length of the projectile.  
           [0012]    According to a further aspect of the invention, there is provided a means of increasing the accuracy of the bullet by purposefully allowing gases to explode past the bullet in order to realign the bullet.  
           [0013]    According to still another aspect of the invention, there is provided a process for manufacturing a runout correction rifle barrel, the process comprising: inserting a bore cutting tool into a constant diameter rifle bore; engaging a cutter of the bore cutting tool with a bore of the rifle barrel; and moving the bore cutting tool to remove a portion of the rifle barrel from the bore.  
           [0014]    According to a further aspect of the invention, there is provided a process for projecting a projectile from a rifle barrel, the process comprising: increasing gas pressure behind the projectile in the rifle barrel, whereby the projectile is propelled through the rifle barrel; and passing a burst of gas around the projectile, whereby the projectile is aligned coaxially in the rifle barrel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The present invention is better understood by reading the following description of non-limitative embodiments with reference to the attached drawings wherein like parts in each of the several figures are identified by the same reference characters, and which are briefly described as follows.  
         [0016]    [0016]FIG. 1A is a side view of a shell having a casing and a bullet, wherein the shell was manufactured with runout.  
         [0017]    [0017]FIG. 1B is a side view of a shell having a casing and a bullet, wherein the shell was manufactured without runout.  
         [0018]    [0018]FIG. 1A is a side view of a cartridge having a casing and bullet, wherein the bullet is misaligned in the casing.  
         [0019]    [0019]FIG. 1B is a side view of a cartridge having a casing and bullet, wherein the bullet is aligned properly in the casing.  
         [0020]    [0020]FIG. 1C is a side view of a bullet.  
         [0021]    [0021]FIG. 2A is an end view of a section of a barrel of a gun, wherein the rifle bore has a bore expansion chamber.  
         [0022]    [0022]FIG. 2B is across-sectional side view of a section of a barrel of a gun having a bore expansion chamber and a bullet passing through the bore expansion chamber.  
         [0023]    [0023]FIG. 3 is a cross-sectional side view of a rifle barrel having three bore expansion chambers of the present invention.  
         [0024]    [0024]FIG. 4 is a cross-sectional end view of a section of a rifle barrel having a bore expansion chamber and four rifling ridges.  
         [0025]    [0025]FIG. 5 is a cross-sectional side view of a bore expansion chamber section of a rifle barrel and a bullet in the bore expansion chamber.  
         [0026]    [0026]FIG. 6A is a side view of a bore cutting tool for cutting a bore expansion chamber in a rifle bore.  
         [0027]    [0027]FIG. 6B is a side view of the cutting components of the cutting tool shown in FIG. 6A. 
     
    
       [0028]    It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Referring to FIGS. 2A and 2B, end and side views of an embodiment of the invention  1  are shown for a rifle barrel  7 , respectively. Reference is also made to FIGS. 4 and 5, wherein FIG. 4 is a cross-sectional end view of a bore expansion chamber  20  and FIG. 5 is a cross-sectional side view of a portion of a bore expansion chamber  20 . Rifling  10  comprises a ridge which extends from the bore  11  of the rifle barrel  7  and spirals over at least a portion of the length of the rifle barrel  7 . In the embodiment shown, there are four rifling ridges  10  which spiral down the inside of the bore  11 . The barrel  7  has a bore diameter  12  which is approximately the same or slightly less than the outside diameter of the bullet  2 . The barrel  7  also has at least one distinct bore expansion chamber  20  along its length. The bore expansion chamber  20  has a chamber diameter  21  that is greater than the bore diameter  12 . The bore expansion chamber  20  has a chamber length  22  that is less than the overall length  13  of the bullet  2 , and preferably just longer than the bullet contact length  14  (see FIG. 1C). The bore expansion chamber  20  functions to allow a short pulse of gases to explode past the bullet  2  as the bullet  2  travels through the bore expansion chamber  20 . The explosive gases passing by the bullet  2  produce relatively higher and lower pressures on the bullet tip  4 , depending on the alignment of the bullet  2  in the bore  11 . If the bullet  2  is misaligned as shown in FIG. 2B, the explosive gases passing over the top (as oriented in the figure) of the bullet tip  4  will induce more pressure on the bullet tip  4  than the explosive gases passing over the bottom of the bullet tip  4 . This unequal pressure distribution imparts a force to the bullet  2  to realign the bullet to be coaxial with the bore  11 .  
         [0030]    Referring to FIG. 3, a side view of an embodiment of the invention is shown for a gun barrel  7 . In this embodiment, the barrel  7  is a rifled bore from the breach  8  to the muzzle  9 , similar to the embodiment shown in FIGS. 2A and 2B. This embodiment has three bore expansion chambers  20  in the barrel  7 . If the bore expansion chamber  20  first encountered by the bullet (not shown) does not fully align the bullet traveling down the bore  11 , the second and third bore expansion chambers  20  will further correct the alignment. According to further embodiments of the invention any number of alignment zones are employed along the bore  7 , depending upon the particular application and severity of the runout  6  in the ammunition. In preferred embodiments of the invention, a bore expansion chamber  20  is not formed in the bore  11  too close to the breach  8  or to the muzzle  9 . The bullet  2  needs enough space between the breach  8  and the first bore expansion chamber  20  to stabilize in the bore  11  and rifling  10 . Similarly, the bullet  2  needs enough space between the last encountered bore expansion chamber  20  and the muzzle  9  for the bullet to stabilize prior to exiting the muzzle. In most rifle barrels  7 , it is preferred to provide about 6 inches of space between the breach  8  and the first bore expansion chamber  20  and between the last bore expansion chamber  20  and the muzzle  9 .  
         [0031]    Referring to FIG. 4, a cross-sectional end view, similar to FIG. 2A, of a bore expansion chamber is shown. In this embodiment of the invention, the bore  7  has four rifle ridges  10 . A dotted line shows where the surface of the bore  11  would normally be if there was not a bore expansion chamber  20 . As is known in the art, the bore diameter  12  defines the caliber of the rifle and the size of the bullets fired through the barrel  7 . The bore expansion chamber  20  has a chamber diameter  21  which is greater than the bore diameter  12 . While the chamber diameter  21  may be any size which does not compromise the integrity of the barrel  7 , it is preferred that the chamber diameter  21  be about one hundred fifteen percent (115%) the caliber or bore diameter  12 . In one embodiment of the invention, the chamber depth  23  is calculated as follows:  
         (caliber(caliber+(caliber/100)))/2=chamber depth  
         [0032]    For example, if the caliber is 0.308 inches, the chamber depth  23  is calculated as follows:  
         (0.308(0.308+(0.308/100)))/2=0.0479 inches  
         [0033]    As a further example, if the caliber is 0.223, the chamber depth  23  is calculated as follows:  
         (0.223(0.223+(0.223/100)))/2=0.0251 inches 
         [0034]    This basic formula is used to approximate the chamber depth  23  for any caliber rifle. To obtain the chamber diameter  21 , simply add two times the chamber depth  23  to the caliber or bore diameter  12 .  
         [0035]    Referring to FIG. 5, a side view of a portion of a rifle bore of the present invention is shown with a bullet  2  in a position of traveling down the rifle bore  11  in the vicinity of a bore expansion chamber  20 . The bullet  2  has a cylindrical midsection called a contact patch  15  which contacts the rifle bore  11  (see also FIG. 1C). This contacting portion of the bullet has a bullet contact length  14 . Bullets typically have a contact length  14  that is about 30% the overall length  13  of the bullet  2  and only in rare cases is the contact length  14  more than about 50% the overall length  13  of the bullet  2 . The bore expansion chamber  20  has a chamber length  22  which is related to the bullet contact length  14  according to the following expression:  
         bullet contact length+(caliber/100)=chamber length  
         [0036]    For example, if the caliber is 0.308 inches and the bullet contact length is 0.250 inches, the chamber length is calculated as follows:  
         0.250+(0.308/100)=0.2531 inches  
         [0037]    As a further example, if the caliber is 0.223 and the bullet contact length is 0.125 inches, the chamber length is calculated as follows:  
         0.125+(0.223/100)=0.1272 inches 
         [0038]    The most important aspect of designing the size and shape of the bore expansion chamber is to consider the size of the gaps between the bullet and the bore expansion chamber. Exploding gases only have the opportunity to blast past the bullet  2  for a very short period of time, when the contact patch  15  of the bullet  2  is in the middle of the bore expansion chamber  20 . In this position, a gap develops between the leading edge of the contact patch  15  and the bore expansion chamber  20  and a second gap develops between the trailing edge of the contact patch  15  and the bore expansion chamber  20 . The amount of exploding gas which passes around the bullet  2  is determined by the size of these gaps. The gaps are made larger by increasing the chamber depth  23 , the chamber length  22  or both. Further, in the embodiments of the invention illustrated in the figures, the profile of the bore expansion chamber has a smoothly sloping contour. Alternative embodiments of the invention have a stair step or squared off contour so as to increase the size of the gaps without increasing the overall chamber depth or chamber length. Embodiments that have a squared off or stair step profile tend to create a turbulent flow of the exploding gases around the bullet which is less desirable.  
         [0039]    Referring to FIG. 5, a bullet with approximately known qualities of length and diameter is propelled through the barrel. As a bullet or projectile is fired, it travels along the barrel, and makes contact with the bore  11  and the rifling ridges  10 . The projectile is pushed along the barrel  7  by the explosive gases released during firing. Until the projectile reaches a bore expansion chamber, the amount of gas that bypasses the projectile is relatively lower than what will bypass the projectile when it reaches the bore expansion chamber.  
         [0040]    The bore expansion chamber is an area of the barrel where the interior diameter of the bore is greater than the interior diameter in the adjoining narrow bore areas. Between the time the projectile passes the chamber start and the chamber end, a burst of explosive gases is allowed to bypass the projectile. This burst of gas helps to focus the path of the projectile. The bore expansion chamber does not change the rifling pattern or rifling diameter. The bore expansion chamber  20  is just longer than the length of the projectiles contact patch  15 . The chamber start is the location along the barrel where the diameter begins an increase from that of adjoining area preceding the chamber. The chamber end is the location along the barrel where the diameter narrows to that of the adjoining bore. Either the start or the end may consist of transition surfaces which depart from the adjoining narrow bore surfaces at a departure angle with discontinuities between the surfaces. In an alternate embodiment, there are no transition surfaces or discontinuities, and the chamber surface flows smoothly from the chamber start to the chamber end. The chamber surface may be generally straight, or it may form a curved surface.  
         [0041]    A rifle barrel  7  of the present invention is manufactured by modifying gun barrels having rifled bores which are widely available on the market today and known to persons of skill in the art. The rifle barrel is secured in a vise or some other mechanism to stabilize the barrel. A bore cutting tool  30 , as shown in FIGS. 6A and 6B, is then used to cut the bore expansion chamber  20 . The bore cutting tool  30  is comprised of two main components, a cutter rod  31  and an expander rod  32 . FIG. 6A is a side view of the cutter rod  31  and the expander rod  32  wherein the rods are mating. FIG. 6B is a close-up view of the cutting portion of the rods shown in FIG. 6A. The cutter rod  31  is a cylindrical rod with female threads  33  on the inside. Opposing fingers  34  are formed in the distal end of the rod, wherein the portions of the rod between the fingers  34  are removed to allow the fingers  34  to be spread in opposite directions away from each other. Each finger  34  has a notch  35  in its exterior surface. The notch  35  forms a cutting edge  36  which is what is used to cut a bore expansion chamber in a barrel. The cutter rod  31  also has a hex head  37  or some other device for gripping the rod at its proximal end. The expander rod  32  has tapered male threads  38  at its distal end and a hex head  36  or some other device for gripping the rod at its proximal end. Both the cutter rod  31  and the expander rod  32  have a lock ring  39  which is positionable on the shanks of the rods. Once a position on the shank is selected, the lock ring  39  may be locked in place on the shank of the rod. The lock rings  39  comprises any locking mechanism which is known to persons of skill in the art.  
         [0042]    The bore cutting tool  30  is used to cut a bore expansion chamber  20  in a rifled bore by inserting the cutter rod  31  into one end of the bore and inserting the expander rod  32  into the opposite end of the bore. For illustration, assume that the cutter rod  31  is inserted into the muzzle end and the expander rod  32  is inserted into the breach end. A measurement is taken to determine how far into the bore the bore expansion chamber is to be cut from the muzzle end. The lock ring  38  on the cutter rod  31  is locked in place on the shank of the cutter rod  31  so that the cutting edges  36  extend to the side of the intended bore expansion chamber  20  opposite from the muzzle  9 . The cutter rod  31  is then inserted into the muzzle end of the bore until the lock ring  39  contacts the muzzle. The expander rod  32  is then inserted into the breach end of the bore until the tapered male threads  38  engage the female threads  33  of the cutter rod  31 . The expander rod  32  is then rotated to thread into the cutter rod  31  to spread the fingers  34  apart until the cutting edges  36  contact the bore. The chamber length  22  is then calculated according to the formula above and the expander rod lock ring  39  is fixed on the shank of the expander rod at a distance from the breach  8  equal to the calculated chamber length  22 . The assembled bore cutting tool is then oscillated back and forth to allow the cutting edges  36  to cut the bore expansion chamber. The lock rings  39  are then released, moved slightly closer to the gun barrel, and reset. The expander rod  32  is then threaded slightly further into the cutter rod  31 . Again, the bore cutting tool  30  is oscillated back and forth to cut a deeper portion in the middle of the bore expansion chamber. Once this section of the bore expansion chamber is cut, the rods are removed from the bore. The cutter rod is rotated so that the fingers  34  line up with another section of the bore between the rifling ridges  10  and the cutter rod  32  is reinserted into the bore  11 . The steps of the process outlined above are then repeated until all of the sections between the rifling ridges  10  are cut at the same depth.  
         [0043]    It is preferred that the width of the cutting edge  36  is just slightly smaller than the distance between the rifling ridges  10  for the particular rifle bore being cut.  
         [0044]    In alternative embodiments of the bore cutting tool  30 , there are more than two fingers  34 . In fact, the number of fingers  34  may coincide with the number of spaces between rifling ridges for the particular rifle bore being cut. In these embodiments, the rods only need to be inserted into the bore one time to cut a bore expansion chamber.  
         [0045]    Some embodiments of the invention comprise a bore expansion chamber which does not have all of the spaces between the rifling ridges cut, but in all embodiments, the chamber should be symmetrical.  
         [0046]    While the particular embodiments for gun barrels as herein shown and disclosed in detail are fully capable of obtaining the objects and advantages hereinbefore stated, it is to be understood that they are merely illustrative of the preferred embodiments of the invention and that no limitations are intended by the details of construction or design herein shown other than as described in the appended claims.