Patent Publication Number: US-2018051967-A1

Title: Self-spinning bullet and related methods of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(e) of U.S. provisional application Ser. No. 62/337,775 filed May 17, 2016. 
    
    
     TECHNICAL FIELD 
     This document relates to self-spinning or propeller bullets and related methods of use. 
     BACKGROUND 
     Bullets are propelled by a controlled explosion through a rifled barrel of a firearm. The rifling in the barrel induces the bullet to spin to gyroscopically stabilize the bullet as it exits the muzzle end of the barrel and travels toward a target. In some cases, rifling may be configured to have a twist rate that progressively increases down the length of the barrel. 
     SUMMARY 
     Bullets are disclosed whose bases are shaped such that explosive from the cartridge or chamber causes the bullet to spin. 
     Bullets are disclosed having any shape to the base that causes spinning that closely or exactly matches the rifling of a particular rifle. 
     Bullets are disclosed whose base achieves an impellor or turbine action to angularly accelerate the bullet during free travel. 
     A bullet is disclosed comprising: a cylindrical body; a tip; and a base shaped to cause the bullet to spin, in a rotational direction about a flight axis defined by the body, on exposure to an axial force from a propellant explosion adjacent the base. 
     A combination is disclosed comprising a gun and the bullet loaded in the gun, the gun having a barrel with a rifling path defined on an interior surface of the barrel, in which the rotational direction matches a twist direction of the rifling path. 
     A combination is disclosed comprising a gun and the bullet loaded in the gun, the gun having a barrel with a rifling path defined on an interior surface of the barrel, in which the rotational direction matches a twist direction of the rifling path, and each vane surface is sloped to form an angle of ninety degrees or less, with respect to a longitudinal leading edge of the rifling path, the angle being defined moving in the rotational direction from the longitudinal edge to the vane surface. 
     A method comprising initiating a propellant explosion adjacent a base of a bullet loaded in a gun to propel the bullet down a barrel of the gun, in which the propellant explosion creates an axial force that acts upon a vane surface defined by the base of the bullet to generate a torque that causes the bullet to spin in a rotational direction about a flight axis defined by the bullet. 
     In various embodiments, there may be included any one or more of the following features: The base is shaped to cause the bullet to spin in a clockwise direction when viewing a base end of the bullet down the flight axis. The base is a closed circular end of the cylindrical body. The base defines a vane surface radially spaced from the flight axis and sloped relative to a plane defined perpendicular to the flight axis such that exposure, on the vane surface, to the axial force imparts a torque on the bullet in the rotational direction. The base defines a plurality of vane surfaces angularly distributed about the flight axis relative to one another and each being respectively sloped relative to the plane defined perpendicular to the flight axis such that exposure, on each vane surface, to the axial force imparts a torque on the bullet in the rotational direction. The plurality of vane surfaces are angularly distributed about at least a periphery of the base. A circumferential edge, defined between the base and the cylindrical body, follows the sloping of the plurality of vane surfaces. The plurality of vane surfaces connect radial end to radial end in a stepped fashion. Each vane surface forms a circular sector. The plurality of vane surfaces comprises two semi-circular sectors. Each vane surface is sloped with a helical shape. Each vane surface is sloped with a planar shape. Each vane surface is sloped with the shape of a cylindrical wall. The cylindrical body has a boat tail shape adjacent the base. Each vane surface is sloped to form an angle of ninety degrees with respect to the longitudinal leading edge of the rifling path. The barrel comprises a rifling path whose twist direction matches the rotational direction. The barrel is a smoothbore barrel. 
     These and other aspects of the device and method are set out in the claims, which are incorporated here by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which: 
         FIG. 1  is a perspective partial cut away view of a bullet travelling along clockwise rifling in a rifle barrel. 
         FIG. 2  is a partial perspective view of a base of a bullet designed for spinning within a barrel with counter-clockwise rifling. 
         FIG. 3  is a section view of a bullet made for clockwise rifling, the bullet having planar shaped vane surfaces and a boat tail base shape. 
         FIG. 4  is an end view of the base of the bullet of  FIG. 3 . 
         FIG. 5  is a section view of a bullet loaded in chamber of a rifle. 
         FIGS. 6A and 6B  are side elevation views in different angular positions (ninety degrees difference) of a bullet with helical shaped vane surfaces. 
         FIGS. 7A and 7B  are side elevation views in different angular positions (ninety degrees difference) of a bullet with vane surfaces having slopes that follow the shape of a cylindrical wall. 
     
    
    
     DETAILED DESCRIPTION 
     Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims. 
     A bullet is a projectile that is propelled toward a target by a controlled explosion within a firearm (gun). The bullet is loaded in the gun, often at the tip end of a cartridge full of gun powder, which is then ignited to propel the bullet in an axial direction. Immediately after the explosion, the bullet travels axially through the gun barrel, which may have rifling grooves to induce spin in the bullet. Rifling includes lateral projections or grooves, such as helical grooves, in the barrel of a gun to impart a spin to the bullet around its long axis. After leaving the muzzle end of the barrel, the bullet continues to travel toward a target while spinning. The resulting spin serves to gyroscopically stabilize the bullet, improving its aerodynamic stability and accuracy. 
     A rifle barrel may gradually burn out by erosion of the throat and bore caused by continual firing. Initially, the rifling in the throat may start to round off rather than have sharp corners. The rifling may gradually continue to disappear until the user can no longer contact the rifling with the loaded but unfired bullet. At some point the bore may start to heat check, evidenced by tiny shallow cracks that start to appear all over the throat area and a few inches down the barrel, sometimes having the appearance of mud flats in a dry lake bed. Once heat checking has begun, continual firing may cause small parts to pop out causing the bore to get rough and become more difficult to clean. Performance will deteriorate to greater and greater degrees throughout this process, eventually leading to a need to replace the barrel. 
     The erosion to the barrel is caused by both the extreme temperatures created by the propellant explosion, and physical contact with the bullet. Temperature and heat erosion is understood as follows. Every time a bullet is fired the propellant explosion creates a blow torch effect of powder gasses and solids that strikes the rifling. Superheated powder travels down the barrel at high speeds, weakening the barrel wall over time. 
     The effect of physical contact between the bullet and barrel is understood as follows. Every time a bullet is fired, the bullet will strike the rifling and undergo an angular acceleration over a fraction of a second from zero or nominal spin to a maximum spin rate (revolutions per length of axial travel) dependent on the dimensions of the rifling path. The actual rotation speed is dependent on the characteristics of the particular rifling and the breech velocity of the bullet among other factors. 
     The force acting on the bullet is matched by an opposing force of equal magnitude acting on the rifling, and the opposing force may gradually erode the barrel over time. A bullet may be slightly larger in diameter than the bore diameter of the corresponding barrel, or may expand (obturate) into barrel contact when fired, and as a result, a rifled barrel may impress a negative impression of itself on the sides of the bullet. The contact between the bullet and the barrel may also act to remove energy from the bullet, reducing the muzzle velocity of the bullet relative to the same bullet fired from a wider, smoothbore barrel. 
     Referring to  FIG. 1 , a bullet  10  is illustrated, having a cylindrical body  12 , a base  14 , and a tip  16 . The base  14  is shaped to cause the bullet to spin on exposure to an axial force  52  from a propellant explosion adjacent the base  14 . The effect of the explosion may thus case the bullet to spin in a rotational direction  42  about a flight axis  38  defined by the cylindrical body  12 . The rotational direction is understood to refer to a circular direction about axis  38  but for ease of understanding is drawn in the figures as a directional line  42  tangent to the part of the side wall of the bullet that is closest to the reader in the image shown. In  FIG. 1 , the rotational direction  42  is a clockwise direction when viewed along the flight axis  38  from a base end of the cylindrical body  12 , for example from below/upstream of the base. Clockwise rotation may correspond with clockwise rifling, which is most common and is shown in  FIG. 1 . Referring to  FIG. 2 , an example of a bullet  10  shaped to spin in a counter-clockwise rotational direction for use with counter-clockwise rifling is shown. 
     Referring to  FIGS. 1, 3, and 4 , examples are shown where the base  14  is or forms a closed circular end of the cylindrical body  12 . The circular shape of the base  14  may refer to the shape of the circumferential edge of the base when viewed down axis  38 , such as shown in  FIG. 4 , such that the base  14  is projected into the page. A circumferential edge, such as collectively formed by edge profiles  32 A and  34 A of surfaces  32  and  34 , respectively, may be defined between and separate the base  14  and the cylindrical body  12 . 
     Referring to  FIG. 1 , the base  14  may define one or a plurality of vane surfaces, such as surfaces  32  and  34 , each radially spaced from the flight axis  38 . Referring to  FIG. 3 , each vane surface  32 ,  34  may be sloped relative to a plane  36  defined perpendicular to the flight axis  38  such that exposure, on the vane surface  32 ,  34 , to the axial force  52  imparts a torque on the bullet in the rotational direction  42 . In the example shown the magnitude of tilt of surface  32  relative to the plane  36  is denoted by angle  44 , which may be an acute angle. 
     Referring to  FIGS. 1 and 2 , in both embodiments, vane surface  32  and  34  are angularly distributed about the flight axis  38  relative to one another and are each respectively sloped relative to the plane  36  ( FIG. 3 ) to impart a torque on the bullet in the same rotational direction  42 . Thus, each vane surface  32  and  34  converts a part of the force from axial force  52  into a rotational force that angularly accelerates the bullet  10 . Although an example is given with two inclined ramp or vane surfaces  32  and  34 , other embodiments may have one, two, three, four, ten or more such surfaces angularly distributed about the flight axis  38 . Referring to  FIG. 1 , the plurality of vane surfaces  32 ,  34  may be angularly distributed about at least a periphery of the base  14 , and in the example shown the vane surfaces  32 ,  34  collectively define the entirety of the axially-facing surfaces of the base  14 . 
     Referring to  FIGS. 1-3 , the plurality of vane surfaces  32 ,  34  may connect radial end to radial end in a stepped fashion. Referring to  FIG. 1 , each vane surface  32 ,  34  may form a respective circular sector  32 B,  34 B, defined by leading and trailing radii, such as radii  32 C,  32 D for surface  32 , from the flight axis  38 , for example semi-circular portions of the external surface area of base  14 . Circular sectors are seen when viewing the base  14  down the flight axis  38 . The vane surfaces  32 ,  34  form steps by connecting the leading radii, such as radius  32 C, to the trailing radii, such as radius  34 D, of an angularly adjacent vane surface  34  via a radial wall  35  between radii  32 C and  34 D. Leading radius  34 C and trailing radius  32 D also connect via a radial wall  35  in the same fashion. The leading radius of each vane surface may be axially closer to tip  16  than the trailing radius of angularly adjacent vane surface(s) to compress the vane structure to a relatively short axial part of the bullet  10 . A stepped base may be more balanced than a base with a single vane surface, such as single full turn helix (not shown). 
     Referring to  FIGS. 3, 6A -B, and  7 A-B, the vane surface or surfaces  32 ,  34  may have a suitable shape, several non-limiting examples of which are shown. Referring to  FIG. 3 , each vane surface  32 ,  34  may be sloped with a planar shape. A planar shape, such as the one shown, may effectively provide a varying slope angle dependent on angular position about the vane surface. In the example shown, the vane surface has a maximum slope, and hence generates a maximum potential torque, at an angular location half way between the angular end points (in this case radii  32 C and  32 D of surface  32 ) the angular length of the vane surface. Closer to the angular ends of the vane surface  32 , the slope may taper off to generate relatively less or no torque under axial force  52  at the ends. 
     Referring to  FIGS. 6A and 6B , the vane surface or surfaces  32 ,  34  may be sloped with a helical shape. A helical shape may have a consistent slope between the angular ends (radii in the semi-circularly shaped vane surface examples shown) of each vane surface. In one case, a helical shape may be a single helix with a 2π rotation, and in other cases such as the one shown the helix may be a double helix (shown), triple helix, or other plural helix formed in the stepped fashion as shown. Other suitable helical shapes may be used, for example a helicoid, and a spiral ramp. 
     Referring to  FIGS. 7A and 7B , the vane surface or vane surfaces  32 ,  34  may be sloped with a curved shape. The curved shape may be formed by cutting out, for example by machining, a vane surface, such as  32  as shown, to have the shape of a cylindrical wall, for example the inverse of a cylindrical wall as shown, of a cylinder (not shown). In the example shown the axis (not shown) of such a cylinder is perpendicular to the flight axis  38  (not shown) but laterally offset or displaced from the flight axis  38  along an axis perpendicular to both the flight axis  38  and the cylinder axis, to provide a shape that experiences a net torque on the surface  32  when exposed to the axial force  52 . The cylindrical wall may have a suitable shape such as formed by a circular, elliptical, or other type of cylinder. 
     The three examples shown in  FIGS. 3, 6A -B, and  7 A-B may be compared as follows by viewing each bullet from the side as shown, and rotating the bullet in sequence from a first angular position (leading radius  32 C perpendicular to the plane of the page) to a second angular position (trailing radius  32 D perpendicular to the plane of the page). In each example the slope is defined relative to a plane perpendicular to the flight axis  38 , with a zero slope referring to a surface parallel to the plane perpendicular to the flight axis  38 . Referring to  FIG. 3 , the slope begins at zero, climbs to a maximum positive slope defined by angle  40  half-way between angular ends, and reduces back to zero. Referring to  FIGS. 6A-B , the slope stays at a maximum slope from angular end to end. Referring to  FIGS. 7A-B , the slope begins at a slightly positive slope, builds to a maximum slope partway between angular ends, and reduces to zero slope. The stepped shape of the base  14  can also be seen in all three examples as rotating the bullet the vane surfaces rise and fall about the periphery. 
     Referring to  FIGS. 3, 6A -B, and  7 A-B, each vane surface  32 ,  34  may be sloped to form an angle  40  (or  40 ′,  40 ″ in some cases) of ninety degrees or less, with respect to a longitudinal leading edge  20 A of the rifling path  20 . As shown, the angles  40 ,  40 ′, and  40 ″ are defined moving in the rotational direction  42  from the longitudinal edge  20 A to the vane surface  32 ,  34 . 
     The slope of the vane surfaces may be adjusted, alone or in combination with adjustments to other variables such as amount and type of propellant, and barrel dimensions, in order to tailor the magnitude of angular acceleration acting on the base  14  from the propellant explosion as desired. As the angle  40  decreases, the vane surface slope may become steeper, resulting in relatively larger torque on the bullet  10 . Steeper sloping may also compensate for pressure on the sides of the boat tail section  30  of the base  14 , and for the fact that in the boat tail configuration shown the vaned part of the base has a smaller surface area for conversion of axial force to torque. In some cases, the slope or slopes are adjusted to minimize or otherwise reduce the demand on the rifling path  20  to bring the bullet  10  to a spin rate equal to the twist rate of the rifling path  20 . In cases where a non-zero free-travel clearance jump distance  46  is defined, the sloping and dimensions of the vane surfaces may be adjusted such that the bullet  10  achieves a spin rate commensurate with (for example equal to) the twist rate of the rifling path  20  prior to or on entering contact with the rifling path  20 . 
     Angles  40  greater or less than ninety degrees (acute angles) may be used, for example an angle that is within twenty percent of (plus or minus) ninety degrees. Referring to  FIGS. 6A and 7A , suffixes ′ and ″ are appended to reference character  40  to distinguish between the angle  40  between the leading edge  20 A and surfaces  32 ,  34 , respectively, for cases where the leading edge  20 A overlaps both surfaces  32 ,  34 . The examples all show angles  40  of ninety degrees at the positions shown. 
     Referring to  FIG. 5 , the bullet  10  may be loaded in a gun  47 . The gun  47  may have a barrel  18  with a rifling path  20  on an interior surface of the barrel  18  as shown. The base  14  may be shaped to rotate in the same direction as the rifling path  20 , for example if the rotational direction  42  ( FIG. 1 ) matches a twist direction of the rifling path  20 . 
     The base  14  of the bullet  10  may be initially mounted to sit within a cartridge  22  mounted in a chamber  50 , for example if the bullet  10  sits within a cartridge sleeve  28 . The cartridge  22  may contain a suitable amount and type of propellant (not shown), which may be ignited to propel and spin the bullet  10 . A primer  24  may be located adjacent a cartridge base rim  26 , the primer  24  being positioned to be struck by a hammer (not shown) connected to a trigger system to initiate the propulsive explosion of the propellant. 
     The nose or tip  16  of the bullet  10  may be seated in a mouth  48  of the gun  47 , and in some cases the mouth  48  may taper or otherwise reduce in diameter toward the barrel  18 . A free travel clearance jump distance  46 , representing the distance the bullet  10  must travel before engaging the rifling path  20 , may be defined between the cylindrical body  12  and the rifling path  20 . However, in some cases, particularly with newer barrels, the body  12  may abut the rifling groove or path  20  when the bullet  10  is loaded and ready to fire. 
     Referring to  FIG. 5 , in use, a propellant explosion is initiated to fire the bullet  10 , for example by manual actuation of a trigger (not shown) by a user. Upon initiation, a pressure wave is generated by the propellant explosion, creating an axial force  52 . Force  52  acts against the base  14  of the bullet  10  to generate a torque that causes the bullet  10  to spin in a rotational direction  42 , for example matching the twist direction of the rifling path  20  as shown, about the bullet&#39;s flight axis  38 . In some cases, the angular acceleration of the bullet  10  during free travel across distance  46  reduces wear on the rifling path  20  because the bullet  10  contacts the rifling path  20  at a non-zero angular spin rate. In some cases the propellant explosion provides a rifling assist function that cooperates with the rifling path  20  to angularly accelerate and spin the bullet  10 , reducing wear on the rifling path  20  along the rifling path. 
     Referring to  FIGS. 1 and 3 , the bullet  10  may have a suitable shape adjacent the base  14  such as a straight cylinder shape ( FIG. 1 ), or a boat tail shape ( FIG. 3 ). The number of vane surfaces  32 ,  34  may match the number of rifling paths  20  in the barrel  18 . The rifling path  20  may have a progressive or fixed twist rate along the barrel  18 . The bullet  10  may be formed by a suitable process such as creating a new bullet in the desired shape by molding, or modifying an existing bullet by machining vane surfaces into the base end of the bullet. 
     The rifling path  20  may have a suitable shape and style, such as conventional or polygonal rifling, indents, grooves, projections, or other features. The location and dimensions of the vane surfaces may be selected to balance the torque on the bullet to avoid wobble. The bullet may have a single vane surface, for example indented in an otherwise planar base end, which forms a plane perpendicular to the flight axis  38 . The tip  16  may have a suitable shape such as a closed circular end, a cone, a bicone, an ogive, or others. The base  14  may have the shape of a stepped cam disc. The vane surfaces may be arranged in a ring form about the axis  38 . The bullet  10  may be fired in a smoothbore barrel and still achieve a spin rate analogous to that attainable with rifling. A smoothbore barrel embodiment may be visualized by taking  FIG. 1  and removing the rifling grooves or paths  20 . In some cases the base  14  does not extend laterally beyond a maximum lateral width of the cylindrical body  12 . 
     In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.