WO2017197504A1

WO2017197504A1 - Self-spinning bullet and related methods of use

Info

Publication number: WO2017197504A1
Application number: PCT/CA2017/050578
Authority: WO
Inventors: Todd SCHWARK
Original assignee: Schwark Todd
Priority date: 2016-05-17
Filing date: 2017-05-15
Publication date: 2017-11-23
Also published as: US20180051967A1

Abstract

A bullet may have its base shaped such that explosive from the cartridge or chamber causes the bullet to spin. A bullet may have any shape to the base that causes spinning that closely or exactly matches the rifling of a particular rifle. The base may be structured to achieve an impellor or turbine action to angularly accelerate the bullet while the bullet is being acted upon by an axial force from a propellant explosion during free travel within the gun or while travelling along the rifling.

Description

SELF-SPINNING BULLET AND RELATED METHODS OF USE

TECHNICAL FIELD

[0001] This document relates to self-spinning or propeller bullets and related methods of use.

BACKGROUND

[0002] 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

[0003] Bullets are disclosed whose bases are shaped such that explosive from the cartridge or chamber causes the bullet to spin.

[0004] Bullets are disclosed having any shape to the base that causes spinning that closely or exactly matches the rifling of a particular rifle.

[0005] Bullets are disclosed whose base achieves an impellor or turbine action to angularly accelerate the bullet during free travel.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] A combination comprising a gun and a bullet loaded in the gun, the gun having a smoothbore barrel.

[0010] 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.

[0011] 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. [0012] 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

[0013] 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:

[0014] Fig. 1 is a perspective partial cut away view of a bullet travelling along clockwise rifling in a rifle barrel.

[0015] Fig. 2 is a partial perspective view of a base of a bullet designed for spinning within a barrel with counter-clockwise rifling.

[0016] 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.

[0017] Fig. 4 is an end view of the base of the bullet of Fig. 3.

[0018] Fig. 5 is a section view of a bullet loaded in chamber of a rifle.

[0019] Figs. 6A and 6B are side elevation views in different angular positions (ninety degrees difference) of a bullet with helical shaped vane surfaces.

[0020] 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.

[0021] Fig. 8 is a section view of a bullet loaded in a chamber of a rifle that has a smoothbore barrel.

DETAILED DESCRIPTION

[0022] Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 32A and 34A of surfaces 32 and 34,

respectively, may be defined between and separate the base 14 and the cylindrical body 12.

[0030] 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.

[0031] 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.

[0032] 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 32B, 34B, defined by leading and trailing radii, such as radii 32C, 32D 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 32C, to the trailing radii, such as radius 34D, of an angularly adjacent vane surface 34 via a radial wall 35 between radii 32C and 34D. Leading radius 34C and trailing radius 32D 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).

[0033] Referring to Figs. 3, 6A-B, and 7A-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 32C and 32D 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.

[0034] 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.

[0035] Referring to Figs. 7 A 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.

[0036] The three examples shown in Figs. 3, 6A-B, and 7A-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 32C perpendicular to the plane of the page) to a second angular position (trailing radius 32D 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.

[0037] Referring to Figs. 3, 6A-B, and 7A-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 20A 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 20A to the vane surface 32, 34.

[0038] 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.

[0039] 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 20A and surfaces 32, 34, respectively, for cases where the leading edge 20A overlaps both surfaces 32, 34. The examples all show angles 40 of ninety degrees at the positions shown.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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'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.

[0044] 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.

[0045] 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. In some cases the base 14 does not extend laterally beyond a maximum lateral width of the cylindrical body 12.

[0046] Referring to Fig. 8 the bullet 10 may be fired in a gun that has a smoothbore barrel 19. A smoothbore barrel may lack rifling grooves along a portion or the entirety of the axial length of a bullet travel portion of the interior cylindrical surface of the barrel. A smoothbore barrel 19 may have a continuous interior diameter along the axial length of the barrel, although in some cases the barrel 19 may taper or otherwise change in diameter along a part or all of the axial length. A barrel with helical grooves or polygonal rifling imparts a stabilizing gyroscopic spin to a projectile that prevents tumbling in flight and improves accuracy. Thus, rifled barrels are used in preference over smoothbore barrels. However, the shaped base 14 of the bullet 10 disclosed here imparts a torque that causes the bullet 10 to spin in a rotational direction 42 as it passes through even a smoothbore barrel 19. Thus, bullet 10 may still achieve spin, and hence improved flight stability and accuracy, despite the lack of rifling in the barrel. A smoothbore barrel 19 may improve the efficiency of force transfer to the bullet from compression of gas pressure behind bullet 10, by sizing the bullet diameter 56 and bore diameter 54 of the barrel 19 to correspond to one another, in order to reduce or eliminate the formation of axial air gaps that may otherwise form between bore wall 62 and bullet 10 adjacent rifling grooves. Smoothbore barrel 19 may be sized to reduce or eliminate friction and in some cases to reduce or eliminate direct contact, with the bullet 10, during firing relative to a rifled barrel embodiment. A rifled barrel may have a narrower inner diameter than the bullet, in order to force the bullet to contact, and rotate relative to, the rifling grooves, however, when a smoothbore barrel is used, rotation does not depend on the presence of rifling grooves, so the inner diameter of the smoothbore barrel 19 may be increased relative to a rifled barrel, thus reducing friction on the bullet and relatively increasing muzzle velocity.

[0047] 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAFMED ARE DEFINED AS FOLLOWS:

1. A bull et compri sing :

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.

2. The bullet of claim 1 in which 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.

3. The bullet of any one of claim 1 - 2 in which the base is a closed circular end of the cylindrical body.

4. The bullet of claim 3 in which 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.

5. The bullet of claim 4 in which 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.

6. The bullet of claim 5 in which the plurality of vane surfaces are angularly distributed about at least a periphery of the base.

7. The bullet of claim 6 in which a circumferential edge, defined between the base and the cylindrical body, follows the sloping of the plurality of vane surfaces.

8. The bullet of any one of claim 6 - 7 in which the plurality of vane surfaces connect radial end to radial end in a stepped fashion.

9. The bullet of any one of claim 5 - 8 in which each vane surface forms a circular sector.

10. The bullet of claim 9 in which the plurality of vane surfaces comprises two semicircular sectors.

11. The bullet of any one of claim 4 - 10 in which each vane surface is sloped with a helical shape.

12. The bullet of any one of claim 4 - 10 in which each vane surface is sloped with a planar shape.

13. The bullet of any one of claim 4 - 10 in which each vane surface is sloped with the shape of a cylindrical wall.

14. The bullet of any one of claim 1 - 13 in which the cylindrical body has a boat tail shape adjacent the base.

15. A combination comprising a gun and the bullet of any one of claim 1 - 14 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.

16. A combination comprising a gun and the bullet of any one of claim 4 - 13 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.

17. The combination of claim 16 in which each vane surface is sloped to form an angle of ninety degrees with respect to the longitudinal leading edge of the rifling path.

18. A combination comprising a gun and the bullet of any one of claim 1 - 14 loaded in the gun, the gun having a smoothbore barrel.

19. 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.

20. The method of claim 19 in which the barrel comprises a rifling path whose twist direction matches the rotational direction.

21. The method of claim 19 in which the barrel is a smoothbore barrel.