Fast-Twist Subsonic Bullet

Abstract

A bullet designed to expand reliably at subsonic velocities has a front end region divided by notches into petals and a groove on its exterior surface. Each notch may be separated into a notch forward segment and a notch rear segment by a discontinuity. Each notch may be cut with a depth such as to provide a web of material extending along a portion of the length of a central cavity.

Claims

1. A bullet comprising: an elongated body terminating at a front end and a rear end, and symmetrically disposed about a longitudinal central axis; a cavity terminating at said front end and extending rearward therefrom along the central axis; a groove circumscribing said body at a location spaced apart from said front end; and a plurality of longitudinal notches extending generally parallel to the central axis and extending radially inwards towards said cavity, said notches each having at least one characteristic selected from the group of, having a notch forward segment extending rearward from said front end to a discontinuity, and a notch rear segment extending rearward from said discontinuity and aligned with said notch forward segment, and said notch extending inwards to a sufficient depth relative to said cavity so as to create a web extending over at least a portion of a cavity length L.sub.C of said cavity, wherein web has a web thickness T.sub.W that meets at least one criterion selected from the group of, measuring between 0.001″ and 0.100″ in thickness, measuring between 0.4% and 15% of a bullet diameter D.sub.B, measuring between 1% and 25% of a maximum petal thickness T.sub.P.

2. The bullet of claim 1 wherein said notches each have a notch forward segment extending rearward from said front end to a discontinuity, and a notch rear segment extending rearward from said discontinuity and aligned with said notch forward segment.

3. The bullet of claim 2 wherein said discontinuities of said notches are positioned such that said groove traverses said discontinuities.

4. The bullet of claim 2 wherein said discontinuity extends to an exterior surface of the bullet and disrupts said notch.

5. The bullet of claim 2 wherein said discontinuity is formed by a region of said notch having a significantly shallower depth than the depths of said notch forward segment and said notch rear segment.

6. The bullet of claim 5 wherein at least one of said notch forward segment and said notch rear segment extends to said cavity.

7. The bullet of claim 2 wherein said discontinuity is formed by a change in depth with said notch forward segment being formed by a shallower depth of cut than said notch rear segment.

8. The bullet of claim 2 wherein said notch rear segment has a rear segment average length L.sub.RS that meets at least one criterion selected from the group of, measuring at least 0.440″ in length, measuring at least 130% of the bullet diameter D.sub.B, measuring at least 370% of a maximum petal thickness T.sub.P, measuring at least 25% of a bullet overall length L.sub.B, and measuring at least 65% of the cavity length L.sub.C.

9. The bullet of claim 8 wherein said notch rear segment has a rear segment average length L.sub.RS that meets at least one criterion selected from the group of, measuring up to 0.500″ in length, measuring up to 150% of the bullet diameter D.sub.B, measuring up to 400% of a maximum petal thickness T.sub.P, measuring up to 30% of a bullet overall length L.sub.B, and measuring up to 75% of the cavity length L.sub.C.

10. The bullet of claim 2 wherein said notch rear segment has a rear segment average length L.sub.RS that meets at least one criterion selected from the group of, measuring at least 0.440″ in length, measuring at least 130% of the bullet diameter D.sub.B, measuring at least 370% of a maximum petal thickness T.sub.P, measuring at least 25% of a bullet overall length L.sub.B, and measuring at least 65% of the cavity length L.sub.C.

11. The bullet of claim 10 wherein said notch rear segment has a rear segment average length L.sub.RS that meets at least one criterion selected from the group of, measuring up to 0.500″ in length, measuring up to 150% of the bullet diameter D.sub.B, measuring up to 400% of a maximum petal thickness T.sub.P, measuring up to 30% of a bullet overall length L.sub.B, and measuring up to 75% of the cavity length L.sub.C.

12. The bullet of claim 1 wherein said notches each extend inwards to a sufficient depth relative to said cavity so as to create a web extending over at least a portion of a cavity length L.sub.C of said cavity, wherein web has a web thickness T.sub.W that meets at least one criterion selected from the group of, measuring between 0.001″ and 0.100″ in thickness, measuring between 0.4% and 15% of a bullet diameter D.sub.B, measuring between 1% and 25% of a maximum petal thickness T.sub.P.

13. The bullet of claim 12 wherein said notches each extend inwards to a sufficient depth relative to said cavity so as to create a web extending over at least a portion of a cavity length L.sub.C of said cavity, wherein web has a web thickness T.sub.W that meets at least one criterion selected from the group of, measuring between about 0.002″ and 0.050″, measuring between about 0.7% and 10% of the bullet diameter D.sub.B, measuring between 2% and 20% of the maximum petal thickness T.sub.P.

14. The bullet of claim 14 wherein said notches each extend inwards to a sufficient depth relative to said cavity so as to create a web extending over at least a portion of a cavity length L.sub.C of said cavity, wherein web has a web thickness T.sub.W that meets at least one criterion selected from the group of, measuring between about 0.003″ and 0.020″, measuring between about 0.9% and 6% of the bullet diameter D.sub.B, measuring between 2.5% and 17% of the maximum petal thickness T.sub.P.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0011] FIGS. 1-3 show bullets having a continuous ogive exterior profile and various configurations of notches that are each formed with a discontinuity between a notch forward segment and a notch rear segment.

[0012] FIGS. 4-6 show bullets having a pressure-reducing profile forward of the groove, and notch configurations respectively similar to those shown in FIGS. 1-3.

[0013] FIGS. 7-11 show further notch configurations for bullets having a pressure-reducing profile forward of the groove. FIGS. 10 & 11 show examples where the notch segments are formed by a circular cutting tool and thus are defined by arcuate ends. FIG. 11 shows some dimensions, including the average notch length L.sub.N, the average discontinuity length L.sub.D, the average notch forward segment length L.sub.FS, the average notch rear segment length L.sub.RS, and the length L.sub.B and diameter D.sub.B of the bullet.

[0014] FIGS. 12-16 show some examples of bullets having notch segments which do not extend through to the cavity, leaving a web of material between the notch and the cavity. FIGS. 12-14 show examples where neither notch segment intersects the cavity, while FIG. 15 shows an example where the notch forward segment intersects the cavity. FIG. 16 shows an example where a change in notch depth forms the discontinuity.

[0015] FIG. 17 shows an example where a notch is formed so as to leave a web of material between the notch and the cavity, but where the notch is cut with a continuous depth of cut and thus does not have a discontinuity.

DETAILED DESCRIPTION

[0016] Common elements appearing in the various bullet configurations illustrated in the partially-sectioned isometric views are as follows: [0017] bullet 100; [0018] elongated body 102; [0019] front end 104; [0020] rear end 106; [0021] central axis 108; [0022] cavity 110; [0023] groove 112; [0024] notches 114; [0025] petals 116; [0026] notch forward segment 118; [0027] discontinuity 120; and [0028] notch rear segment 122.

[0029] FIGS. 1-3 show bullets 100 having a continuous ogive exterior profile. In FIG. 1, the bullet 100 has three notches 114, each having a notch forward segment 118 and a notch rear segment 122 that are separated by a discontinuity 120. The notch 114 has an average length L.sub.N extending the length of both segments (118, 122), and divides a forward portion of the bullet 100 into three petals 116. The discontinuity 120 has a length L.sub.D (the discontinuity 118 in FIG. 1 is defined by cuts that extend perpendicular to a central axis 108). In the FIG. 1 bullet, the discontinuity 120 extends through the region of the bullet 100 having a groove 112, such that neither notch segment (118, 122) extends into the groove 112. The groove 112 has a length L.sub.G.

[0030] FIG. 2 shows a bullet 100 where each of the notch segments (118, 122) extends partway into the groove 112. The discontinuity 120 in FIG. 2 is defined by angled cuts, and has an average length L.sub.D.

[0031] FIG. 3 shows a bullet 100 where the notch rear segment 122 extends into the groove 112, but where the notch forward segment 118 does not. The discontinuity 120 extends through a portion of the groove 112.

[0032] FIGS. 4-11 show bullets 100 having a pressure-reducing profile forward of the groove. FIG. 4 shows a bullet 100 where neither notch segment (118, 122) extends into the groove 112, and the discontinuity 120 extends across the groove 112. Other than where the notch intersects the exterior surface, the notch profile is the same as that of the bullet shown in FIG. 1.

[0033] FIG. 5 shows a bullet 100 where each of the notch segments (118, 122) extends partway into the groove 112. Other than where the notch intersects the exterior surface, the notch profile is the same as that of the bullet shown in FIG. 2.

[0034] FIG. 6 shows a bullet 100 where the notch rear segment 122 extends into the groove 112, but where the notch forward segment 118 does not. The discontinuity 120 extends through a portion of the groove 112. Other than where the notch intersects the exterior surface, the notch profile is the same as that of the bullet shown in FIG. 3.

[0035] FIG. 7 shows a bullet 100 where the notch rear segment 122 extends entirely through the groove 112, and thus the discontinuity 120 is positioned forward of the groove 112.

[0036] FIG. 8 shows a bullet 100 where the notch front segment 122 extends through the groove 112, and thus the discontinuity 120 is positioned rearward of the groove 112.

[0037] FIG. 9 shows a bullet 100 where the notch has an additional notch segment 124, which divides the discontinuity 120 into a discontinuity forward segment 126 and a discontinuity rear segment 128. Alternatively, the notch could be considered as having two discontinuities and three notch segments.

[0038] FIGS. 10 & 11 show a bullet 100 where the notch segments (118, 122) are formed by a circular cutting tool (shown in FIG. 10), and thus are defined by arcuate ends. FIG. 11 shows some dimensions, including the average length L.sub.N of the notch 114, the average length L.sub.D of the discontinuity 120, the average length L.sub.FS of the notch forward segment 118, the average length L.sub.RS of the notch rear segment 122, the bullet length L.sub.B and bullet diameter D.sub.B of the bullet 100, and the cavity length L.sub.C of the cavity 110. For ease of measurement, the “average” lengths of the notch segments (L.sub.FS, L.sub.RS) may be defined by the length (measured parallel to the central axis 108) where the arc of the tool intersects a half-depth reference line 130 that is parallel to the central axis 108 and is positioned at one half the notch depth Z.sub.N.

[0039] The dimensions of the notch segments and discontinuity depend on a number of factors, which may include the particular bullet design and composition, the intended velocity and barrel twist rate, and the expected composition of the target, as well as the bullet diameter. While average lengths are illustrated, the lengths could be defined based on their interior length along the surface of the cavity 110, or externally along the exterior of the bullet 100. While three notches are illustrated, two or four notches could be employed, and could offer greater flexibility in profiles when cutting the notch segments (118, 122), as the cutting tool could pass completely through the cavity 110.

[0040] FIGS. 12-16 show some examples of bullets having notch segments which do not extend through to the cavity, and where the discontinuity may not extend to the exterior surface. The notches as illustrated are formed by a rotary cutting tool, but other tools for forming cuts or perforations could be employed. For a particular bullet design and intended twist rate, cutting to form notches having a variable profile can be used to adjust the structural integrity of the bullet along the length of the notch to obtain a desired profile of bullet strength to provide both sufficient structural integrity to resist rotational forces as well as sufficient weakness to allow reliable expansion of the petals when the bullet impacts a target. While five examples are shown, other variations could be employed. While distinct transitions between the notch segments and the discontinuity are shown, a more gradual transition could be employed, such that there is no clear demarcation of where a notch segment ends and the discontinuity begins, so long as there is an overall region of decreased notch depth that serves to provide a discontinuity that provides increased structural integrity at its location.

[0041] FIG. 12 shows a bullet 100 where a small-diameter cutting tool has been employed to form notches 114 that each have a notch forward segment 118 and a notch rear segment 122, separated by a discontinuity 120, where the cutting tool depth of cut has been limited such that the notch segments (118, 122) do not extend through to the cavity 110. The notch segments (118, 122) in FIG. 12 are formed by inserting the cutting tool to a set depth (i.e., a specified distance from the central axis 108) and moving it axially along the bullet 100 for a short distance to cut the desired segment length. Thus, except for the curved ends, the notch segments have a constant notch depth Z.sub.N. In this case, the cavity 110 has a cavity rear segment 132 with a constant diameter, so cutting the notch rear segment 122 results in a web 134 of material separating the notch 114 from the cavity 110 where the web 134 has a constant web thickness T.sub.W, extending along a portion of the cavity length L.sub.C (shown in FIG. 11). FIG. 12 also shows a maximum petal thickness T.sub.P separating the cavity rear segment 132 from the exterior surface of the bullet.

[0042] FIG. 13 shows a bullet 100 similar to that shown in FIG. 12, but where the notch segments (118, 122) are formed by inserting and withdrawing the cutting tool at several locations along the length of the bullet 100, such that the segments (118, 122) have a continually varying depth. In such cases, the average depth could be defined as the notch depth for each segment. Again, the depth of the cuts has been selected such that the notch segments (118, 122) do not extend through to the cavity 110.

[0043] FIG. 14 shows a bullet 100 similar to that shown in FIG. 13, but where the discontinuity is formed by a shallower-depth cut of the cutting tool, and thus does not extend to the exterior surface of the bullet 100. This notch 114 could be considered as quasi-continuous, as the discontinuity 120 is formed by a region of significantly-decreased notch depth rather than a complete interruption of the notch 114. As used here, a change in notch depth is considered significant if the change in depth is sufficiently great as to materially change the structural integrity of the bullet at that location. The discontinuity 120 has an average depth Z.sub.D that is significantly less than the average depth Z.sub.FS of the notch forward segment 118 and the average depth Z.sub.RS of the notch rear segment 122.

[0044] FIG. 15 shows a bullet 100 similar to that shown in FIG. 12, but where the forward notch segment 118 has been cut with sufficient depth to extend through to the cavity 110.

[0045] FIG. 16 shows a bullet 100 where a discontinuity 120 is formed by a change in notch depth between a notch rear segment 122 and a notch forward segment 118. The forward segment depth Z.sub.FS is formed by the cutting tool placed at a reduced cut depth (i.e., a greater distance from the central axis 108) than the cut depth used to form the rear segment depth Z.sub.RS. This change in cutting tool depth forms a step-like discontinuity 120 between the notch segments (118, 122). FIG. 16 also shows a rear segment average length L.sub.RS that is measured as the length between points where a mid-depth line 130 intersects the arcs of the cutting tool used to form the notch rear segment 122. At the forward end of the notch rear segment 122, the mid-depth line intersects a projection of the arcuate surface of the notch rear segment (corresponding to the position of the circular cutting tool when forming the notch rear segment 122). The cut depth results in a web 134 extending between the notch rear segment 122 and the cavity rear segment 132, as well as a forward web 136 extending between the notch forward segment 118 and a cavity forward segment 138. The segment depths (Z.sub.FS, Z.sub.RS) may be selected relative to the cavity segment diameters such that the web 134 and the forward web 136 have equal thickness. FIG. 16 also shows a petal depth Z.sub.P extending between the exterior surface of the bullet and the cavity rear segment 132.

[0046] FIG. 17 shows a bullet 100 where a notch 114 is formed by cutting at a constant notch depth Z.sub.N, so as to leave a web 134 of material between the notch 114 and the cavity 110. Because the notch is cut with a continuous depth of cut, the notch 114 in this case does not have a discontinuity. The notch rear segment average length L.sub.RS could be considered to extend to the front end 104 of the bullet 100. While the depth of cut is constant, a cavity forward segment 138 has a larger diameter than a cavity rear segment 132, and thus the notch 114 may intersect the cavity forward segment 138.

[0047] Preliminary testing of monolithic bullets made from copper alloy suggests that the rear segment average length L.sub.RS should meet at least one of the following minimum length criteria: [0048] measuring at least 0.350″ in length, [0049] measuring at least 80% of the bullet diameter D.sub.B, [0050] measuring at least 250% of a maximum petal thickness T.sub.P, [0051] measuring at least 15% of a bullet overall length L.sub.B, and [0052] measuring at least 40% of the cavity length L.sub.C.

[0053] The notch may be further configured such that the rear segment average length L.sub.RS meets at least one of the following maximum length criteria: [0054] measuring up to 1.500″ in length, [0055] measuring up to 200% of the bullet diameter D.sub.B, [0056] measuring up to 600% of a maximum petal thickness T.sub.P, [0057] measuring up to 50% of a bullet overall length L.sub.B, and [0058] measuring up to 100% of the cavity length L.sub.C.

[0059] It may be preferred for the rear segment average length L.sub.RS to meet at least one of the following minimum length criteria: [0060] measuring at least 0.400″ in length, [0061] measuring at least 100% of the bullet diameter D.sub.B, [0062] measuring at least 300% of a maximum petal thickness T.sub.P, [0063] measuring at least 20% of a bullet overall length L.sub.B, and [0064] measuring at least 50% of the cavity length L.sub.C.
The notch may be further configured such that the rear segment average length L.sub.RS meets at least one of the following preferred maximum length criteria: [0065] measuring up to 1.00″ in length, [0066] measuring up to 175% of the bullet diameter D.sub.B, [0067] measuring up to 500% of a maximum petal thickness T.sub.P, [0068] measuring up to 40% of a bullet overall length L.sub.B, and [0069] measuring up to 85% of the cavity length L.sub.C.

[0070] In general, bullets having a greater diameter (and thus exposed to greater tangential velocities for the same angular velocity) should benefit from having a relatively shorter rear segment average length L.sub.RS, while bullets having a smaller diameter should benefit from having a relatively longer rear segment average length L.sub.RS. For bullets in the range of 0.338″ diameter, it may be preferred for the rear segment average length L.sub.RS to meet at least one of the following minimum length criteria: [0071] measuring at least 0.440″ in length, [0072] measuring at least 130% of the bullet diameter D.sub.B, [0073] measuring at least 370% of a maximum petal thickness T.sub.P, [0074] measuring at least 25% of a bullet overall length L.sub.B, and [0075] measuring at least 65% of the cavity length L.sub.C.
For such bullets, it may be preferred for the rear segment average length L.sub.RS meets at least one of the following maximum length criteria: [0076] measuring up to 0.500″ in length, [0077] measuring up to 150% of the bullet diameter D.sub.B, [0078] measuring up to 400% of a maximum petal thickness T.sub.P, [0079] measuring up to 30% of a bullet overall length L.sub.B, and [0080] measuring up to 75% of the cavity length L.sub.C.

[0081] Where the notch is cut so as to provide a web of material, the web thickness T.sub.W should meet at least one of the criteria of being between about 0.4% and 15% of the bullet diameter D.sub.B, between 1% and 25% of the maximum petal thickness T.sub.P, or between about 0.001″ and 0.100″. It may be preferred for the web thickness T.sub.W to meet at least one of the criteria of being between about 0.7% and 10% of the bullet diameter D.sub.B, between 2% and 20% of the maximum petal thickness T.sub.P, or between about 0.002″ and 0.050″. In general, bullets having a greater diameter should benefit from having a relatively greater web thickness T.sub.W, while bullets having a smaller diameter should benefit from having a relatively thinner web thickness T.sub.W. For bullets in the range of 0.338″ diameter, it may be preferred for the web thickness T.sub.W to meet at least one of the criteria of being between about 0.9% and 6% of the bullet diameter D.sub.B, between 2.5% and 17% of the maximum petal thickness T.sub.P, or between about 0.003″ and 0.020″.

[0082] Several examples of 0.338″ diameter bullets with varying notch profiles were tested at velocities between about 850 and 1000 ft/s, with notch geometries and results as indicated in Table 1. Bullets employing one of the notch profiles that provided ideal expansion, penetration, and weight retention were tested on feral pigs ranging in weight from 65 to 100 lbs. and were found to be effective in killing them quickly and humanely.

TABLE-US-00001 TABLE 1 Notch profile Web T.sub.W L.sub.RS L.sub.RS/D.sub.B L.sub.RS/T.sub.P L.sub.RS/L.sub.B L.sub.RS/L.sub.C Petals only partially expanded: FIG. 12 0.010″ 0.423″ 1.25 3.52 0.244 0.638 FIG. 12 0.005″ 0.430″ 1.27 3.59 0.249 0.649 Ideal expansion, penetration, and weight retention: FIG. 16 0.010″ 0.456″ 1.35 3.80 0.264 0.688 FIG. 16 0.005″ 0.458″ 1.36 3.82 0.265 0.691 Tips of petals sheared off: FIG. 15 0.010″ 0.484″ 1.43 4.03 0.272 0.730 FIG. 16 0.010″ 0.536″ 1.58 4.46 0.310 0.808 FIG. 17 0.010″ 0.611″ 1.81 5.01 0.353 0.922 Expanded prematurely before hitting target: FIG. 15 0.005″ 0.486″ 1.44 4.05 0.281 0.733 FIG. 16 0.005″ 0.538″ 1.59 4.48 0.311 0.811 FIG. 17 0.005″ 0.610″ 1.81 5.09 0.353 .0921

[0083] Bullet designs that expand prematurely at typical subsonic velocities (roughly 750-1050 feet/sec.) may have particular utility at lower velocities (such as about 500-700 fps) for situations where especially low sound signature is desired.

[0084] While the novel features of the present invention have been described in terms of particular embodiments and preferred applications, it should be appreciated by one skilled in the art that substitution of materials and modification of details can be made without departing from the spirit of the invention.