Patent Application
20230392910
The present invention relates to a bullet designed to expand reliably when it impacts a target at subsonic or transonic velocities.
Expanding bullets which deform to an increased cross-section upon impact with a target are preferred in many situations, as the increased cross-section enhances the effectiveness of the bullet by increasing its ability to transfer kinetic energy to the target. However, reliable expansion has been found problematic for bullets fired at relatively low velocities, as the dynamic forces that may be employed to cause expansion are correspondingly lower. This is a particular concern for bullets designed for suppressed firearms, as the velocity of such bullets is frequently limited by the desire to avoid velocities which are sufficient to break the sound barrier, which would greatly reduce the effectiveness of suppressing the sound of the gunshot.
One attempt to provide reliable expansion of a bullet at subsonic velocities employs a bullet with slots that separate a front region of the bullet into an array of “petals”, in combination with a ram element in a cavity in the front end of the bullet, as taught in U.S. Pat. No. 9,631,910 of Lehigh Defense, LLC. In this design, the ram element is forced rearward when the bullet impacts the target, and this rearward motion acts to spread the petals apart to increase the cross-section of the bullet.
For many applications, the deficiencies of earlier bullet designs have been overcome by the bullets disclosed in U.S. Pat. No. 10,823,539, incorporated herein by reference.
While bullets such as disclosed in U.S. Pat. No. 10,823,539 have been found to provide reliable expansion, even when fired at subsonic velocities, they may lack sufficient structural integrity to withstand the rotational forces when fired from a barrel having an extremely high rifling twist rate. For example, in 0.300 Blackout, such bullets as made by Applicant have been found effective in barrels having a relatively fast 1-in-5″ twist rate, but may not have sufficient integrity when fired through a barrel having an extremely fast twist rate such as 1-in-3″ which imparts 2/3 greater rotational velocity for the same linear velocity (linear velocity typically being capped at about 1,000 ft/s to maintain the bullet subsonic for use with a sound suppressor). This is a greater concern for larger diameter rounds, as the tangential speed at the circumference of the bullet increases as its diameter increases, for the same angular velocity.
To provide reliable expansion at subsonic velocities, similar to that of the bullets disclosed in U.S. Pat. No. 10,823,539, but with greater structural integrity so as to better withstand forces imparted by high rotational speeds, bullets can be designed with notches that are configured to provide greater structural integrity in areas of the bullet where increased resistance to rotational forces is needed. Such bullets may have exterior profiles similar to those disclosed in U.S. Pat. No. 10,823,539.
A bullet can have an elongated body terminating at a front end and a rear end, and symmetrically disposed about a longitudinal central axis; the length between the front end and rear end measured along the central axis defines a bullet length LB. The bullet has an exterior maximum bullet diameter DB. A cavity terminates at the front end and extends rearward there from along the central axis, defining a cavity length LC. A groove circumscribes the body at a location spaced apart from the front end. Longitudinal notches are provided to divide a forward portion of the bullet into petals, the notches extending generally parallel to the central axis and extending inwards from the exterior surface towards the cavity, in some case, portions of the notch intersect the cavity. The groove may be configured to allow a forward portion of the petals to bend to a limited degree, facilitating expansion in a manner similar to that of the bullets disclosed in the '539 patent.
The notches may each be formed with a notch forward segment, which extends rearward from the front end to a discontinuity, and a notch rear segment, which extends rearward from the discontinuity and is aligned with the notch forward segment. The discontinuity may be located so as to extend entirely or partially through the groove, or may be forward of or rearward of the groove. The discontinuity may entirely interrupt the notch, extending to an exterior surface of the bullet (including the groove as the exterior surface), or may be formed by a region of the notch having a significantly shallower depth than that of the notch segments. The notch segments may be formed by a varying depth of cut, and in some cases a change in depth of cut may create the discontinuity. In some case, one or both of the notch segments intersects the cavity. The notch rear segment may have an average rear segment length LRS, which may be proportioned relative to other dimensions, such as bullet diameter DB, bullet length LB, cavity length LC, maximum petal thickness TP. Where the notch is formed by a circular cutting tool, the rear segment length LRS may be defined by the length along the central axis where the arc of the tool intersects a line parallel to the central axis and positioned at one half the notch depth ZN. In other cases, the rear segment length LRS could be determined by an actual average of the length of the notch rear segment extending forwards that would result (if the exterior contour of the bullet were cylindrical).
Since the exterior of the bullet typically follows a curved or curvilinear profile, the actual depth of the notches changes as the exterior contour changes, and thus “depth” of the notches or notch segments can be defined by the depth of cut required to form the notch/segment (i.e., the separation of the cutting tool from the central axis), rather than the actual depth at any particular point relative to the exterior surface of the bullet. In some cases, the cavity is segmented with a cavity front segment terminating at the front end having a greater diameter than a cavity rear segment; in such cases, the notch forward segment may intersect the cavity while the notch rear segment does not, despite having a shallower or equal depth of cut.
The notches may be formed with a depth selected to form a web of material between the notch and the cavity, extending along a portion of the cavity length LC. Where such notches are formed with a discontinuity, the depth of cut of the notch segments can be selected so as to provide a similar web thickness TW of the web of material between each notch segment and the corresponding cavity segment. The web thickness TW may be defined as a proportion of the bullet diameter DB or the maximum petal thickness TP.
Common elements appearing in the various bullet configurations illustrated in the partially-sectioned isometric views are as follows:
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.
Preliminary testing of monolithic bullets made from copper alloy suggests that the rear segment average length LRS should meet at least one of the following minimum length criteria:
The notch may be further configured such that the rear segment average length LRS meets at least one of the following maximum length criteria:
It may be preferred for the rear segment average length LRS to meet at least one of the following minimum length criteria:
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 LRS, while bullets having a smaller diameter should benefit from having a relatively longer rear segment average length LRS. For bullets in the range of 0.338″ diameter, it may be preferred for the rear segment average length LRS to meet at least one of the following minimum length criteria:
Where the notch is cut so as to provide a web of material, the web thickness TW should meet at least one of the criteria of being between about 0.4% and 15% of the bullet diameter DB, between 1% and 25% of the maximum petal thickness TP, or between about 0.001″ and 0.100″. It may be preferred for the web thickness TW to meet at least one of the criteria of being between about 0.7% and 10% of the bullet diameter DB, between 2% and 20% of the maximum petal thickness TP, or between about 0.002″ and 0.050″. In general, bullets having a greater diameter should benefit from having a relatively greater web thickness TW, while bullets having a smaller diameter should benefit from having a relatively thinner web thickness TW. For bullets in the range of 0.338″ diameter, it may be preferred for the web thickness TW to meet at least one of the criteria of being between about 0.9% and 6% of the bullet diameter DB, between 2.5% and 17% of the maximum petal thickness TP, or between about 0.003″ and 0.020″.
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.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 63349932 | Jun 2022 | US |
