Bullet with improved aerodynamics

Abstract

A bullet with a blunt meplat with reduced drag coefficient relative to a non-blunt meplat with improved speed consistency during flight shot to shot.

Claims

1. A bullet for use to form a cartridge usable in a firearm, the bullet comprising: a bullet having a nose portion, a body portion and a tail portion with the body portion having diameter of at least about 0.2 inches, the nose portion including a tip insert secured directly to a cavity in the body portion of the bullet forming the leading surface of the bullet, the tip insert constructed from a metal material that is different than the metal material constructing the bullet, the tip insert including a meplat and the nose portion increasing in diameter from the meplat toward the body portion, the meplat being a blunt surface, the blunt surface being substantially flat having a deviation from flat defined as less than or equal to 0.02 times the body portion diameter D1 and extending radially outwardly to and intersecting with an outside diameter surface of the nose portion, said meplat having a first diameter D2 and the body portion diameter D1 with the ratio of the first diameter to the second diameter being in the range of between about 0.07:1 and about 0.18:1.

2. The bullet of claim 1 wherein the ratio of the first diameter to the second diameter being in the range of between about 0.08:1 and about 0.16:1.

3. The bullet of claim 2 wherein the second diameter is in the range of between about 0.2 inches and about 0.51 inches.

4. The bullet of claim 3 wherein the metal constructing the tip insert is aluminum or aluminum alloy.

5. The bullet of claim 3 wherein the bullet is seated in a case; the case containing propellant and having a primer pocket with a seated primer.

6. The bullet of claim 3 wherein the body portion and tail portion of the bullet having a jacket formed from a first metal and a core constructed from a second metal.

7. The bullet of claim 6 wherein the tip insert includes a shoulder portion and a stem portion, the shoulder resting against the jacket metal and the stem secured within the core metal.

8. The bullet of claim 3 wherein the body portion and tail portion of the bullet being constructed from a monolithic metal.

9. The bullet of claim 3 wherein the tail portion of the bullet being a boat tail.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a longitudinal cross section view of a cartridge with a bullet;

(2) FIG. 2 is a longitudinal cross section of the bullet in FIG. 1;

(3) FIG. 3A is an enlarged fragmentary view of the bullet of FIG. 2 with a non-flat convex blunt meplat;

(4) FIG. 3B is an enlarged fragmentary view of a bullet with a non-flat concave blunt meplat;

(5) FIG. 3C is an enlarged fragmentary view of a bullet with a convex, generally conical, meplat;

(6) FIG. 3D is an enlarged fragmentary view of a bullet with a concave, generally conical, meplat;

(7) FIG. 4 is a graph showing drag coefficient as a function of Mach number for various meplat diameters for a bullet with a caliber diameter of 6.5 mm;

(8) FIG. 5 is a graph showing drag coefficient as a function of Mach number for various meplat diameters for a bullet with a caliber diameter of 7.62 mm (30 caliber);

(9) FIG. 6 is a bar chart showing shape drag standard deviation in bullet speed for various meplat diameters of a bullet with a caliber diameter of 7.62 mm (30 caliber);

(10) FIG. 7 is an isometric view of loaded cartridges in a consumer package; and

(11) FIG. 8 is an isometric view of bullets in a consumer package.

DETAILED DESCRIPTION OF THE INVENTION

(12) FIG. 1 illustrates a centerfire rifle cartridge, designated generally 11, having a case (often also called a casing) 13 with a sidewall 15 partially defining an interior chamber 17 for holding propellant 19. While a necked down case 13 is illustrated, any suitable case can be used. The illustrated case 13 includes a shoulder 21 and a neck 23. The case 13 includes a base 25 having a primer pocket 27 opening onto the bottom 29 thereof. A primer 31 is positioned within the primer pocket 27 and has the ignition end thereof exposed to the flash hole 33, which provides a primer flame a path between the primer pocket 27 and the interior 17, whereby the flame from the primer 31, when initiated by the firing pin of a firearm (not shown) striking the primer 31, passes through the flash hole 33 and ignites the propellant 19. While the primer 31 and flash hole 33 are shown as a Boxer style primer, any suitable primer arrangement can be used. A bullet 41 is seated in the neck 23 of the case 13, and is held in place at least partially by friction. A cannelure (not shown, but well known in the art) can be provided on the exterior surface of the bullet 41, in which case the free end of the neck of 23 can be crimped and extend into the cannelure, as is known in the art, for additional securement of the bullet in the case 13. Many types of cases 13 are known in the art, and include the necked down type shown, straight wall, belted, rimmed, and rimless, etc. The present invention is not limited in use to a particular type of case 13. The bullet 41 has its forward end portion (also tip or nose) 49 extending beyond the open end 50 of the neck 23, as is known in the art. The forward end portion 49 is typically tapered and may be an ogive, or generally conical and provides streamlining for a high ballistic coefficient or low drag coefficient. A circumferential inwardly extending rib (not shown) can be provided inside the jacket 51 (described below), as known in the art, to help prevent separation of the core 55 from the jacket 51 during expansion of the bullet upon impact with a target if the bullet is of an expanding type designed to “mushroom” on impact, a so-called hunting bullet. Target bullets are not designed to upset on impact. It is, however, to be understood that all bullets can upset (deform or mushroom), some on impact, depending on target hardness. It is to be understood that the bullet 41 could be used in a muzzleloader that does not use a case 13 without departing from the scope of the invention. This invention is particularly useful with centerfire rifle cartridges having a bullet diameter (D1) in the range of between about 0.2″ and about 0.51″ and a muzzle velocity (speed) in excess of about 2000 fps. The inventive bullet is also important for speed control consistency when the bullet is traveling at a speed of less than 2000 fps downrange of the muzzle.

(13) The bullet 41 is shown as a jacketed bullet. It has a jacket 51 that can be formed of a soft metal, such as a copper alloy, and can have the metal exposed on the exterior, or can be coated with a material such as molybdenum disulfide or hexagonal boron nitride (HBN). As used herein, the term “metal” can include both substantially pure metal and a metal alloy. The jacket 51 is preferably a copper alloy. The illustrated bullet 41 has a core 55 which is typically of a lead (including lead alloy) or other dense metal. A cannelure (not shown) is a groove formed in the jacket 51 and can be provided if desired. A portion of the jacket 51 defining the cannelure can extend into the core 55, locking the jacket 51 to the core 55. An inwardly extending rib (not shown) on the inside of the jacket 51 can also be provided to help lock the core 55 to the jacket 51. It is to be understood that the core 55 and jacket 51 can be a monolithic construction. In such a monolithic integral construction, the core portion and the jacket portion are made of the same material and thus homogeneous. Such a bullet is provided by Hornady and sold under the brand name GMX®. A lead alloy core jacketed bullet is the preferred embodiment of the present invention. The manufacture of jacketed and monolithic bullets and their component materials are well known in the art.

(14) The bullet 41, as seen in FIG. 2, can be divided into three portions. The tip or nose portion 49, the body portion 63, and the tail portion 65. The nose portion 49 will be contoured to provide streamlining or aerodynamic efficiency. Such a contour can be a secant ogive contour, a spire point, or other contour that provides an increasing diameter from the forward end or meplat 67 of the nose portion 49 to the body portion 63. The meplat 67 is the forward and leading end of the bullet 41 forward end of the nose portion 49 and is blunt as described herein. The meplat 67 faces the normal direction of travel of the bullet 41 along its flight trajectory. The body portion 63 will be generally cylindrical on its exterior surface, except for perhaps one or more cannelures therein. The shape of the tail portion 65 and nose portion 49 will affect the drag coefficient. The body has a diameter D1 that is also typically considered the caliber of the bullet. It is noted here that the stated caliber is not necessarily the bullet diameter. For example, a 30 caliber bullet has a diameter of 0.308″ (within manufacturing tolerances). The body portion 63 is the portion of the bullet 41 that will engage the surface defining the bore of the barrel, notably the rifling including the lands and grooves as is known in the art. The tail portion 65 of the bullet 41 can be any suitable shape, such as a boat tail or a flat bottom. In the case of a flat base, the tail portion 65 would be flat, and perhaps the transition contour between the body section 63 and the bottom wall 71. Bullets of the aforementioned types are well known in the art.

(15) In the illustrated embodiment, the bullet 41 includes a tip insert 81. The tip insert 81 can be molded or machined, and can be of a polymeric or elastomeric material. It could also be of a metal material. The side surface of the tip insert 81 can form part of the nose portion 49. The tip insert 81 includes a shoulder 83 that engages a leading end surface 85 of the jacket 51. A stem 87 of the tip 81 extends into an open end of the jacket 51 into a pocket 91 that is at least partially formed in the core 55. As shown, a portion of the pocket 91 is also present in the forward end of the jacket 51. Preferably, the stem 87 does not extend all the way to the bottom of the pocket 91, as best seen in FIG. 2. With the tip insert 81 engaging a hard target, the tip can move longitudinally into the pocket 91, preferably before engaging the forward end of the core 55. Such a construction limits the expansion of the bullet 41 upon impact. Such a bullet, as shown, is constructed to have low expansion and be used for target shooting. Other constructions can be provided for a hunting bullet version which would provide for greater expansion or mushrooming of the bullet upon target impact. Such constructions are well known in the industry. While the bullet 41 is shown as having an insert 81, it is to be understood that the bullet could also be machined to form the inventive bullet shapes and dimensions. Target bullets are not recommended for hunting because of their limited expansion. Military engagement rules prohibit use of expanding bullets.

(16) It has been surprisingly found that blunting the meplat 67 (less pointed) improves performance of the bullet 41 while being less aerodynamic (higher drag coefficient). Traditionally, it has been believed that enhanced streamlining of the bullet's forward end (more pointed) improves bullet performance. The present invention proves this belief wrong, and tests support effectiveness of this invention. In the illustrated embodiment, the meplat 67 is the forward end of the tip insert 81, however, it is to be understood that the meplat 67 could be formed as part of the forward end of the jacket 51 and the tip insert 81 could be eliminated. Having a blunt meplat 67 provides improved performance, particularly regarding consistency of bullet speed on its flight path to the target after leaving the muzzle of the firearm, with all other cartridge characteristics being the same, for example, powder type and weight, type of primer, barrel length and twist rate. By controlling the shape and size of the meplat 67, the standard deviation for bullet speed along the bullet trajectory to the target is greatly improved. It was also surprisingly found that by controlling the size of the blunt meplat 67 in a ratio to the diameter D1 of the body portion 63, bullet trajectory to the target was greatly improved; this improvement has been found to exist across a wide range of bullet diameters. Regardless of a projectile's (bullet) initial and subsequent downrange Mach values, a projectile utilizing this invention reduces the standard deviation of velocity degradation when compared to existing projectiles that do not utilize the invention. See FIG. 6 as an example.

(17) The variability in bullet speed, both at the muzzle and along its course to target, result in variable bullet drop, which affects precision and accuracy. While a sharp pointed meplat provides a lower overall drag at higher Mach numbers, it leads to a high drag variability from shot to shot, as found and improved upon by the present invention.

(18) The inventive meplat 67 provides for a blunt tip that has a small diameter D2, but is blunt, contrary to the above discussion of bullets in the “Description of the Prior Art” section above. The meplat 67 has a diameter, described in more detail below, D2 in a ratio to the diameter D1, D2:D1 of 0.07:1 to 0.18:1 (for a 22 caliber, the meplat has a diameter in the range of 0.016″ and 0.040″, and a 50 caliber bullet meplat has a diameter in the range of 0.036″ and 0.092″), and preferably 0.08:1 to 0.16:1. A benefit of the invention is that the inventive meplat does not appreciably change the drag coefficient of the same bullet with a pointed or rounded tip. It has been found that these dimensions, along with a blunt end on the bullet tip, allow for both a pointed bullet and low drag coefficient, but with a significantly improved standard deviation of drag coefficient than those with a round tip end. The drag coefficient values herein are measured using the above described radar antenna and software at standard conditions and at a bullet speed of Mach 2.5.

(19) The bullets 41 are made in a manner that the diameter D2 is consistent across a series of sampled bullets. In a preferred embodiment, bullets 41 from a production run of bullets of the same denoted caliber, e.g. 30 caliber bullets, has at least 80%, and preferably at least 90%, of a sample of at least 10 bullets and preferably at least a 50 bullet sample with a diameter D2 varying no more than 0.010 inch, and preferably no more than 0.006 inch between the sampled bullets diameters D2.

(20) Referring to FIGS. 3A and 3B, the blunt face 91 of the meplat 67 is best seen for a rounded to flat meplat. As seen in FIG. 1, the meplat is part of a tip insert 81 which facilitates manufacture of the bullet 41. Blunt, for the purposes of this application, means for a rounded face 91 that R, the radius of the meplat of the face 91 within the diameter D3 is between infinity (i.e. flat) and 0.2 times the diameter D when the meplat is flat to convex. The angle θ is less than or equal to 30°, and dimension X is less than or equal to 0.02 times D1. The angle θ is that angle between a line perpendicular to the axis A-A and a line tangent to face 91 at the point where D3/2 intersects face 91, as seen in FIGS. 3A and 3B. D3 is the diameter across the face 91 at the two dimensions X from the line perpendicular to the central axis A-A at the center of the meplat between a transverse plane perpendicular to the axis A-A and a line from a point at the distance D2/2 to the center axis A-A. This means that the face 91 could be slightly contoured, for example, slightly rounded, or slightly pointed and convex or concave.

(21) FIGS. 3C and 3D show a meplat 67 with a generally conical face 91. In this case, an angle θ of 300 or less will suffice to provide a blunt face 91 regardless of the dimension X.

(22) It is to be understood that while the illustrated bullet 41 is shown as having a tip insert 81, the bullet 41 could be formed with the jacket and its forward end forming the meplat 67. In a preferred embodiment, the tip insert 81 is formed of a metal material and, alternately, could be formed as a polymeric material if desired. A desirable material is aluminum (including aluminum alloys).

(23) Experiments utilizing the herein described Doppler radar testing procedure have shown that the meplat diameter affects overall drag (ballistic coefficient and drag coefficient) of the bullet. It has also been found that the shape of the meplat leading end surface is also important. The radius that is commonly utilized on a polymer tipped bullet has the same drag benefits of a small meplat diameter, such as is achieved by pointing a BTHP bullet or a lathe turned bullet utilizing a sharp point meplat. Experiments using the Doppler radar test described herein show that the shape of the meplat affects both the overall drag, and also the variability of speed shot to shot along the bullet trajectory. That is, the standard deviation of speed is surprisingly reduced by utilizing the herein described meplat, providing for greater long-range precision and accuracy. As seen in FIG. 6, standard deviation of speed using the herein described meplat is reduced. FIG. 6 represents the standard deviation of generally at least 10 shots per trial, with standard tolerances on powder weight, case, size, etc., expressed as a percentage of the overall drag. As seen, a radiused tip shape results in more drag variability when compared to the inventive meplat described herein. Tests were conducted at an outdoor range over a 2,400 yard distance using the herein described drag coefficient test method.

(24) FIG. 7 shows a consumer package 111 of cartridges 11 as described above. The package includes an outer container 113, which is typically a paperboard box having at least one closure flap 115 that can be an end flap or top flap. The package 111 includes a cartridge holder/separator 117 removably positioned in the interior of the container 113 and removably contains a plurality of cartridges 11. Preferably, the package will contain at least 5, more preferably at least 10, and most preferably at least 20 cartridges 11, each with the above described meplat 67. The package 111 also includes indicia 120 on its exterior that will include one or more brand names, such as Hornady®, quantity, bullet line designation, which can be a brand name such as SST® or Interbond®, or bullet/cartridge type such as match or cartridge type and caliber such as 308 Winchester, bullet weight, and marketing information including a description of the meplat and its advantages.

(25) FIG. 8 shows a consumer package 131 of bullets 41 as described above. The package 131 includes an outer container 133, which is typically a paperboard box having at least one closure flap 135 that can be an end flap or top flap. The package 131 can include an inner container, like a polymeric bag (not shown), removably positioned in the interior of the container 133 and removably containing a plurality of bullets 41. Preferably, the package will contain at least 10, more preferably at least 20, and most preferably at least 50 bullets each, with the above described meplat 67. The package 131 also includes indicia 140 on its exterior that will include one or more brand names such as Hornady®, quantity, bullet line designation, which can be a brand name such as SST® or Interbond®, or bullet type such as match or cartridge type and caliber such as 30 caliber/308, bullet weight, marketing information, and a description of the meplat and its advantages.

(26) It is to be understood that marketing information can be provided separately from the packages 111 and 131 and associated with the inventive bullet 41 to provide information about the inventive bullet and its advantages over other bullets and cartridges. Such marketing information can be provided in advertising materials like magazine ads, internet material, and media, such as television and radio ads.

(27) All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains.

(28) It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention, and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein.

(29) One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary, and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.