US20160169645A1

US20160169645A1 - Projectile with amorphous polymer tip

Info

Publication number: US20160169645A1
Application number: US14/566,940
Authority: US
Inventors: David E. Emary; Ryan Michael Damon
Original assignee: Hornady Manufacturing Co
Current assignee: Hornady Manufacturing Co
Priority date: 2014-12-11
Filing date: 2014-12-11
Publication date: 2016-06-16

Abstract

Projectiles with amorphous polymer tips have an elongated body, the body having a forward end, the body having a rear end opposite the forward end, the body having an intermediate cylindrical portion between the rear and forward ends, the front end of the body defining a cavity, a nose element, at least a portion of which is received in the cavity, wherein the nose element is an elongated body having opposed ends, and wherein the nose element is polymer resin having a glass transition point temperature greater than or equal to 185° C. The nose element may be a polymer resin that does not have a discrete melting point. The nose element may be a polymer resin having a glass transition point temperature less than or equal to 225° C. The nose element may be a polymer resin having a molding temperature melt point greater than or equal to 330° C.

Description

FIELD OF THE INVENTION

This invention relates to firearms ammunition, and more particularly to projectiles with expanding characteristics.

BACKGROUND OF THE INVENTION

For long-distance shooting, there is a trade-off between designing for aerodynamic performance, accuracy and terminal ballistics. Projectiles that are the most aerodynamic and accurate tend to be poor terminal performers when hunting game, and projectiles that expand effectively (especially at slower speeds after having traveled a great distance) typically lack the aerodynamic performance desired for hunting game at long ranges.
Good aerodynamics, and accuracy are provided by boat-tail hollow point (BTHP) projectiles that are popular among match competitors. However, these do not humanely dispatch game animals in long-range hunting situations. Many hunting projectiles employ hollow points filled with pointed plastic tips that help to facilitate expansion and purportedly improve aerodynamics.
Other types of projectile tips have been employed, such as inserts formed of metals like aluminum or bronze (as contrasted with tips formed of the projectile's copper jacket or lead core), which either fail to effectively expand or not provide adequate aerodynamics as needed for long range hunting or target shooting. Furthermore, metal tips suffer substantial economic disadvantages compared to injection molded polymer tips. Metal tips also require machining to form a suitable shape to achieve acceptable aerodynamics, and thus add unacceptably to the cost of a tipped projectile. Other materials serving as alternatives to polymers are also prohibitively expensive. These may include ceramics and cast resins.
For decades, widespread use of polymer tip projectiles has been considered optimal and effective technology, with no notable disadvantages. Polymer tip projectiles offer the advantage of maintaining the shape of the tip in the magazine box under recoil and purportedly provide improved downrange ballistics because the points do not flatten in the magazine like exposed lead tip projectiles. Typical polymers employed are crystalline polymers such as Delrin® and nylon. These polymers have very discrete melting points of approximately 200° C. and a low glass transition point of approximately 50° C. The glass transition point is the temperature at which the polymer transitions from a hard solid material to a soft rubbery type material.
When these crystalline polymers are exposed to temperatures that are greater than or equal to their glass transition point, they begin to soften and deform. They continue to soften and deform as their temperature increases until the temperature reaches their melt point, where the polymers essentially become liquid and completely lose their shape. Because of the very low glass transition point of the crystalline polymers, coupled with their low melt points, they are unable to withstand high temperatures and anything but modest velocities in ballistic applications without losing their shape. However, the melting points of these crystalline polymers are considered ideal for injection molding, as the material flows readily into conventional molds that do not require unusual pre-heating.
It has been unexpectedly discovered that these conventional crystalline polymers are impairing long-range effectiveness of polymer tipped projectiles because they are melting and deforming because of heating associated with the supersonic airflow around the projectile. The supersonic airflow heats the projectile's crystalline polymer tip to a sufficiently elevated temperature that causes the tip to melt and deform in response to the pressure of the airflow. Because of the very low glass transition point of the currently used Delrin® and nylon polymers, and their corresponding low melting points, these plastics can only be used at low velocities without deforming and losing their shape.
This was initially discovered by measuring the speed of projectiles over long distances using Doppler radar. Doppler radar measures the projectile's velocity at all points along the projectile's path, which in target or hunting applications can be greater than or equal to 1,000 yards. This research unexpectedly revealed that the ballistic coefficient, which is calculated from the radar data, decreased steadily as the projectile travelled downrange until the velocity dropped below approximately 2,200 fps. The decrease in ballistic coefficient indicates an increase in drag for a portion of the projectile's flight. The measurements showed the ballistic coefficient was degrading after a short amount of flight time, which depended on the projectile's initial velocity and drag characteristics. This phenomenon is caused by the crystalline polymer tip melting or softening, and subsequently deforming. Instead of a pointed tip, the tip is melting and ablating in the high temperature supersonic airflow and flattening, thereby increasing its frontal area as it travels downrange and causing increased drag. Carefully controlled Doppler radar tests were done with boat tail hollow point projectiles with precisely machined noses of increasing meplat or point diameter. All projectiles were of identical shape other than their nose diameter and were all fired at the same velocity. Results show that with a .08 caliber increase in nose diameter, the ballistic coefficient of the bullet drops 6%. For a .30 caliber bullet, this is approximately a 0.025″ increase in the nose diameter.
Current designs of crystalline polymer tips suffer from the tips melting and flattening above velocities of 2,400 fps because of aerodynamic heating. The aerodynamic stagnation temperature on the point of a projectile at 2,400 fps is approximately 300° C. 2,400 fps is a rather mundane velocity by today's standards and would be associated with older cartridge designs intended for lever action rifles. Modern hunting and target rifle cartridge designs produce velocities, depending on specific cartridge and projectile weights, of approximately 2,800 to 3,200 fps. Varmint cartridge designs can produce velocities upwards of 4,000 fps. At 3,000 fps, the aerodynamic stagnation temperature on the tip of the projectile is approximately 450° C. By today's standards, the vast majority of projectile velocities would fall within the 2,800 to 3,200 fps range. In this velocity range, the peak stagnation temperature is two to two and one-half times the melting point of currently used crystalline polymers for projectile tips.
Radar testing has shown that it takes approximately 0.05 to 0.20 seconds, depending on the initial projectile velocity and the projectile's drag for enough heat transfer to take place to cause the crystalline polymer tips to begin to melt and deform. This corresponds to distances downrange of approximately 50 to 200 yards. The melting of the tips causes the tip diameter, or meplat diameter, to become larger, which increases the aerodynamic drag on the projectile. The tip deformation is manifested in the radar data as an increase in the drag coefficient of the projectile at high velocities, which is then maintained for the remainder of the projectile's drag curve.
The crystalline polymer tip distortion begins to occur at flight distances of 50-200 yards because of the time required for heat to transfer to the tip. Data shows this distortion of the tip continues for up to 500-600 yards, depending on the projectile's aerodynamic properties. Typically, small arms have used chronograph screens at the muzzle and at most two other points downrange, typically 100 and 200 yards, to measure the approximate drag characteristics of a projectile. This limited data at short ranges has masked the issue of melting crystalline polymer tipped projectiles because it is within the window of time/distance for the effect to begin to become significant and suffer from the limitations of only two data points versus hundreds obtained via Doppler radar. The use of only three chronograph screens does not provide the resolution necessary to see the problem, and uses a very large average, which further masks the problem. The challenges of measuring downrange performance at great distances (shooting through a chronograph target) have further concealed the phenomenon of crystalline polymer tip melting and deformation. This phenomenon has been hypothesized, but no definitive work has ever been done previously to establish the heat transfer rate/times that occur in order to establish that crystalline polymer tip melting and deformation has a significant effect on long range projectile performance.
The crystalline polymer tip melting effect has been further evidenced by use of thermal imaging systems that show projectiles beginning to “glow” in infrared wavelengths after flying increasing distances, showing the heating effects. Verification has further been provided by firing crystalline polymer tipped projectiles into gelatin at long ranges (600 yards), revealing polymer tips that are distorted and exhibit evidence of heating by changes in color, material properties and shape.
With the revelation of crystalline polymer tip melting provided by research and analysis, a need exists for a new and improved projectile tip that withstands the sustained high temperatures that occur over long-range projectile flight at high speeds. In this regard, the various embodiments of the present invention substantially fulfill at least most of these needs. In this respect, the projectile with amorphous polymer tip according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of providing a projectile with a tip that maintains a consistently higher ballistic coefficient/lower drag, during long-range projectile flight at high speeds than projectiles with conventional crystalline polymer tips.

SUMMARY OF THE INVENTION

The present invention provides an improved cartridge and bullet with amorphous polymer tip, and overcomes the above-mentioned disadvantages and drawbacks of the prior art. As such, the general purpose of the present invention, which will be described subsequently in greater detail, is to provide an improved projectile with amorphous polymer tip that has all the advantages of the prior art mentioned above with significantly improved long range aerodynamic drag with resulting superior long range ballistics.
To attain this, the preferred embodiment of the present invention essentially comprises the use of amorphous polymers, such as Polysulphone (PSF), Polyetherimide (PEI), and Polyphenylsulphone (PPSU), which are very high temperature, very high glass transition point and no discrete melt point polymers as the tip material for polymer tipped projectiles for both hunting and target shooting applications. The preferred embodiment of the present invention also essentially comprises an elongated body, the body having a forward end, the body having a rear end opposite the forward end, the body having an intermediate cylindrical portion between the rear and forward ends, the front end of the body defining a cavity, a nose element, at least a portion of which is received in the cavity, wherein the nose element is an elongated body having opposed ends, and wherein the nose element is polymer resin having a glass transition point temperature greater than or equal to 185° C. The nose element may be a polymer resin that does not have a discrete melting point. The nose element may be a polymer resin having a glass transition point temperature less than or equal to 225° C. The nose element may be a polymer resin having a molding temperature melt point greater than or equal to 330° C. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of a projectile according to a preferred embodiment of the invention. This is the general design and construction for a copper jacketed, lead core, polymer tipped projectile. This projectile is a .30 caliber 208 grain projectile used for long range target shooting.

FIG. 2 is a graph illustrating the results of Doppler radar tests utilizing identical projectiles with increasing nose/meplat diameters and the effect on the G1 Ballistic coefficient. Results are displayed in dimensionless bullet calibers (diameter).

FIG. 3 is a graph illustrating the drag coefficient versus Mach number, as determined from Doppler radar, for the projectile of FIG. 1 with a crystalline polymer tip of Delrin® and an amorphous polymer tip of Polyetherimide (PEI). Both projectiles were identical and fired at the same velocity, under the same atmospheric conditions, the only difference being the material the tips are made from. As can be seen from the graph, the two projectiles start with virtually identical drag coefficients, but the projectile with the Delrin® tip rapidly climbs above the drag of the projectile with the PEI tip, and maintains higher drag throughout the entire velocity range.

FIG. 4 is a graph illustrating the drag coefficient versus Mach number, as determined from Doppler radar, of a .30 caliber 180 grain projectile, commonly used as a long range hunting bullet, with a crystalline polymer tip of Delrin® and an amorphous polymer tip of Polyetherimide (PEI). Both projectiles were identical and fired at the same velocity, under the same atmospheric conditions, the only difference being the material the tips are made from. As can be seen from the graph, the two projectiles start with virtually identical drag coefficients, but the projectile with the Delrin® tip rapidly climbs above the drag of the projectile with the PEI tip, and maintains higher drag throughout the entire velocity range.

FIG. 5 is a graph illustrating the drag coefficient versus Mach number, as determined from Doppler radar, of a .30 caliber 155 grain projectile, commonly used for 1,000 yard target competition, with a crystalline polymer tip of Delrin® and an amorphous polymer tip of Polyetherimide (PEI). Both projectiles were identical and fired at the same velocity, under the same atmospheric conditions, the only difference being the material the tips are made from. As can be seen from the graph, the two projectiles start with virtually identical drag coefficients, but the projectile with the Delrin® tip rapidly climbs above the drag of the projectile with the PEI tip, and maintains higher drag throughout the entire velocity range.

The same reference numerals refer to the same parts throughout the various figures.

DESCRIPTION OF THE CURRENT EMBODIMENT

An embodiment of the projectile with amorphous plastic tip of the present invention is shown and generally designated by the reference numeral 10.
FIG. 1 illustrates the improved projectile 10 of the present invention. More particularly, the projectile is a generally cylindrical body, symmetrical in rotation about an axis 12, with a rear end 40 and a forward tip 16. The projectile has an exterior surface shaped as follows: a rear portion 18 has a tapered frustoconical “boat tail” surface; a cylindrical intermediate portion 20 continues forward from the rear portion with a straight cylindrical side wall. Continuing, a forward ogive surface portion 22 has a gentle curve toward a meplat portion 24 at the tip. The meplat is a small diameter spherical portion. The ogive has a larger radius (as taken in a plane including the bullet's axis, as illustrated) than the intermediate section's diameter (taken in section across the axis), and also a much larger radius than that of the meplat, as will be quantified below.
The projectile 10 is formed of a copper jacket 26 having a base portion 28, with side walls 30 extending forward to a rim 32 at a forward position on the ogive section, spaced apart from the meplat. The jacket closely surrounds a lead core 34 that defines a cylindrical cavity 36 in a forward face 38 of the core. The forward face is rearward of the jacket edge 32 in this particular embodiment, and the cavity is concentric with the axis 36.
The projectile tip is formed by a nose element 40 having a first shank portion 42 and a second tapered portion 44 formed as a unitary body of the same material. The shank portion is a cylindrical portion having a diameter equal to the diameter of the jacket rim, and which is closely received in the cavity of the core. The second portion has a larger diameter than the shank at its base adjacent to the shank. The base of the second portion forms a shoulder 46, and tapers to form the tip. The jacket rim tightly grips the base of the shank at the shoulder, to secure the nose into the projectile body.
The nose element is formed of suitable amorphous plastic resins, such as Polysulphone (PSF), Polyetherimide (PEI), and Polyphenylsulphone (PPSU), which exhibit high glass transition point temperatures greater than or equal to 185° C., and high molding temperature melt points, above 330° C. Specifically, PSF has a glass transition point of 185° C., and PEI and PPSU are progressively higher, and therefore even more suitable for use in the current invention, with glass transition points of 220° C. and 225° C., respectively. In comparison, the best performing crystalline polymer used in conventional nose elements is nylon 6-6, which has a glass transition point of only 50° C. With these amorphous polymers, the velocities at which tip aerodynamic heating deformation takes place for a polymer tipped projectile can be extended from 2,400 fps associated with conventional crystalline polymer tips up into the 3,100 to 3,200 fps range of velocities. Amorphous polymers are ideal to solve this problem because of their combination of a high glass transition temperature along with the absence of a discrete melt point. Amorphous polymers typically begin to melt at temperatures between 350 to 425° C., depending on the polymer and the conditions. These polymers will withstand very high temperatures compared to conventional crystalline polymers, and only soften without melting and completely losing their shape.
Up to this point, these types of high temperature amorphous polymers have not been used for small arms projectile tips because they are a considerably more expensive polymer resin, require more handling and preparation prior to molding, and require considerably more effort to mold. As a result, parts produced from these types of polymer resins are more expensive than conventional crystalline polymer projectile tips. High temperature amorphous polymers require drying prior to molding, which the currently used crystalline polymers do not. Amorphous polymers also require specially designed molds that require heated plastic runner systems to preheat the resin prior to molding. These “hot runner” systems run at temperatures of up to 200° C. The “hot runner” systems are not required to mold crystalline polymer resins.
Despite these higher temperature and more complex equipment and procedural requirements for fabrication, use of high temperature amorphous polymers is by far a superior solution to the problem of crystalline polymer projectile tips melting during long-range projectile flight at high speeds. The use of metal tips has been largely replaced by polymers because of the very high level of manufacturing difficulty and cost associated with small metal tips. In addition, metal tips cannot be formed into the shapes required for mass production of small arms projectiles without the cost becoming so high that the tip is more expensive than the rest of the projectile.

TABLE 1

Hornady ® 30 Caliber 155 Amax Velocity vs. Distance
30 155 Amax - Retained velocity

	PEI	Delrin ®
Range (yds.)	Velocity (fps)	Velocity (fps)

0	2895	2895
100	2723	2711
200	2543	2527
300	2367	2346
400	2196	2168
500	2030	1996
600	1868	1830
700	1712	1669
800	1561	1515
900	1413	1369
1000	1272	1228
Wind drift	8.8	9.3
@ 1000 yds.
(minute of
angle)
Elevation @	31.1	32.1
1000 yds.
(minute of
angle)

Table 1 shows the results of experimentation providing the retained velocity vs. distance for Hornady® 30 caliber 155 Amax bullets with different tip material compositions. Table 1 illustrates the downrange ballistic differences for the .30 caliber 155 grain projectiles used to generate the drag coefficient data in FIG. 4. Velocity distance data is taken directly from Doppler radar, and the wind drift and elevation values are calculated using the FIG. 4 Doppler radar drag data. The amorphous polymer-tipped bullet of the current invention exits the muzzle of the rifle with identical retained velocity as the conventional Delrin® polymer-tipped bullet. However, at a range of 100 yards, the amorphous polymer-tipped bullet of the current invention already shows a higher retained velocity of 12 fps relative to Delrin®. As the range increases, the retained velocity of the amorphous polymer-tipped bullet of the current invention increases compared to the retained velocity of Delrin®. At 800 yards, the amorphous polymer-tipped bullet of the current invention has a retained velocity of 46 fps compared to Delrin®. The retained velocity of the amorphous polymer-tipped bullet of the current invention continues to compare favorably to the retained velocity of the Delrin®-tipped bullet at 900 and 1,000 yards, with a difference of 44 fps.
While a current embodiment of a projectile with amorphous plastic tip has been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.
Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

1. A bullet for a centerfire cartridge comprising:

a unitary body formed of a lead alloy surrounded by a copper jacket;

the body having a forward end;

the body having a rear end opposite the forward end;

the body having an intermediate cylindrical portion between the rear and forward ends;

the front end of the body defining a cavity;

a nose element, at least a portion of which is received in the cavity

wherein the nose element is an elongated body having opposed ends; and

wherein the nose element is polymer resin having a glass transition point temperature greater than or equal to 210° C.

2. The bullet for a centerfire cartridge of claim 1 wherein the nose element is a polymer resin that does not have a discrete melting point.

3. (canceled)

4. The bullet for a centerfire cartridge of claim 1 wherein the nose element is Polyetherimide (PEI).

5. The bullet for a centerfire cartridge of claim 1 wherein the nose element is Polyphenylsulphone (PPSU).

6. The bullet for a centerfire cartridge of claim 1 wherein the nose element is a polymer resin having a glass transition point temperature less than or equal to 225° C.

7. (canceled)

8. The bullet for a centerfire cartridge of claim 1 wherein the nose element is a polymer resin having a glass transition point temperature greater than or equal to 225° C.

9. The bullet for a centerfire cartridge of claim 1 wherein the nose element is a polymer resin having a molding temperature melt point greater than or equal to 330° C.

10. The bullet for a centerfire cartridge of claim 1 wherein one end of the nose element has a pointed tip.

11. The bullet for a centerfire cartridge of claim 1 wherein one end of the nose element is tapered.

12. The bullet for a centerfire cartridge of claim 1 wherein the portion of the nose element received in the cavity is cylindrical.

13. The bullet for a centerfire cartridge of claim 1 wherein the forward end of the body has a tapered surface portion, and wherein the nose element has an external surface portion extending smoothly from the tapered surface portion.

14. The bullet for a centerfire cartridge of claim 13 wherein the tapered surface portion of the body and the external surface portion of the nose element have a common ogive radius.

15. A bullet for a centerfire cartridge comprising:

a unitary body formed of a lead alloy surrounded by a copper jacket;

the body having a forward end;

the body having a rear end opposite the forward end;

the front end of the body defining a cavity;

a resilient pointed nose element having a first portion received in the cavity and a second portion extending from the forward end of the body; and

wherein the nose element is selected from the group consisting of Polyetherimide (PEI) and Polyphenylsulphone (PPSU).

16. The bullet for a centerfire cartridge of claim 15 wherein the second portion of the nose element is tapered.

17. The bullet for a centerfire cartridge of claim 15 wherein the first portion of the nose element is cylindrical.

18. The bullet for a centerfire cartridge of claim 15 wherein the cavity is a cylindrical bore.

19. The bullet for a centerfire cartridge of claim 15 wherein the forward end of the body has a tapered surface portion, and wherein the second portion of the nose element has an external surface portion extending smoothly from the tapered surface portion.

20. The bullet for a centerfire cartridge of claim 19 wherein the tapered surface portion of the body and the external surface portion of the nose element have a common ogive radius.

21. The bullet for a centerfire cartridge of claim 1 wherein the body has a diameter of 0.3 inch.

22. The bullet for a centerfire cartridge of claim 1 wherein the body has a length greater than the nose element.

23. The bullet for a centerfire cartridge of claim 1 wherein the portion of the nose element which is received in the cavity has a cylindrical profile.

24. The bullet for a centerfire cartridge of claim 1 wherein the cavity has a smooth cylindrical profile.

25. The bullet for a centerfire cartridge of claim 1 wherein the portion of the nose element which is received in the cavity is entirely encompassed by the body.

26. The bullet for a centerfire cartridge of claim 1 wherein the nose element is polymer resin having a glass transition point temperature greater than or equal to 220° C.