.308 Subsonic Bullet

Abstract

The invention here described of novel aerodynamics and construction has been shown to alleviate the problems inherent in subsonic ballistics, such as, but not limited to, tumbling in flight, loss of impact energy, as well as the changes in both accuracy and precision of the firearm shots fired at subsonic speeds. The subsonic bullet herein described has three main aerodynamic components that aid in subsonic flight: 1) a parabolic or hemispherical nose; 2) a cylindrical center length with parallel sides; 3) a cone-like parabolic tail with an optimized tail geometry to slowly converge the laminar flow around the bullet without introducing turbulence. These features serve to reduce air pressure and turbulent airflow around the bullet during flight.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

This invention generally relates to firearms and ammunition, and specifically to an article and method of silencing firearm shots and usage of subsonic bullets. This invention specifically relates to an exemplary embodiment of a subsonic .308 bullet, which can be utilized with standard .308 Winchester casings.

In military, hunting, or police circumstances, it is often-times desirable to silence firearm shots in order to mask the shooter's presence. One common way to achieve this is to use a sound suppressor that attaches to the end of a firearm barrel (U.S. Pat. No. 1,111,202). These dampen the sound of a firearm shot by lowering the exit pressure of the expanding gas and thereby muffling sound of the chamber explosion. However, since most ammunition used in modern firearms is supersonic (having speeds faster than 343.2 m/s or 1125 ft/s), a sonic boom is heard shortly after the bullet leaves the barrel, rendering the sound suppressor, in effect, useless, and the shooter's presence and location detectible.

In answer to this, attempts at using subsonic ammunition have been made (U.S. Pat. No. 5,822,904, U.S. Pat. No. 9,182,204). They achieve this by the use of less powder within the ammunition casing, which causes less force to be applied to the bullet during firing, and flight speeds below the speed of sound (343.2 m/s or 1125 ft/s). However, no novel design thought has been given to the bullets used in these applications, which are still designed aerodynamically for supersonic flight. When these supersonic bullets are fired at subsonic speeds, they can be prone to tumbling and energy loss, which drastically affect the accuracy and precision of the shot.

While Burkart (U.S. application Ser. No. 14/953,315) discloses some characteristics of subsonic projectiles, no disclosure is made of any specific bullet calibers or dimensions, which would provide for optimal subsonic flight. Specifically, Burkart discloses a tail angle at the juncture of the bullet tail and midsection. Any sharp angle on the surface of the bullet will create a break in laminar flow and induce turbulence, drag, and uneven pressures that will negatively affect flight stability. Applicant's invention solves the problems associated with prior subsonic bullet designs. Applicant's present invention provides subsonic bullets, which are optimized for subsonic flight. Applicant's bullet is designed with an optimized tail geometry to slowly converge the laminar flow around the bullet without introducing turbulence. Specifically, Applicant's invention provides an optimized .308 subsonic bullet, which can be utilized with a standard .308 Winchester casing.

BRIEF SUMMARY OF THE INVENTION

Two important considerations in ballistics are the projectile's flight stability and drag. Flight stability, or the projectile's ability to maintain level flight without tumbling, is a major factor in the projectile's accuracy. Meanwhile the drag force on the projectile affects its impact energy. Flight stability and drag are especially important considerations in subsonic projectiles due to the much lower rifle barrel exit velocity of the projectile. As noted above, the prior art does not disclose subsonic bullet dimensions, which provide for optimal flight stability and reduction of drag.

Using computational fluid dynamic methods, aerodynamic properties of two bullets were analyzed for flight speeds less than the speed of sound. The first bullet used was a model representative of a standard .308 bullet. The second bullet analyzed was an embodiment of Applicant's .308 subsonic bullet.

Using a polyhedral mesh with fluid properties at atmospheric conditions and a flight speed of 304.8 m/s or 1000 ft/s, values were found for the system's dynamic pressure, drag force, and pitching moment (tabulated in Table 1). The coefficient of drag was then found using the equation: CD=FDq∞A where q∞ is the free stream dynamic pressure and A is the frontal area of the bullet.

TABLE 1
Values for aerodynamic properties of inspected bullets
			Pitching
	Pressure	Drag Force	Moment	Drag
	(lbf/ft{circumflex over ( )}2)	(lbf)	(lbf-ft)	Coefficient
Standard Bullet	1163.89	0.1323	1.879E−5	0.2197
Applicant Bullet	1162.30	0.2448	−5.386E−6	0.4071

As illustrated in Table 1, the standard .308 bullet currently available had a lower drag coefficient than Applicant's design optimized for subsonic flight. This was due to the increased surface area of Applicant's design. Due to the lower drag, less energy was apparently lost due to fluid shear forces on the standard bullet's surface, thus the standard bullet exhibited slightly increased impact energy compared to Applicant's bullet.

Although the standard bullet had a better drag coefficient, it proved to be less stable in subsonic flight, with a pitching moment of 1.879E-5 lbf-ft. This meant the bullet tended to pitch nose upward and tumble at velocity less than the speed of sound. Due to its increased length and positioning of its center of mass and neutral design, Applicant's bullet tended to pitch downward, but was significantly more stable in subsonic flight. Therefore, Applicant's bullet demonstrates much improved subsonic flight characteristic compared to the standard .308 bullet, while maintaining nearly the same impact energy.

In accordance with the above principles, one embodiment of the subsonic bullet is comprised of three main aerodynamic components that aid in subsonic flight: 1) a parabolic or hemispherical nose; 2) a cylindrical center length with parallel sides; 3) a cone-like parabolic tail with optimized tail geometry to slowly converge the laminar flow around the bullet without introducing turbulence. These features serve to reduce air pressure and turbulent airflow around the bullet during flight.

In another embodiment of the subsonic bullet, the bullet is further comprised of a copper shell, and is further comprised of the tail being filled with a material having a density less than or equal to 3.0 g/cm3, and in the nose with a material having a density greater than or equal to 11 g/cm3. This puts the COM (center of mass) as far forward as possible, lending further stability to the bullet during flight.

In yet another embodiment, the subsonic bullet is proportionally longer than supersonic bullets, which allows for both an increased bullet mass and sufficient powder within the casing to establish bullet flight speeds nearing but not exceeding, the speed of sound while minimizing voids in the powder load, which reduces the chance of misfires, hangfires, and squib loads.

In yet another embodiment, specific dimensions of a .308 bullet optimized for subsonic flight are provided.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a representation of a prior art bullet.

FIG. 2 is a representation of one embodiment of the present invention.

FIG. 3 is a representation, in section, of one embodiment of the present invention.

FIG. 4 is a representation, partly in section, of a prior art bullet in use with a standard casing.

FIG. 5 is a representation, partly in section, of one embodiment of the present invention in use with a standard casing.

FIG. 6 is a computer model representation of airflow vortex, which occurs behind standard bullet during subsonic flight.

FIG. 7 is a computer model representation of pure airflow over Applicant's cone-like parabolic tail with optimized tail geometry demonstrating no vortex and optimal flight stability.

FIG. 8 is a computer model representation of the dynamic air pressure surrounding Applicant's bullet during flight.

FIG. 9 is a cross section view of Applicant's .308 bullet.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the accompanying figures, a supersonic bullet 11 of the prior art is depicted in FIG. 1, and comprises a conical into parabolic nose 1 and tapered to flat tail 2, connected by a cylindrical portion with a diameter such that it fits snugly into a casing of appropriate caliber. The aerodynamics of the prior art bullet depicted in FIG. 1 are essential for supersonic flight; the pointed nose is used to reduce air pressure against the nose of the bullet with flight speeds in excess of the speed of sound. When used in subsonic applications; however, the pointed nose and flat tail 2 cause pockets of air pressure 16 buildups that increase the drag on the bullet and reduce its impact energy as noted in table 1 above and demonstrated in FIG. 6. In addition, the position of the COM (center of mass) 3 is far enough back in the bullet to cause a loss of stability at low flight speeds; even tumbling which can have a noticeably negative impact on both accuracy and precision when fired.

With reference to FIG. 2, an embodiment of the present invention is shown. It is comprised of three aerodynamic features. The nose 4 is parabolic or hemispherical to reduce air pressure and drag at speeds below the speed of sound (343.2 m/s). For the same effect, the tail 6 is cone-like parabolic, with an optimized tail geometry to slowly converge the laminar flow around the bullet without introducing turbulence, which is depicted in FIGS. 7-8. The cylindrical midsection 5 is of equivalent diameter to that of the prior art bullet in FIG. 1, for the same standard caliber, yet is proportionally longer than the prior art bullet, allowing the barrel rifling to more readily grasp the bullet. This causes the bullet to spin about its roll axis (this case its length or axis of trajectory), and, due to the gyroscopic properties of angular momentum, fly more accurately. The forward location of the COM 7, combined with these described aerodynamic components allows for a more stable flight at subsonic speeds over longer distances and with a flatter trajectory.

FIG. 3 illustrates one embodiment, in which an outer shell 9 of copper is filled with two materials chosen for their physical properties. The tail section 10 is filled with a material with a density less than or equal to 3.0 g/cm3, such as aluminum or magnesium. The nose section 8 fills the rest of the bullet and is comprised of a material with a density greater than or equal to 11.0 g/cm3, in this case lead. These two materials lend two benefits to the invention. First, the distribution of the dense lead with the less dense aluminum or magnesium achieves the desired forward location of the COM 7. Second the usage of the soft lead with the harder aluminum or magnesium will cause deep target penetration while still expanding for sufficient damage to the target.

When firing a bullet at subsonic speeds, less powder must be used than for supersonic speeds. When this is done in standard caliber casings 13, as is common in current applications, air pockets are created within the casing. This can cause uneven burning of the powder, or if the void is between the primer 14 and the powder, delayed fire (misfire, hangfire, or squib load). When these happen, the shooter's reactions can open him or her to harm. To solve this (without using specialized casings as in U.S. Pat. No. 5,822,904), the subsonic bullet must be longer than a supersonic bullet 11 as shown in the prior art of FIG. 1 to fill more of the interior volume of a standard caliber casing 13. With reference to FIG. 4, when using the prior art bullet 11 of FIG. 1, the tail 2 of the supersonic bullet barely extends past the neck 12 of the casing 13. However, with reference to FIG. 5, it can be seen that the subsonic bullet 15, with its cone-like parabolic tail 6 and tail section 10 extends into and fills almost half of the casing 13, thus eliminating any voids in the powder. Said cone-like parabolic tail 6 and tail section 10 can be sized to provide for an exact volume of powder, with no air voids to be utilized in a cartridge loaded with a subsonic bullet 15. An added benefit of the increased length of the subsonic bullet 15 is that it allows the bullet to be heavier using the same materials. Since the flight energy of a bullet is directly proportional to the mass and square of the velocity [E=(½)mv²], the subsonic speed of the bullet drastically lowers the impact energy of the bullet, as compared to supersonic applications. With the flight speed of the bullet being limited to the speed of sound, the mass of the bullet is the only variable that effects the energy of the bullet. So, increasing the mass of the bullet linearly increases the flight and impact energy of the bullet.

With reference to FIG. 9, an embodiment of Applicant's invention comprising specific dimensions of a .308 subsonic bullet are shown. This embodiment is comprised of an outer shell 9 of copper. The tail section 10 is filled with a material with a density less than or equal to 3.0 g/cm3, in this case magnesium. The nose section 8 fills the rest of the bullet and is comprised of a material with a density greater than or equal to 11.0 g/cm3, in this case lead. The nose 4 is in the shape of a hemisphere, or is parabolic, in order to improve subsonic laminar air flow as demonstrated in FIG. 8. A hemispheric nose is defined by the equation:

r=√{square root over (x²+y²)}

Where:

• • r=radius of the bullet;
  • x=distance from center of hemisphere along central axis to the surface of the nose; and
  • y=distance from center of hemisphere perpendicular to the x axis to the surface of the nose.A parabolic nose is defined by the equation:

y=4PX

Where:

• • y=the distance from the center of the bullet to the surface of the nose;
  • P=the distance from the nose to the focal point; and
  • X=the distance from the center of the nose of the bullet to any point along the central axis of the bullet's nose.Said .308 subsonic bullet is further comprised of a cone-like parabolic tail 6 with optimized geometry to improve subsonic airflow over the tail to reduce drag and extend the effective range of the bullet as demonstrated in FIGS. 7-8. Said cone-like parabolic tail 6 geometry is defined by the equation:

$y_t=\frac{D}{0.308}*[0.01605*{\left(\frac{x}{c}\right)}^4+0.0322*{\left(\frac{x}{c}\right)}^3-0.1699*{\left(\frac{x}{c}\right)}^2-0.02335*\left(\frac{x}{c}\right)+0.154]$

Where:

• • yt=the half thickness of the tail at a given location;
  • D=the diameter of the bullet in inches;
  • C=the length of the tail in inches (approximately 50% of the total bullet length); and
  • x=the distance into the tail as measured from the point where the tail meets the cylindrical body and 0<x<c.

Applicants' .308 subsonic bullet is specifically comprised of the following specifications, as shown in FIG. 9. A subsonic bullet .308 inches in diameter. A parabolic nose 4 defined by the equation: Y=4PX. A nose section 8 comprised of a material with a density greater than or equal to 11.0 g/cm3, in this case lead. Said lead filled nose section 8 extends to 1.08 inches 20 behind the tip of the parabolic nose 4. Said nose section 8, cylindrical midsection 5 and a cone-like parabolic tail 6 are further comprised of an outer shell 9 of copper. Said outer shell 9 of copper is .03 inches thick. Said cone-like parabolic tail 6 geometry is defined by the equation:

$y_t=\frac{D}{0.308}*[0.01605*{\left(\frac{x}{c}\right)}^4+0.0322*{\left(\frac{x}{c}\right)}^3-0.1699*{\left(\frac{x}{c}\right)}^2-0.02335*\left(\frac{x}{c}\right)+0.154]$

The tail section 10 is filled with a material with a density less than or equal to 3.0 g/cm3, in this case magnesium. Where the center of mass 17 of the nose section 8 comprised of lead is located .54 inches behind the tip of said parabolic nose 4. The center of mass 18 of the outer shell 9 of copper is located .93 inches behind the tip of said parabolic nose 4. The center of mass 19 of the tail section 10 comprised of magnesium is located 1.33 inches behind the tip of said parabolic nose 4. The center of mass 7 of the .308 subsonic bullet is located .71 inches behind the tip of said parabolic nose 4. The total length of said .308 subsonic bullet is 2.08 inches The nose section 8 lead weight of said .308 subsonic bullet is .0208 lbf. The tail section 10 magnesium weight of said .308 subsonic bullet is .0012 lbf. The outer shell 9 of copper weight is .0125 lbf. The total weight of said .308 subsonic bullet is .0345 lbf (241.5 grains).

The invention here described of novel aerodynamics and construction has been shown to alleviate the problems inherent in subsonic ballistics, such as, but not limited to, tumbling in flight, loss of impact energy, as well as the changes in both accuracy and precision of the firearm shots fired at subsonic speeds. It is understood that the foregoing examples are merely illustrative of the present invention. Certain modifications of the articles and/or methods may be made and still achieve the objectives of the invention. Such modifications are contemplated as within the scope of the claimed invention.

Claims

1. A bullet for subsonic applications, comprising: a. a parabolic nose;b. a nose section comprised of a material having a density greater than or equal to 11.0 g/cm3, but less than 19.3 g/cm3;c. a cylindrical midsection;d. a cone-like parabolic tail;e. a tail section comprised of a material having a density less than or equal to 3.0 g/cm3; andf. an outer shell, wherein said outer shell is comprised of copper.

2. The bullet of claim 1, where said cylindrical midsection is of appropriate diameter to be utilized with a standard caliber casing.

3. The bullet of claim 2 where said standard caliber casing is a .308 caliber casing.

4. The bullet of claim 2 where said cone-like parabolic tail and tail section extend into the interior of said standard caliber casing.

5. The bullet of claim 1, where said nose section is comprised of lead.

6. The bullet of claim 1 where said tail section is comprised of aluminum.

7. The bullet of claim 1 where said tail section is comprised of magnesium.

8. A bullet for subsonic applications, comprising: a. a hemispheric nose;b. a nose section comprised of a material having a density greater than or equal to 11.0 g/cm3, but less than 19.3 g/cm3;c. a cylindrical midsection;d. a cone-like parabolic tail;e. a tail section comprised of a material having a density less than or equal to 3.0 g/cm3; andf. an outer shell, wherein said outer shell is comprised of copper.

9. The bullet of claim 8, where said cylindrical midsection is of appropriate diameter to be utilized with a standard caliber casing.

10. The bullet of claim 9 where said standard caliber casing is a .308 caliber casing.

11. The bullet of claim 10 where said cone-like parabolic tail and tail section extend into the interior of said standard caliber casing.

12. The bullet of claim 8, where said nose section is comprised of lead.

13. The bullet of claim 8 where said tail section is comprised of aluminum.

14. The bullet of claim 8 where said tail section is comprised of magnesium.

15. A .308 bullet optimized for subsonic applications comprising: a. a hemispheric nose defined by the equation: r=√{square root over (x2+y2)};b. a nose section comprised of a material having a density greater than or equal to 11.0 g/cm3, but less than 19.3 g/cm3;c. a cylindrical midsection that is .308 inches in diameter;d. a cone-like parabolic tail defined by the equation:

16. The bullet of claim 15 where said cylindrical midsection is of appropriate diameter to be utilized with a .308 caliber casing and where said cone-like parabolic tail and tail section extend into the interior of said .308 caliber casing.

17. The bullet of claim 15, where said nose section is comprised of lead.

18. The bullet of claim 15 where said tail section is comprised of aluminum.

19. The bullet of claim 15 where said tail section is comprised of magnesium.

20. A .308 bullet optimized for subsonic applications comprising: a. a parabolic nose defined by the equation: y2=4PX .b. a nose section comprised of a material having a density greater than or equal to 11.0 g/cm3, but less than 19.3 g/cm3;c. a cylindrical midsection that is .308 inches in diameter;d. a cone-like parabolic tail defined by the equation:

21. The bullet of claim 20 where said cylindrical midsection is of appropriate diameter to be utilized with a .308 caliber casing and where said cone-like parabolic tail and tail section extend into the interior of said .308 caliber casing.

22. The bullet of claim 20, where said nose section is comprised of lead.

23. The bullet of claim 22, where said nose section comprised of lead extends to 1.08 inches behind the tip of said parabolic nose.

24. The bullet of claim 20 where said tail section is comprised of aluminum.

25. The bullet of claim 20 where said tail section is comprised of magnesium.

26. The bullet of claim 22 where the center of mass of said nose section is located .54 inches behind the tip of said parabolic nose.

27. The bullet of claim 22 where the lead weight of said nose section is .0208 lbf.

28. The bullet of claim 20 where the center of mass of said outer shell comprised of copper is located .93 inches behind the tip of said parabolic nose.

29. The bullet of claim 28 where said outer shell of copper weight is .0125 lbf.

30. The bullet of claim 25 where the center of mass of said tail section is located 1.33 inches behind the tip of said parabolic nose.

31. The bullet of claim 30 where said tail section magnesium weight is .0012 lbf.

32. The bullet of claim 20 where the center of mass of said bullet is located .71 inches behind the tip of said parabolic nose.

33. The bullet of claim 20 where the overall length of said bullet is 2.08 inches.

34. The bullet of claim 20 where the weight of said bullet is .0345 lbf (241.5 grains).

35. A .308 bullet optimized for subsonic applications comprising: a. a parabolic nose defined by the equation: y2=4PX ;b. a nose section comprised of lead, where said nose section comprised of lead extends to 1.08 inches behind the tip of said parabolic nose, where the center of mass of said nose section is located .54 inches behind the tip of said parabolic nose, where the lead weight of said nose section is .0208 lbf.;c. a cylindrical midsection that is .308 inches in diameter, where said cylindrical midsection is of appropriate diameter to be utilized with a .308 caliber casing;d. a cone-like parabolic tail defined by the equation: