OPTIMIZED SUBSONIC PROJECTILES
1. A subsonic ammunition cartridge comprising:
- a casing having a base end and an open end wherein said casing has an internal volume;
a primer inserted in said base end of said casing;
a projectile comprised of a nose cone, a body, and a boattail, wherein said body is disposed between said nose cone and said boattail, wherein a portion of the body section in proximity to said boattail of said projectile is inserted in the open end of said casing and press fitted to the portion of the body section;
wherein the nose cone has a first length, the body has a second length, and the boattail has a third length, wherein the third length is at least 50% as long as the first and second lengths combined.
Various embodiments of optimized subsonic projectiles are provided. For example, one exemplary subsonic projectile can include an elliptical nose cone, a cylindrical body and a boattail with various design features that can be used in a subsonic ammunition cartridge where the subsonic projectile is stabile throughout at least a segment of a flight allowing for better accuracy, maintaining low drag, maximizing range and achieving desired performance while ensuring the projectile stays below the speed of sound and lowering a noise profile of projectile and a launcher firing the projectile.
- 1. A subsonic ammunition cartridge comprising:
a casing having a base end and an open end wherein said casing has an internal volume; a primer inserted in said base end of said casing; a projectile comprised of a nose cone, a body, and a boattail, wherein said body is disposed between said nose cone and said boattail, wherein a portion of the body section in proximity to said boattail of said projectile is inserted in the open end of said casing and press fitted to the portion of the body section; wherein the nose cone has a first length, the body has a second length, and the boattail has a third length, wherein the third length is at least 50% as long as the first and second lengths combined.
- 2. A subsonic ammunition projectile comprising:
a nose cone, a body, and a boattail, wherein said body is disposed between said nose cone and said boattail, wherein the nose cone has a first length, the body has a second length, and the boattail has a third length, wherein the third length is at least 50% of the first and second lengths combined.
The present application claims priority to and is a continuation of U.S. patent application Ser. No. 14/953,315, filed Nov. 28, 2015, entitled “OPTIMIZED SUBSONIC PROJECTILES AND RELATED METHODS,” which claims priority to U.S. Provisional Patent Application Ser. No. 62/150,336, filed Apr. 21, 2015, entitled “OPTIMIZED SUBSONIC PROJECTILES,” the disclosures of which is expressly incorporated by reference herein.
The invention described herein includes contributions by one or more employees of the Department of the Navy made in performance of official duties and may be manufactured, used and licensed by or for the United States Government for any governmental purpose without payment of any royalties thereon. This invention (Navy Case 200,585) is assigned to the United States Government and is available for licensing for commercial purposes. Licensing and technical inquiries may be directed to the Technology Transfer Office, Naval Surface Warfare Center Crane, email: Cran_CTO@navy.mil.
The present invention relates to aerodynamics relative to ballistic objects that are designed to lower noise, improve stability, maximizing maintaining velocity, and adjusting drag characteristics by means of various structural and material aspects as well as methods related thereto. In particular, embodiments include designs and methods associated with ammunition for firearms, and more particularly to subsonic ammunitions, that are capable of lowering a noise profile of a gun while having a consistent minimized drop over a distance the projectile travels. An alternative embodiment can also address designs and methods associated with the projectile and charge combination that facilitates a maximum sub-sonic speed at a given set of temperature ranges as force applied to the projectile can vary based on propellant temperature due to factors such as ambient temperatures.
As some background, ballistics can address four phases. A first phase can be termed “internal ballistics” which can cover behavior of the projectile from a time the projectile'"'"'s propellant is initiated until the projectile exits a barrel. A second phase can be termed “transitional ballistics” which can cover the projectile'"'"'s behavior from a time the projectile leaves the barrel'"'"'s muzzle until pressure behind the projectile equalizes. External ballistics can cover behavior of the projectile after it exits the barrel/propellant pressure equalization until immediately before impact with a target. Terminal ballistics can cover behavior of the projectile when it hits its target.
While in the transitional ballistics phase, the projectile is still being propelled forward. A maximum velocity is reached at the end of the transitional ballistic phase and the beginning of the external ballistic phase. Maximum velocity of the projectile can be a primary constraint and/or concern in determining the characteristics and profile of the projectile at subsonic speeds. Multiple physical properties influence results of each of the four ballistic phases such as, for example, mass, sectional density, and aerodynamic shape.
External ballistics can have a substantial impact when determining characteristics and profile of the projectile. A design for the external ballistic phase can be determined by modifying physical properties and structural aspects that influence a projectile. One main goal when modifying these properties can include maintaining velocity and stability of the projectile as far down range as possible.
Terminal ballistics can refer to behavior and effects of the projectile when it hits a target. In some cases, a high velocity, deeper penetration projectile with a large hole is most desired. The shape, mass, and velocity of the projectile can influence penetration, so the initial kinetic energy when a projectile arrives at the target can provide general terminal ballistic characteristics. For terminal ballistic considerations, a terminal kinetic energy of the subsonic projectile can be calculated, and different aspects of structure/material associated with subsonic attributes are balanced against terminal ballistics considerations. Additionally, penetration of the subsonic projectile and a propellant weight for subsonic ammunition can be calculated to determine if the terminal ballistics of the subsonic projectile are effective.
Exemplary designs and methods associated with this disclosure can produce designs with a consistent trajectory and consistent drop while maintaining control of a projectile as well as ensuring that the projectile stays below the speed of sound in certain ballistics phases. Some exemplary designs of subsonic ammunition can address some or all four ballistic phases: internal, transitional, external, and terminal. By creating methods and designs that address the various ballistic phases, a profile of some embodiments of the exemplary subsonic projectile can be determined which can reduce ballistic drop, balance aerodynamic effects, maintain low drag, and factor in propellant charge considerations at varying temperatures. The present disclosure includes methods to determine optimal characteristics of subsonic ammunition and presents some exemplary embodiments of such a projectile.
One problem statement for an exemplary embodiment of this disclosure or the invention can include designing a projectile that, when fired at subsonic speeds, has improved ballistic characteristic over a supersonic projectile fired at subsonic speeds. Desired performance for some embodiments of the invention can include the following: maximizing an initial velocity as the projectile leaves a barrel, minimizing a reduction of velocity as the projectile travels down range, consistent flight trajectory (e.g., minimize dispersion, maximize precision). A trade-off can be whether precision (i.e. how closely the projectile impact points are grouped together) is more important than accuracy (i.e. how close an impact point is to the aim point). This tradeoff can be determined since aim point (and therefor accuracy) could always be adjusted once the projectile trajectory has been characterized and is known by a user, but precision could not be adjusted by the user in a similar manner.
An illustrative embodiment of the present disclosure can include a subsonic ammunition cartridge assembly comprising a projectile and a casing having a base end and an open end to receive the projectile. An optimized subsonic projectile can be designed having an elliptical nose cone, a body, and boattail section. The projectile can be sized to fit within the open end of the casing and can have structural aspects, e.g., meplat, nose shape/length, body shape/length, boattail shape/length, grooves, rebated or stepped sections, tail shape/length, etc, as well as charge disposed within the casing that collectively exhibit a desired degree of stability at subsonic velocity during, e.g. an external ballistics phase, as well as addressing drop, maximizing velocity at particular stages, etc. Different materials can be used for projectile designs that provide various effects to include external and terminal ballistics phase effects. In some embodiments, desired designs should strive to produce a highest minimum pressure coefficient as possible associated with the projectile during a subsonic external ballistics phase. In some embodiments, a desired design will provide the projectile with a highest maximum subsonic velocity. Pressure coefficient can also be a function of a thickness on a projectile object (e.g., a diameter). Associated methods are also provided to include methods of designing, manufacturing, assembly, and use.
Any additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.
The detailed description of the drawings particularly refers to the accompanying figures in which:
The embodiments of the invention described herein are not intended to be exhaustive or to limit the invention to precise forms disclosed. Rather, the embodiments selected for description have been chosen to enable one skilled in the art to practice the invention.
As shown in
Equation 1 shows a calculation for the location of CG.
Equation 2 shows a normal force coefficient gradient summation.
Equation 3 shows a pitching moment coefficient gradient summation.
Equation 4 presents a calculation for the CoP.
Equation 5 expresses normal force coefficient gradient for small angles of attack.
In some embodiments, small angles of attack can be assumed, and a projectile'"'"'s cylindrical body 3 may not directly influence stability. The projectile'"'"'s boattail 5 CoP (e.g., as measured from the nose cone Xcp) can be minimized. An exemplary shorter cylindrical body 3 can move the boattail 5 closer to the nose cone 1, and can improve the CoP location. In some embodiments, CoP for the projectile'"'"'s boattail 5 normal force can be located at about 60% of the boattail 5 length downstream of a body-boattail juncture. The projectile'"'"'s boattail 5 normal force can also act in an opposite direction from the projectile'"'"'s nose cone'"'"'s 1 normal force. In this example, this means that the projectile'"'"'s boattail 5 can move a total CoP forward of a nose cone'"'"'s 1 CoP, which may be opposite from a desire effect (e.g., stability).
In some exemplary embodiments, a CG location in the subsonic projectile 11 can be brought closest to the projectile'"'"'s nose cone 1 tip as possible by varying materials in projectile'"'"'s 11 composition, such as, for example, aluminum, and tungsten, as shown in
In certain embodiments, a CG can also change when the projectile 11 has a long nose cone 1 in comparison to a short nose cone 1 of the same nose cone profile. Additionally, a CG can change when the projectile'"'"'s boattail 5 length is lengthened or shortened. In some embodiments, the longer the projectile'"'"'s nose cone 1, the more stable the projectile'"'"'s 11 flight can be. The projectile'"'"'s boattail 5 length can vary where an embodiment of a subsonic projectile has a long or short boattail 5 length that increases stability. In some exemplary embodiments, a short or long boattail 5 can be preferred, because a medium length boattail 5 can decrease stability.
In some embodiments, air around the projectile 11 can travel faster than the projectile 11, and can reach supersonic speeds before the projectile 11 does.
In some embodiments, a ballistic model can be created to show horizontal velocity decay as the projectile 11 travels down range.
An exemplary design can also include a focus on eliminating or reducing pressure drag (drag from airflow separating from the projectile) rather than reducing skin friction drag. To eliminate pressure drag in this embodiment, two elements of design were determined. First, an angle of the projectile'"'"'s tail (See
In other embodiments, given a streamlined body, most of a drag can be skin friction drag. If the projectile'"'"'s 11 velocity is below a critical Mach number and no flow separation occurs, then the projectile'"'"'s 11 pressure drag can be zero. Flow separation at subsonic speeds can cause significant pressure drag. Laminar and turbulent flow can impact flow separation. Laminar flow can provide for a lower skin friction drag; however, airflow can also separate from the body 3 causing a higher-pressure drag. Turbulent flow can have a higher skin friction drag; however, it does not separate as easily from the exemplary body 3 and therefore reduces the likelihood of pressure drag. Maintaining laminar flow can be difficult and can be impractical in some actual conditions. Designs or embodiments that prevent flow separation can create turbulent flow that can be worse than laminar flow that, in certain embodiments, can motivate to include design aspects that induce turbulent flow (e.g., by turbulence generators such as grooves 48).
Now referring to
An embodiment can also include a design to achieve consistent flight trajectory that can entail a design to maximize inflight stability. Several design elements and determinations were determined to maximize inflight stability in some exemplary embodiments. First, the boattail 5 length can be maximized based on the projectile 11 casing 20 used that can still fit into a chamber. A maximum boattail 5 length also can support a minimum tail angle θ and support a maximum initial velocity. Second, a length on the exemplary projectile'"'"'s body 3 can be minimized while keeping the projectile body'"'"'s 3 diameter constant and approximately equal to a caliber of a barrel sufficient to permit firing through the barrel without significant damage to the projectile 11. A short body 3 for stability conflicts with a long body 3 for maximum initial velocity. A trade-off can be accomplished whereas a minimum body 3 length can be selected for one embodiment. Third, the projectile'"'"'s 11 CG can be shifted as far forward as possible by means of, e.g., material selection or a composite of material. A trade-off in this exemplary embodiment can be that a longer boattail 5 pulls the CG to the rear that can impact stability. Different materials can be used to provide a long boattail 5 while pushing the CG as far forward as possible. Fourth, flat spots can be added to the boattail 5 to equalize pressure around the boattail 5 so the projectile 11 would be pushed straight from charge gas expansion and/or movement in the chamber and barrel (e.g. see rebated 45 and stepped 46 boattails in
In an exemplary embodiment, a critical Mach number can be used to determine a maximum subsonic velocity of the projectile 11. In some embodiments higher maximum projectile subsonic velocity creates improved ballistic properties that are balanced against other aspects of the invention. A Cp can be related to a freestream Mach number and a local velocity of the projectile 11. A projectile'"'"'s maximum critical Mach number and maximum Cp for the projectile 11 can be obtained by determining a freestream Mach number and relating it a minimum pressure coefficient.
Charge and temperature can impact subsonic external ballistics.
In certain embodiments, a stepped boattail 46 can be used, as shown in
A radius “r” of the projectile 11 at any given point x along the central axis 53, wherein the terminal tip 60 of the nose cone 1 is considered a value of 0 for x, can be calculated in the following manner. If x is greater than or equal to 0 but less than or equal to ln, the radius r is expressed by equation 6:
If x is greater than in but less than (ln+a·dmax) then the radius r is expressed by equation 7:
If x is greater than or equal to (ln+a·dmax) but less than or equal to it, then the radius r is expressed by equation 8:
Any number of grooves may be featured on the projectile 11. The grooves can have a plurality of possible profile shapes including a triangle-shaped cut and a square-shaped cut (as shown in
While various embodiments of an exemplary subsonic projectile could be extremely useful in military applications it can be beneficial in consumer markets. This can include use by varmint hunters wanting suppress sound created by their traditional supersonic firearm. This could also extend to larger game to allow for a potential follow up shot on a target.
Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the spirit and scope of the invention as described and defined in the following claims.