WO2024026425A1

WO2024026425A1 - Polymer coated lead-free projectile and method of making the same

Info

Publication number: WO2024026425A1
Application number: PCT/US2023/071149
Authority: WO
Inventors: Kevin GEIST; Mike SLOFF
Original assignee: Sinterfire
Priority date: 2022-07-27
Filing date: 2023-07-27
Publication date: 2024-02-01
Also published as: US20240035791A1

Abstract

A method of making a polymer-coated, lead-free projectile. In an embodiment, the method comprises compressing a lead-free metal powder to form a green core, heating the green core to bond the lead-free metal powder to form a metal compact of desired strength and placing the metal compact into fluidized bed of polymer to bond polymer to the metal compact to form a polymer coated compact. A polymer-coated, lead-free projectile made according to the described method, and a loaded round comprising the polymer-coated, lead-free projectile are also disclosed.

Description

DISCLOSURE

POLYMER COATED LEAD-FREE PROJECTILE AND METHOD OF MAKING THE SAME

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to Provisional Application 63/392,701, filed July 27, 2022. The entire contents of which is expressly incorporated herein by reference.

FIELD

[0002] The present disclosure generally relates polymer-coated, lead-free projectiles, such as polymer coated iron bullets. The present disclosure also relates to methods of making the polymer coated lead-free projectiles disclosed herein.

BACKGROUND

[0003] Compressed powder metal bullets are bullets comprised of powdered metal that are made using powdered metallurgy techniques. Such techniques include compressing powdered metal to form a green solid, then subsequently heat treating to obtain a desired metallurgical strength. Traditionally, these bullets were jacketed, plated or made to size in a centerfire or rimfire cartridge. Bullets made from compressed metal powder can be made “frangible” by altering the process to achieve a brittle microstructure. Such bullets are characterized by the use of metal powder consolidated into a bullet that has sufficient strength to maintain its integrity during firing while fragmenting on impact with a solid object.

[0004] The emission of airborne lead dust, and to the corresponding government regulations on the use and exposure to lead have led to nearly continuous search for a replacement of lead in bullets. Copper and copper alloys have become a popular substitute for lead bullets, especially in compressed powdered bullets. However, copper is a relatively expensive metal. [0005] Iron is typically not considered an ideal replacement for either lead or copper as it suffers from a number of problems. The primary issue with using iron as a bullet is that is it hard and light, both of which are bad properties for a bullet and lead to firing and accuracy issues. For example, an iron bullet will almost always have a higher hardness than barrel of the gun, which can result in eroding of the rifling in the barrel, and erosion of the barrel in general. In addition, iron oxidizes easily which could adversely affect the firing characteristics of the bullet.

[0006] To the extent the prior art teaches the use of polymers in powder metal bullets, it is usually as a binder for the metal particles, which can be applied by spraying the metal powder with resin or impregnating the metal compact with resin. Neither method solves the mentioned problems with iron containing bullets. As a result, the disclosed polymer-coated, lead-free projectile and method of making the same is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

[0007] To address the foregoing issues, there is disclosed a method of making a polymer-coated, lead-free projectile. In some embodiments, the method comprises compressing a lead-free metal powder to form a green core, heating the green core to bond the lead-free metal powder to form a metal compact of desired strength, and placing the metal compact that is at an elevated temperature into fluidized bed of polymer to bond polymer to the metal compact to form a polymer coated, lead-free projectile.

[0008] There is also disclosed a polymer-coated, lead-free projectile made according to the described method. In some embodiments, the polymer-coated, lead-free projectile is bullet made of iron and coated with a polymer coating made of Polyamide (PA), Polyetheretherketone (PEEK), or Polyetherketoneketone (PEKK), and having a thickness ranging from 0.005 to 0.010 inches.

[0009] A loaded round comprising the polymer-coated, lead-free projectile is also disclosed. In some embodiments, there is described a cartridge comprising: a metal cartridge case; a primer; a propellant within said cartridge case; and a polymer-coated, lead-free projectile as described herein.

[0010] Aside from the subject matter discussed above, the present disclosure includes a number of other features such as those explained hereinafter. Both the foregoing description and the following description are exemplary only.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1A is an illustration of various polymer-coated, lead-free projectiles consistent with the present disclosure. FIG. IB is a side representation of a bullet polymer- coated, lead-free projectiles consistent with the present disclosure.

[0012] FIG. 2 is the polymer-coated, lead-free projectile of FIG. 1A, shown as a loaded round consistent with the present disclosure.

[0013] FIG. 3 is a flowchart of an embodiment of the process used to make a polymer-coated, lead-free projectile described herein.

DETAILED DESCRIPTION

[0014] The present disclosure is related to a method of reducing the cost of lead- free projectiles by forming a projectile of mostly iron powder and coating the formed compact with a polymer. As described herein, a lead-free projectile is a type of ammunition that does not contain lead in its construction. Traditional bullets typically have a lead core surrounded by a copper or other metal jacket. However, lead has been a concern due to its potential environmental impact, especially when used in shooting ranges or hunting areas where lead can contaminate the soil and water.

[0015] Lead-free projectiles are designed as an alternative to mitigate these environmental concerns. There are several types of lead-free projectiles, each with its unique design and materials. Non-limiting examples of lead-free projectiles that can be made according to the present disclosure include iron-based bullets, copper-based bullets or frangible bullets. In some embodiments, iron-based bullets and copper-based bullets can also be frangible.

[0016] In some embodiments, copper-based bullets are projectiles made primarily and, in some embodiments, entirely of copper or a copper alloy. The absence of lead in the core eliminates the risk of lead contamination. Copper bullets can be solid copper, monolithic (one-piece), or have a polymer tip for improved ballistics.

[0017] In some embodiments, frangible bullets are made from a combination of metal powders and binding agents. These bullets are designed to disintegrate upon impact with a hard surface, such as steel targets or walls. The fragmentation reduces the risk of ricochets and minimizes damage to range targets.

Description of the Bullet

[0018] In accordance with the present disclosure, a metal projectile, such as a polymer-coated, lead-free bullet, is provided as described and claimed herein. In some embodiments, there is disclosed a polymer-coated bullet or projectile in which at least a portion of the bullet's exterior surface, and in some embodiments, the entirety of the surface, is coated with a thin layer of polymer material. This coating may provide an alternative to traditional lubricants or copper jackets commonly found on bullets. Polymer-coated bullets have additional benefits, including less barrel wear, and potentially enhanced accuracy.

[0019] In some embodiments, the polymer coating acts as a dry lubricant, reducing the need for traditional wax or oil-based lubricants that are commonly used to prevent lead fouling and barrel buildup. The polymer coating provides a low-friction surface, allowing the bullet to move smoothly through the barrel.

[0020] In some embodiments, the polymer coating can help protect the firearm's barrel from the abrasive effects of traditional copper-jacketed bullets. It can also reduce copper fouling, which occurs when small amounts of copper from the bullet's jacket are deposited in the barrel during shooting.

[0021] In some embodiments, the polymer coating is relatively thin and does not significantly alter the bullet's weight or shape. Additionally, the polymer coating does not affect the ballistics or terminal performance of the bullet, meaning it will still perform as intended for a particular application. Polymer coatings used to coat bullets are typically specially formulated for this specific application. They are designed to provide the desired lubrication, protection, and environmental benefits while adhering to the surface of the bullet effectively.

[0022] The bonding between polymers and metal materials to form a polymer- coated metal can occur through various mechanisms. In some embodiments, bonding between polymers and metals occurs through adhesion, which is the physical interaction between the polymer and metal at their interface. For example, bonding occurs due to attractive forces between the polymer molecules and the metal surface. Adhesion promotes strong and durable bonding in polymer-coated metals.

[0023] In some cases, chemical bonding can occur at the interface between the polymer and metal. This involves the formation of covalent bonds or other chemical interactions between the polymer molecules and metal atoms or functional groups on the metal surface. Chemical bonding can also provide a very strong and permanent bond between the polymer and metal, enhancing the coating's durability.

[0024] In one embodiment, there is disclosed a lead-free bullet comprising a compacted mixture of iron powder, wherein the iron powder comprises particles that are physically bonded to each other to form a cohesive and microstructure. A cohesive microstructure allows for crimping and rifling. While the iron powder particles can be sintered, alternative or additional embodiments include iron powder particles that are bonded by pre-sintering or partial sintering. This ability to vary the bond strength between particles from sintered to pre-sintered states allows for flexibility in the frangibility properties of the resulting bullet. As used herein, “partial sintering” or “pre-sintering” is intended to mean that some neck growth has developed between particles; however, porosity remains between adjacent particles.

[0025] In an embodiment the metal powder comprises iron, which can be mixed with at least one additional metal powder, a mixture of powders or alloys thereof. Examples of such additional metal powders include (in addition to iron) copper, zinc, chromium, tungsten, bismuth, nickel, tin, boron, tungsten and/or alloys thereof, and/or oxides thereof. In one embodiment the metal powder includes a sintering aid. In another embodiment the sintering aid is phosphorous or boron.

[0026] In an embodiment the bullet may comprise an admixed lubricant that aids in processing, primarily in the pressing steps that allows in ease of pressing and release from the mold. Non-limiting examples of the lubricant that can be used include molybdenum disulfide, zinc stearate, lithium stearate, carbon, synthetic wax, such as N,N’ Ethylene Bis- Stearamide or N,N’ Distearoylethylenediamine (sold as Acrawax® by Lonza), polytetrafluoroethylene (sold as Teflon® by DuPont Co.), polyethylene, polyamide, and polyvinyl alcohol, and combinations of any of the foregoing.

[0027] In one embodiment, the bullet described herein is not loaded. To exemplify this product, reference is made to FIG. 1A, which illustrates an unjacketed bullet 100 with a polymer coating 103 on only part of the bullet, and an exposed area having no coating 104. The uncoated area is illustrative only. In practice, the entirety of the bullet 100 would be coated with polymer coating 103. In one embodiment, the bullet described herein is used in a pistol product. To exemplify this product, reference is made to FIG. IB (101). There is shown pistol product (101) that is completely covered with a polymer coating, including the heel or base (105), a driving band (110), and a nose portion (112), which comprises a meplat (115), which is the tip portion of the nose, and an ogive (120), which is the radius portion that connects the body to the bullet nose.

[0028] A loaded round according to some embodiments 200 is shown in FIG. 2. This figure illustrates the polymer coated bullet (210) in a metal jacket (220). Similar to FIG. 1A, FIG. 2 illustrates the bullet 210 with a polymer coating 203 on only part of the bullet, and an exposed area having no coating 204. Again, the uncoated area is illustrative only. In practice, the entirety of the bullet 210 would typically be coated with polymer coating 203.

Description of Method of Making the Bullet

[0029] In accordance with the present disclosure, there is disclosed a method of making a polymer-coated, lead-free projectile that does not use the polymer as a binder for the metallic particles. In some embodiments, the process of making a bullet using powder metallurgy involves several steps to form the bullet shape from metal powders. In some embodiments, the first step is to prepare the metal powders that will be used to make the bullet. The metal powders are typically produced by processes such as atomization, mechanical milling, or chemical reduction. The metal powders, which may primarily include iron, can then be mixed to ensure a homogeneous composition. The blended metal powders can then be loaded into a die and pressed under high pressure using a mechanical or hydraulic press. The pressure compacts the powders, forming a green compact, which is a loosely bonded preform in the shape of the bullet. Next, the green compact may be subjected to a heating step to form a rigid structure. When frangibility is required, heat treatment occurs at conditions below sintering conditions. These conditions may include lower temperatures and shorter times or both in order to form a “pre-sintered” product. The goal of a pre-sintered product is to form a compact that causes the metal particles to begin to fuse together but not result in a fully dense and solid bullet shape. Alternatively, it is possible to heat treat to a higher temperature and at conditions to fully sinter the metal particles into a fully (or nearly fully) dense, solid bullet shape.

[0030] After heat treating, the bullet is cooled, but not to room temperature. While still in an elevated temperature, such as at or above 200 degrees Fahrenheit, the heat treated bullets undergo a polymer coating processes described herein.

[0031] In some embodiments, the method comprises compressing a lead-free, iron containing metal powder to form a green core. As used herein a green body refers to a pressed bullet or projectile formed from the raw materials, including the metallic particles, that has not yet undergone the final heat treatment processing step, such as sintering. In some embodiments, the process of creating a green body involves shaping or forming the raw material into a desired shape, typically through pressing. Once the green body is formed, it is not yet fully dense or consolidated, and additional processing is required to achieve the final properties and desired characteristics.

[0032] In some embodiments, the method further comprises heating the green core to bond the lead-free metal powder to form a metal compact of desired strength, and placing the metal compact that is at an elevated temperature into fluidized bed of polymer to bond polymer to the metal compact to form a polymer coated, lead-free projectile.

[0033] In some embodiments, a fluidized bed reactor for applying a polymer coating applies a thin and uniform layer of polymer material onto the metal compact. This process is known as fluidized bed coating generally works in the following way:

[0034] Coating Material Preparation: The polymer coating material is prepared in the form of fine powder or granules. The polymer can be a thermoplastic material, such as nylon, polyethylene or polypropylene, or a thermosetting material that will cure upon heating.

[0035] Bed Preparation: The reactor contains a bed of lead-free metal compacts that require coating.

[0036] Fluidization: A gas, typically air, is introduced into the bottom of the reactor, passing through a distributor plate. The flow rate of the gas is controlled to achieve a fluidization velocity that is just enough to lift and suspend the lead-free metal compacts within the reactor.

[0037] Coating Application: The polymer coating material is introduced into the fluidized bed. The upward flow of gas lifts and suspends the lead-free metal compacts, causing them to behave like a fluid. As the lead-free metal compacts move through the fluidized bed, they come into contact with the polymer coating material, which adheres to their surfaces, forming a thin, even layer.

[0038] In some embodiments, a heat treatment step may be included to cure or solidify the polymer coating. This is often necessary for thermosetting materials that require a specific curing temperature and time to achieve the desired properties.

[0039] In some embodiments, once the coating process is complete, the coated lead- free metal compacts are separated from the fluidized bed. This can be done using a discharge port at the bottom of the reactor, where the coated pieces are collected. [0040] Fluidized bed coating offers several advantages for applying polymer coatings. Non-limiting examples of such advantages include a uniform coating: The fluidization of particles ensures that the coating material evenly covers the entire surface of lead-free metal compact, resulting in a uniform coating thickness.

[0041] In addition, fluidized bed coating is a continuous process, allowing for high production rates and efficient use of coating materials. Also, the fluidization velocity can be adjusted to control the coating thickness, making it suitable for various coating applications.

[0042] In some embodiments, the method of heating the green core to bond the lead-free metal powder to form a metal compact is dependent upon the metal particles used to make the compact, as well as the desired density and strength of the resulting compact. In one embodiment in which the metal compact comprises is made primarily of iron heating is performed at a temperature ranging from 1000 to 2000 degrees Fahrenheit.

[0043] While still hot, such as above 200 degrees Fahrenheit, such as within the range of 200 to 1000 degrees Fahrenheit, or even in the range from 400-800 degrees Fahrenheit for nylon, the heated metal compact is placed into a desired polymer. As indicated, one non-limiting example of the polymer is Nylon, with a particular mention of Nylon 11. Nylon 11, also known as Polyamide 11 (PA 11), is a high-performance thermoplastic material that exhibits excellent mechanical properties, including high tensile and flexural strength. Nylon 11 has a relatively low density compared to many other engineering thermoplastics, which contributes to its lightweight nature and its suitability in the present application. In addition, Nylon 11 offers exceptional wear resistance and low coefficient of friction, which also renders it suitable for the present application. Other beneficial properties that make Nylon 11 suitable for the present application are its chemical resistant properties, low water absorption compared to many other nylons, which helps maintain its mechanical properties and dimensional stability even in humid environments. [0044] More broadly, other thermoplastic polymers that can withstand temperatures of 250 degrees Fahrenheit (121 degrees Celsius) can be used if it exhibits other properties necessary to withstand the firing conditions. Such properties include: mechanical strength that retains its strength and stiffness even at high temperatures, allowing it to withstand mechanical loads and stresses at elevated operating conditions; chemical resistance to a wide range of chemicals, including many solvents and aggressive substances; low flammability that is inherently flame-resistant and has low smoke emission; and excellent dimensional stability, even at high temperatures, which could be critical in the disclosed application where tight tolerances are required.

[0045] In addition to Nylon 11, other non-limiting examples of polymers that exhibit one or more of the foregoing properties include, Polyetheretherketone, commonly known as PEEK. PEEK is a high-performance engineering thermoplastic known for its exceptional thermal and mechanical properties, making it suitable for the disclosed application. Non-limiting examples of other thermoplastic materials that have a glass transition temperature (Tg) above 250 degrees Fahrenheit (121 degrees Celsius), and offer excellent mechanical, thermal, and chemical properties, making them suitable as a coating include: Polyimide (PI), Polyphenylene Sulfide (PPS), Polyetherimide (PEI), Polyetherketone (PEK), Polyetherketoneketone (PEKK), Polysulfone (PSU), and Polyetheretherketoneketone (PEEKK).

[0046] In one embodiment, the metal compact is coated with polymer to form a polymer coating having a thickness ranging from 0.001 to 0.030 inches, such as from 0.005 to 0.010 inches.

[0047] The disclosed process can be used with any thermoplastic. In one embodiment, a fluid bed process is used. For example, a MaxiCoat® process (Collt Mfg. Fluidized Bed coating process) that uses powder fluidized through vibration may be used. The parts could also be coated with a spray on system as well to have a similar outcome. The bullet is placed into the desired polymer at an elevated temperature to ensure that no moisture is present immediately before it is coated, thereby eliminating the risk.

[0048] However, other metals in addition to or instead of iron, may be used in the compact, including copper, zinc, tungsten, bismuth, nickel, tin, boron, tungsten and/or alloys thereof, and/or oxides thereof.

[0049] In an embodiment the projectile may comprise an admixed lubricant that aids in processing, primarily in the pressing steps that allows in ease of pressing and release from the mold. Non-limiting examples of the lubricant that can be used include molybdenum disulfide, zinc stearate, lithium stearate, carbon, synthetic wax, such as N,N’ Ethylene Bis- Stearamide or N,N’ Distearoylethylenediamine (sold as Acrawax® by Lonza), polytetrafluoroethylene (sold as Teflon® by DuPont Co.), polyethylene, polyamide, and polyvinyl alcohol, and combinations of any of the foregoing.

[0050] In one embodiment, there is disclosed a method of making a coated, lead free bullet. With specific reference to FIG. 3, the particular steps of an embodiment of a method 300 for preparing a bullet as disclosed are shown. The bullet is produced from a lead-free metal containing powder following principles of the present disclosure. For example, the required lead-free metal containing powder, may primarily (or solely) comprise iron is provided, and optionally mixed with a lubricant, examples of which were previously described (step 310).

[0051] The powder is then pressed which is compacted, under pressure using known compacting techniques, such as die compaction, rotary screw compaction, isostatic pressing, to form a shaped green core of uniform density (step 320). In an embodiment, the compacting step is performed at room temperature, which may be referred to as “cold compaction.” In another embodiment, the compacting step is performed under heating conditions. In this embodiment, the powder is heated before pressure is applied to the material. It is understood that this heating step is done at a temperature that does not adversely affect other components present in the powder, such as the previously described lubricants. Alternatively, the heating step is performed at a high enough temperature that allows for sufficient compaction with a reduced amount of lubricant.

[0052] The green core is then heat treated at a temperature below the melting point of lead-free metal containing powder, and in some embodiments, below the sintering point of such metals (step 330). Heating the green core is performed at a temperature that will bond the lead-free metal powder to form a metal compact of desired strength for subsequent processing conditions, including but not limited to those described below.

[0053] While still at an elevated temperature, such as above 400 degrees Fahrenheit, the placing the metal compact that is at an elevated temperature into fluidized bed of polymer to bond polymer to the metal compact to form a polymer coated, lead-free projectile (step 340).

[0054] Other optional processing steps that can be performed on the bullet described herein (350). For example, in various embodiments, the bullet can be processed to include one or more cannelure grooves, a tipped point, a hollow point, boat-tailed, a ring (multiple groves), and combinations thereof, OD size qualification, nose markers, customer specific requirements, etc. The optional processing steps may include one or more tumbling steps to affect the surface (step 340). In addition, the bullet can be loaded into a casing, such as a brass casing, to make ammunition of various calibers (step 350). A more detailed discussion of the cartridge is provided below.

[0055] In some embodiments, the disclosed polymer-coated, lead-free projectile, and method of making it are applicable to the making both bullets and loaded ammunition, such as a rifle cartridge. Non-limiting embodiments of rifle cartridges that can be made according to the present disclosure include the following calibers: .22, including a .22 long rifle, .223, .308, .338, or any pistol/rifle cartridge. In addition, 5.56 caliber, 7.62 caliber rifle cartridges can be produced according to the present disclosure.

Description of the Cartridge

[0056] As indicated, in one embodiment, the disclosed polymer-coated, lead-free projectile is a bullet that can be loaded in a cartridge. An ammunition cartridge, often simply referred to as a "cartridge," is a self-contained unit that contains all the components necessary to fire a single shot from a firearm. Cartridges come in various sizes and configurations, tailored to the specific requirements of different firearms and shooting applications. A typical ammunition cartridge consists of the following components:

[0057] Cartridge Case: The cartridge case is the outer container that holds all the other components together. In some embodiments, it is made of metal, such as brass, steel, or aluminum, and has a cylindrical shape. The case acts as a container for the propellant (gunpowder) and the bullet, and it provides the means of extracting and ejecting the fired cartridge from the firearm's chamber.

[0058] Primer: The primer is a small, sensitive, and impact-sensitive explosive compound located in the base of the cartridge case. It serves as the ignition source for the ammunition. When struck by the firing pin or hammer of the firearm, the primer ignites, producing a flame that travels through a small flash hole into the cartridge case. This ignition ignites the gunpowder, initiating the firing process.

[0059] Propellant: In some embodiments, the propellant, is a chemical mixture inside the cartridge case. When ignited by the primer's flame, it rapidly bums and creates a large volume of hot gas. The expanding gas creates pressure within the cartridge case, which propels the bullet out of the case and down the barrel of the firearm. [0060] The process of using an ammunition cartridge involves loading it into the firearm's chamber. When the trigger is pulled, the firearm's firing pin strikes the primer at the cartridge's base. The primer ignites, creating a flame that travels through the flash hole and ignites the gunpowder. The burning gunpowder produces high-pressure gas that propels the bullet out of the cartridge case and down the barrel, ultimately being directed towards the target.

[0061] Cartridges are manufactured in various calibers to suit different firearm types and purposes, ranging from small handgun calibers to large rifle calibers. They are an essential component of modern firearms and have significantly contributed to the convenience, safety, and effectiveness of shooting activities.

[0062] A centerfire cartridge is a type of ammunition used in firearms. It is one of the most common types of cartridges and is widely used in rifles, handguns, and some types of shotguns. The term "centerfire" refers to the location of the primer, which is located at the center of the cartridge case base. In some embodiments, centerfire cartridges are used for higher-powered firearms and more significant calibers due to their greater reliability and ability to withstand higher pressures. They offer a wide range of applications and have been widely adopted for various shooting purposes due to their efficiency and versatility.

[0063] A rimfire cartridge is a type of ammunition used in firearms, particularly in smaller calibers and low-powered handguns and rifles. Unlike centerfire cartridges, which have the primer located at the center of the cartridge case base, rimfire cartridges have the primer distributed around the inside rim of the cartridge base.

[0064] In some embodiments, a conventional centerfire cartridge can be used with the disclosed bullet, however, a rimfire cartridge can also be used for pistol and rifle rounds. For example, the disclosed bullet can be inserted in the case mouth, which can then be crimped to assist in retaining the bullet at the desired depth of insertion. The bullet described herein has sufficient strength and ductility to withstand the crimping operation without fracturing during crimping.

[0065] In an embodiment, the case further includes a primer pocket into which a separate primer can be inserted. As mentioned, the case can be a straight walled case typical of pistol ammunition. Alternatively, bullets described herein are also useful as rifle ammunition and for such ammunition the case may be a “bottle necked” cartridge, with the case mouth having a diameter less than the body of the cartridge case.

[0066] In an embodiment, the propellant (gun powder) can be placed in the body of the cartridge case. In an embodiment, the primer, like the bullet, is lead-free. However, it is understood that any conventional primer may be used. The described cartridge may comprise a metal cartridge case, a primer, a propellant within said cartridge case, a bullet comprising a polymer-coated, lead-free projectile.

[0067] The bullet disclosed herein exhibits characteristics sufficient to withstand circumferential crimping. For example, the disclosed bullet exhibits density and malleability properties that allow it to be loaded into a cartridge and crimped. Such properties include a density ranging from 6.0 to 7.6 g/cc, such as 6.5 to 7.0 g/cc, or even 6.6 to 6.8 g/cc and metallic bonds between a majority of the iron powder particles in the bullet.

[0068] In one embodiment, the resulting loaded bullet has a pull-out force ranging from 25 to 50 lbs, such as from 30 to 50 lbs, 35 to 50 or even 40 to 50 lbs. of pull-out force for a pistol bullet. The pull-out force for a rifle cartridge is typically twice that of a pistol bullet, often being over 100 lbs.

Mechanical and Ballistic Testing

[0069] Loaded rounds were tested for ensure that they achieved a maximum average pressure within SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) specifications. As shown below in Table 1, the test revealed that ammunition made according to the present disclosure met the maximum average pressure limits set by SAAMI for each standardized cartridge.

Table 1. Results of SAAMI Testing

* The "average pressure" refers to the average of several pressure readings taken during the test. It is noted that the ammunition tested did not exceed this pressure limit, and thus is within SAAMI specifications.

[0070] Velocity testing of the ammunition described herein was used to measure both the velocity of the bullet, and how it affects its trajectory, accuracy, and terminal performance. Results of that testing are provided in Table 2.

Table 2. Results of Ballistic Testing

[0071] The combination of the S AAMI test and velocity test showed that in some embodiments, the disclosed methods reproducibly produce a bullet having accurate ballistic properties, including trajectory and bullet drop. In addition, the disclosed tests evidence that the ammunition meets consistent performance standards, which is crucial for accuracy and safety.

[0072] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed alloy and method of forming the alloy into a finished part without departing from the scope of the disclosure. Alternative implementations will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

[0073] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being indicated by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of making a polymer-coated, lead-free projectile, said method comprising: compressing a lead-free metal powder to form a green core having a density ranging from 6.0-7.6 g/cc; heating the green core to bond the lead-free metal powder to form a metal compact of desired strength; and placing the metal compact that is at an elevated temperature into fluidized bed of polymer to bond said polymer to the metal compact to form a polymer coated, lead-free projectile, wherein the polymer has a glass transition temperature of at least 250 degrees Fahrenheit.

2. The method of claim 1, wherein heating is performed at a temperature ranging from 1000-2000 degrees Fahrenheit.

3. The method of claim 1, wherein the lead-free metal powder comprises iron, copper, zinc, tungsten, bismuth, nickel, tin, boron, tungsten and/or alloys thereof, and/or oxides thereof.

4. The method of claim 3, wherein the lead-free metal powder comprises iron.

5. The method of claim 1, wherein the polymer comprises Polyamide (PA), Polyimide (PI), Polyphenylene Sulfide (PPS), Polyetherimide (PEI), Polyetherketone (PEK), Polyetheretherketone (PEEK), Polyetherketoneketone (PEKK), Polysulfone (PSU),

Poly etheretherketoneketone (PEEKK) .

6. The method of claim 5, wherein the polymer comprises Polyamide (PA), Poly etheretherketone (PEEK), or Poly etherketoneketone (PEKK).

7. The method of claim 6, wherein the Polyamide (PA) is nylon- 11.

8. The method of claim 1, wherein the lead-free metal powder comprises iron and the compact exhibits a density ranging from 6.5 to 7.0 g/cc.

9. The method of claim 1, wherein said elevated temperature is above 200 degrees Fahrenheit.

10. The method of claim 1, further comprising at least one step to introduce into the polymer-coated, lead -free projectile at least one design chosen from a cannelure groove, a tipped point, a hollow point, boat-tail, ring, a grove, and combinations thereof.

11. The method of claim 1, further comprising at least one post processing step to size the polymer-coated, lead-free projectile to achieve a desired diameter.

12. The method of claim 1, wherein the projectile comprises a frangible metal bullet.

13. The method of claim 1, further comprising loading the polymer-coated, lead- free projectile into a cartridge.

14. The method of claim 1, wherein the metal compact is placed in the fluidized bed of polymer to form a polymer coating having a thickness ranging from 0.001 to 0.030 inches.

15. The method of claim 14, wherein the polymer coating has a thickness ranging from 0.005 to 0.010 inches.

16. A polymer-coated, lead-free projectile made according to the method according to claim 1.

17. The polymer coated, lead free projectile of claim 16, wherein the projectile is bullet made of a iron and coated with a polymer coating made of Polyamide (PA), Polyetheretherketone (PEEK), or Polyetherketoneketone (PEKK), and having a thickness ranging from 0.005 to 0.010 inches.

18. A cartridge comprising: a metal cartridge case; a primer; a propellant within said cartridge case; a polymer-coated, lead-free projectile according to claim 16.

19. The cartridge of claim 18, wherein said cartridge is a rimfire cartridge or a centerfire cartridge.

20. The cartridge of claim 18, wherein cartridge is a rifle cartridge, or a pistol bullet/cartridge.