LEAD-FREE TIN PROJECTILE

Abstract: There is provided a lead-free projectile (10, 30, 40, 42, 44) suitable for use as a bullet to be fired from a pistol or rifle. The projectile has a metallic jacket (12, 46) enveloping a metallic core (16). The core is formed from a high purity tin and has deformation properties similar to that of lead based projectiles without the environmental hazards associated with lead.

Description: LEAD-FREE TIN PROJECTILE This invention relates to a lead-free projectiles fired from rifle and pistols. More particularly, a copper jacketed bullet having an essentially pure tin core exhibits performance characteristics similar to lead without presenting the environmental hazards of lead. Most bullets fired from pistols and rifles have a lead base core alloy core, meaning the core is either entirely or more than 50%, by weight, lead. The environmental hazards of lead are well known. Lead containing bullets fired into the ground are suspected to cause ground water pollution through leaching. Another problem facing shooters is that when a bullet having exposed lead is fired, a lead-containing dust from the projectile is emitted. These lead fumes are toxic and, if inhaled, present a hazard to the shooter. An additional hazard, lead is leached into ground water from unrecovered bullets. Many alternatives to a lead core bullet have been disclosed. United States Patent No. 5,399,187 to Mravic et al. discloses a sintered bullet core formed from a combination of a material having a density less than lead and a second material having a density greater than lead. One disclosed combination is a mixture of tin and tungsten. United States Patent No. 5,500,183 to Noordegraaf et al. discloses a non-jacketed bullet formed from a tin base alloy that contains as an alloy addition one or more of copper, antimony, bismuth and zinc. United States Patent No. 5,679,920 to Hallis et al. discloses jacketed bullets having a core formed from twisted and swaged strands of zinc wire. While the bullets disclosed in the above United States patents are lead- free, the cores of these bullets are harder than lead causing the bullets to have an unacceptable degree of ricochet. In addition, zinc containing cores may also pose an environmental hazard. Zinc fumes are noted in the ASM Handbook. Volume 2 as suspected to have a detrimental effect on health. There remains, therefore, a need for a projectile that is both lead- free and zinc- free and has performance characteristics similar to that of a bullet with a lead base core. Among the performance characteristics of lead that enhance bullet performance are malleability, density and low cost. Accordingly, it is an object of the invention to provide a lead-free projectile with upset characteristics similar to that of lead without the environmental hazards of lead. It is a feature of the invention that the projectile has an essentially pure tin core surrounded by a copper alloy jacket. Among the advantages of the invention are that the projectile has upset characteristics similar to that of lead and, by being lead-free, has a reduced impact on the environment. The projectiles are suitable for all types of jacketed bullets, including pistol and rifle. The projectiles of the invention are useful for soft point, partition, and hollow point bullets, as well as other bullet configurations. In accordance with the invention, there is provided a lead- free projectile. The lead- free projectile has a metallic jacket with an outer surface defining an aerodynamic projectile and an inner surface defining at least one cavity. The at least one cavity is filled with essentially pure tin that has a yield strength of less than 20 MPa. The above stated objects, features and advantages will become more apparent from the specification and drawings that follow. Figures 1 and 2 illustrate in cross-sectional representation rifle bullets in accordance with the invention. Figures 3-5 illustrate in cross-sectional representation pistol bullets in accordance with the invention. With reference to Figure 1, a projectile 10 in accordance with the invention has a metallic jacket 12. The metallic jacket 12 has an inner surface 14 defining at least one cavity that is filled with a core material 16 that is lead-free. Lead-free, is intended to mean that lead is intentionally added as an alloying addition. While, from an environmental stand-point, zero lead is desired, incidental lead impurities, in an amount of up to 0.05%, by weight, is within the scope of the invention. A preferred core material 16 is essentially pure tin. An outer surface 18 of the metallic jacket 12 has an aerodynamic profile. Typically, the outer surface is generally cylindrical in shape with an inwardly tapered frontal portion 20, a central portion 22 of substantially constant diameter and a heel portion 24 is generally perpendicular to the body portion 22. A transition portion 26 between the body portion 22 and heel portion 24 may be a relatively tight radius, or, as illustrated in Figure 1 , a tapered portion, referred to as a boat tail. The metallic jacket 12 is formed from any suitable material such as copper, aluminum, copper alloys, aluminum alloys or steel. Copper base alloys containing zinc are preferred with a copper gilding alloy (nominal composition by weight of 95% copper and 5% zinc) being most preferred. The core material 16 is formed from a metal having deformability characteristics similar to that of lead. Lead alloy L50042 (nominal composition by weight, 99.94% lead minimum) has a yield strength of between 12 and 14 MPa. Grade A pure tin (nominal composition by weight of 99.85% tin minimum) has a yield strength of 11.0 MPa. Preferably, the metallic cores of the invention have a yield strength that is less than 20 MPa and, preferably, the yield strength is from about 8 MPa to about 15 MPa. The hardness is less than 20 HB, and preferably, from about 3 to about 5 HB. Both yield strength and hardness values are at room temperature, between about 20°C and 23°C. As illustrated in Table 1, small additions of most alloying elements increases the yield strength and hardness of a tin base core. The less deformable the core, the greater the risk of ricochet. Table 1 A preferred metallic core 16 is essentially pure tin. The tin base core has a maximum, by weight, of 0.5% in total of alloying additions and no more than 0.25%, by weight, of any one alloying addition. More preferably, the total amount of all alloying additions is less than 0.2%), by weight, with no more than 0.1 %, by weight, of any one alloying addition. Certain elements suspected to generate toxic fumes or to cause environmental hazards should be present in lesser amounts. As delineated in the ASM Handbook, at Volume 2, these detrimental additions include arsenic, lead, cadmium and zinc. Each detrimental addition is preferably present in an amount, by weight, of less than 0.005% and, more preferably, in an amount of less than 0.002%. A preferred material for the metallic core is specified by ASTM (American Society for Testing and Materials) as Grade A tin. This metal has a minimum tin purity, by weight, of 99.85% tin and maximum residual impurities of 0.04% antimony, 0.05% arsenic, 0.030% bismuth, 0.001% cadmium, 0.04% copper, 0.015% iron, 0.05% lead, 0.01% sulfur, 0.005% zinc and 0.01% (nickel + cobalt). Alloying additions that do not significantly change the yield strength or hardness of the tin base alloy may be present in larger amounts. For example, it is believed that magnesium additions of, by weight, up to 5% and, preferably, from about 1.5% to about 2.5% are suitable. The essentially pure tin is heated to above its melting temperature and molten metal poured into a cup-shaped jacket precursor. The jacket precursor is then mechanically swaged to a desired jacket shape. Figure 1 illustrates a projectile 10 suitable as a jacketed soft point rifle bullet. The density of tin, 7.17 grams per centimeter 3 , is about 63% that of lead, 11.35 g/cm 3 . Therefore, the projectiles of the invention have a weight that is lower than the weight of a lead cored projectile of equivalent dimensions. The reduced weight does not significantly degrade the performance of pistol bullets intended for short range use. For rifle bullets, a minor increase in bullet length, will achieve a bullet weight similar to a lead core projectile. For example, a 5.56 millimeter copper jacketed soft point projectile, of the type illustrated in Figure 1, has a nominal length of 0.675 inch (1.7 cm) and full weight of 55 grain (3.56 g) when formed from lead. By increasing the length to 0.825 inch (2.10 cm), a projectile with an essentially pure tin core achieves the same weight. Figure 2 illustrates a second projectile 30 useful as a rifle bullet. The projectile 30 has a partition design with a hollow point nose 32 formed from a metallic jacket 12. The metallic jacket 12 defines a rearward cavity filled with essentially pure tin 16. A closure disk 34, typically formed from brass, is press-fit into the heel portion 24 of the projectile 30 to prevent the extrusion of tin when the projectile is rapidly accelerated during firing. Optionally, one or more cup-shaped inserts 36 are disposed between the essentially pure tin 16 and the hollow point nose 32. As disclosed in United States Patent No. 5,385,101 to Corzine et al., the cup-shaped insert 36, or multiple inserts, minimize the extrusion of metallic material from the cavity into a game animal struck by the projectile 30. The integrity of the metallic jacket 12 may be breached by impact with bone, or other hard structure, or pierced by petalled tips of the hollow point nose. The cup-shaped inserts 36 provide extra strength to prevent the loss of the core material. Figures 3-5 illustrate projectiles of the invention suitable for firing from a pistol. Figure 3 illustrates a projectile 40 referred to as a jacketed soft point pistol bullet. The nose portion 41 is formed from essentially pure tin. Exemplary calibers for the projectile 40 are a 9 millimeter Luger jacketed soft point projectile, .38 Special jacketed soft point projectile, .40 S&W jacketed soft point projectile, .45 Auto copper jacketed soft point projectile, 5.56 mm jacketed soft point projectile and 10 mm Auto jackets soft point projectile. Structures illustrated in Figures 3-5 that are similar to those illustrated and described in Figures 1 and 2 are identified by like reference numerals. The projectile 42 illustrated in Figure 4 is a jacketed hollow point projectile. The nose portion 41 includes a rearwardly extending, forwardly open annular cavity 43. Optionally, the nose portion 32 of metallic jacket 12 extends into the open annular cavity 43. One exemplary caliber for this projectile is a 9 millimeter Luger copper jacketed hollow point bullet. Figure 5 illustrates a partition hand gun projectile 44. A generally H-shaped, partition, metallic jacket 46 has a centrally disposed partition portion 47 separating a rear cavity 48 and a forward cavity 50. Both the rear cavity 48 and the forward cavity 50 are filled with the metallic core material 16. A closure disk 34 may be press-fit to the heel portion 24 of the metallic jacket 46 to retain the metallic core material 16 in the rearward cavity 48. The projectiles of the invention are suitable for use with any conventional cartridge, including without limitation, center-fire pistol, center- fire rifle, center-fire revolver and rim- fire. The projectiles are not limited to specific calibers and the essentially pure tin cores of the invention are suitable for any jacketed projectile presently having a metallic lead core. Projectiles of a size effective to be fired from a pistol utilizing a center-fire cartridge range in size from .25 caliber to about .458 caliber and projectiles of a size effective to be fired from a rifle utilizing a center- fire cartridge range in size from .22 caliber to about .50 caliber. Projectiles for rim-fire cartridges are typically .22 caliber for both pistol and rifle. While the projectiles of the invention are particularly designed to be at least partially encased within a metal jacket, it is within the scope of the invention to form unjacketed projectiles from the essentially pure tin material disclosed hereinabove, particularly for firing from a pistol. The advantages of the invention will become more apparent from the examples that follow. EXAMPLES Example 1 9 millimeter Luger copper jacketed soft point projectiles, of the type illustrated in Figure 3, were manufactured with an essentially pure tin core and firing tests were performed using a 9 millimeter Luger SAAMI (Sporting Arms and Ammunition Manufacturers Institute) standard test barrel. All tested bullets were found to possess optimum interior and exterior ballistic properties in addition to a predictable bullet flight, accuracy and low ricochet potential. Due to the density of tin being lower than that of lead, the 9 millimeter Luger projectiles of the invention weighed an average of 105 grains (6.80 g), compared to a conventional lead core 9 millimeter Luger bullet of similar design that weighed an average of 147 grains (9.53 g). Example 2 .40 Smith & Wesson (S&W) copper jacketed soft point projectiles were manufactured with an essentially pure tin core. Firing tests were performed with these bullets using a .40 S&W SAAMI standard test barrel. All bullets were found to possess optimum interior and exterior ballistic properties in addition to a predictable bullet flight, accuracy and low ricochet potential. Due to the density of tin being lower than that of lead, the .40 S&W projectiles of the invention had an average bullet weight of 140 grains (9.07 g) as compared to a conventional .40 S&W designed with the same dimensions having an average bullet weight of 180 grains (11.66 g). Example 3 9 millimeter Luger copper j acketed hollow point proj ectiles, of the type illustrated in Figure 4, were manufactured with an essentially pure tin core. Firing the projectiles from a 9 millimeter Luger standard test barrel demonstrated that all bullets had optimum interior and exterior ballistic properties in addition to a predictable bullet flight, accuracy and low ricochet projectile. The 9 millimeter jacketed hollow point projectiles of the invention had an average weight of 104 grains (6.74 g) compared to 147 grains (9.53 g) for comparable standard production material 9 millimeter Luger jacketed hollow point bullets. Ten of the bullets of the invention were loaded in a standard 9 millimeter Luger shell case with Ball Powder® propellant ("BALL POWDER" is a trademark of Primex Technologies, Inc., St. Petersburg, Florida. The propellant is available from Olin Corporation, East Alton, Illinois) to a loaded round length of 1.115 inches (2.832 cm) ± 0.010 inch (0.025 cm). The projectile velocity on firing was 1,100 feet per second (335 m/s) ± 20 feet per second (6 m/s). In accordance with Federal Bureau of Investigation ammunition test protocol, five of the bullets of the invention were fired into a block of gelatin from a distance of 10 feet (3.05 m). The bullets had an average velocity of 1,144 feet per second (348.7 m/s) and penetrated the gelatin to an average depth of 11.15 inches (28.3 cm). Another five shots were fired at a gelatin block covered with a layer of denim covered by a layer of down. The bullets were fired from a distance of 10 feet (3.05 m) and achieved an average velocity of 1,160 feet per second (353.6 m/s) and an average penetration depth of 11.375 inches (28.9 cm). Both the velocity and the depth of penetration of the bullets of the invention compare very favorably to standard lead core projectiles. Other properties including upset diameter and weight retention were comparable to that of conventional lead projectiles. Example 4 9 millimeter Luger copper jacketed soft point projectiles manufactured with an essentially pure tin core, as described in Example 1, were loaded in standard 9 millimeter shells as described in Example 3 and compared to a 9 millimeter Luger zinc core bullet of the type disclosed in United States Patent No. 5,679,920. The average weight of the bullet of the invention was 105 grains (6.80 g) and of the zinc base bullet, 100 grains (6.48 g). When fired at a temperature of 70°F (21°C), the bullets of the invention had an average velocity of between 1,155 and 1,245 feet per second (352 and 379 m/s). The zinc core bullets had an average weight of between 1,226 and 1,252 feet per second (374 and 382 m/s). The accuracy of the bullets was evaluated. Five shots were fired from each of three different 9 millimeter Luger test barrels at a target 50 yards (45.7 m) away. Each test was repeated five times and the extreme spread, in inches, between each set of 5 shots recorded in Table 2. The extremely high accuracy of the projectiles of the invention approach match grade. TABLE 2 Tin Core 9mm Jacketed Soft Point Test # BBL #1 BBL #2 BBL #3 1 0.94 (2.39 cm) 1.22 (3.10 cm) 1.02 (2.59 cm) 2 2.29 (5.82 cm) 1.96 (4.98 cm) 0.59 (1.50 cm) 3 1.40 (3.56 cm) 0.92 (2.34 cm) 0.87 (2.21 cm) 4 1.40 (3.56 cm) 1.64 (4.17 cm) 0.72 (1.83 cm) 5 0.88 (2.24 cm) 0.74 (1.88 cm) 0.84 (2.13 cm) Average 1.38 (3.51 cm) 1.30 (3.30 cm) 0.81 (2.06 cm) Zinc core 9 mm Jacketed Soft Point Test # BBL #1 BBL #2 BBL #3 1 2.41 (6.12 cm) 1.93 (4.90 cm) 0.98 (2.49 cm) 2 2.34 (5.94 cm) 1.30 (3.30 cm) 1.55 (3.94 cm) 3 1.30 (3.30 cm) 1.23 (3.12 cm) 1.72 (4.37 cm) 4 0.82 (2.08 cm) 1.38 (3.51 cm) 1.06 (2.69 cm) 5 1.52 (3.86 cm) 1.34 (3.40 cm) 1.41 (3.58 cm) Average 1.68 (4.27 cm) 1.44 (3.66 cm) 1.34 (3.40 cm) BBL = 9 millimeter Luger test barrel. The ricochet potential was evaluated by firing five essentially pure tin core projectiles and five zinc core projectiles at a one quarter inch soft (0.635 cm) steel plate target having a Brinnel hardness of between 55 and 60 HB. The target was placed 50 feet (15.24 m) in front of a 9 millimeter Luger test barrel at a zero degree offset angle. Table 3 records the results of impact between projectile and target. TABLE 3 * BJ = Bullet Jacket. * ' - Distance in feet. It is apparent that there has been provided in accordance with the present invention a lead-free projectile that fully satisfies the objects, means and advantages set forth hereinabove. While the invention has been described in combination with embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

Claims: I Claim: 1. A lead-free projectile (10, 30, 40, 42, 44), characterized by: a metallic jacket (12, 46) having an outer surface (18) defining an aerodynamic profile and an inner surface (14) defining at least one cavity; and said at least one cavity being filled with essentially pure tin (16) having a yield strength of less than 20 MPa. 2. A lead-free projectile (10, 40, 42), characterized by a body (16) of essentially pure tin having a yield strength of less than 20 MPa and formed to an aerodynamic profile. 3. The lead- free projectile of any of claims 1 or 2 characterized in that said essentially pure tin has a maximum of 0.5%, by weight, of total alloying additions and a maximum of 0.25%, by weight, of any one alloying addition. 4. The lead- free projectile of claim 2 characterized in that essentially pure tin has a maximum of 0.2%, by weight, of total alloying additions and a maximum of 0.1%, by weight, of any one alloying addition. 5. The lead-free projectile of claim 4 characterized in that a maximum zinc content of said essentially pure tin is less than 0.005%, by weight. 6. The lead free projectile of claim 5 characterized in that said essentially pure tin contains at least 99.85%, by weight, of tin and, by weight, a maximum of 0.04% antimony, a maximum of 0.05% arsenic, a maximum of 0.030% bismuth, a maximum of 0.001% cadmium, a maximum of 0.04% copper, a maximum of 0.015% iron, a maximum of 0.05% lead, a maximum of 0.01 % sulfur, and a maximum of 0.01% (nickel + cobalt). 7. A lead-free projectile (10, 30, 40, 42, 44), characterized by: a metallic jacket (12, 46) having an outer surface (18) defining an aerodynamic profile and an inner surface (14) defining at least one cavity; and said at least one cavity being filled with a tin base alloy (16) containing magnesium and having a yield strength of less than 20 MPa. 8. The lead- free projectile of claim 7 characterized in that said magnesium is present in an amount of from about 0.5% to 5%, by weight, and other alloying additions are present in a total amount of less than 0.5%, by weight. 9. The lead-free projectile of any of claims 1, 7 or 8 characterized in that said metallic jacket is formed from a metal selected from the group consisting of copper, aluminum, copper alloys, aluminum alloys and steel. 10. The lead-free projectile of claim 9 characterized in that said metallic jacket is formed from a copper-zinc alloy. 11. The lead- free projectile of claim 9 characterized in that said projectile is effective to be fired from a pistol. 12. The lead-free projectile of claim 9 characterized in that said projectile is effective to be fired from a rifle. 13. The lead-free projectile of claim 9 characterized in that said metallic jacket has a centrally disposed partition portion separating a rear cavity and a forward cavity with essentially pure tin being contained within both said rear cavity and said forward cavity. 14. The lead-free projectile of any of claims 1, 7 or 8 further characterized by at least one cup-shaped insert disposed in said at least one cavity between said essentially pure tin and said nose portion.

Inventors: BUENEMANN MORRIS C JR, ENLOW KEITH E, BUENEMANN, MORRIS, C., JR., ENLOW, KEITH, E.
Applicants: OLIN CORP, OLIN CORPORATION
Application year: 1998
Main classification: F42B12
IPC codes: F42B12, F42B30