Patent Publication Number: US-6209459-B1

Title: Method for etching characters on bullets and bullets made by the method

Description:
FIELD OF THE INVENTION 
     The present invention concerns a method for marking a bullet with characters and bullets marked according to the method. 
     BACKGROUND OF THE INVENTION 
     Ammunition bullets are characterized by, among other things, caliber and weight. Caliber represents the diameter of the bullet, while weight represents the mass of the bullet. Bullet mass is commonly designated in terms of avoirdupois grain weight throughout the United States. 
     The flight trajectory and terminal performance of a bullet depend heavily upon the caliber and the weight of the bullet. For example, with other ballistic variables being equivalent, a bullet with a heavier weight sustains its flight velocity better than a lighter weight bullet. The heavy weight bullet, usually launched at a lower initial velocity, drops further from the line of sight than a lighter bullet when fired at the same target. This requires aiming adjustments by the shooter when using ammunition with different weight bullets. 
     Heavy weight bullets typically penetrate deeper upon terminal impact than lighter bullets, which partially compensates for their lower velocities. Other technical advantages and disadvantages of light or heavy bullets are well known to experienced marksmen. 
     Marksmen therefore want to know the weight of the bullets in the cartridges they intend to shoot. Differences in bullet weights often are not apparent simply by viewing or handling loaded cartridges. Bullets weights for a common cartridge in its various loadings might vary between 100 and 125 grains. A 25 grain (0.057 ounce) difference is not substantial enough to allow the shooter to quickly or reliably differentiate between two cartridges while holding one of each bullet weight type. Visual determination of bullet weight is not practical because a significant portion of a bullet in a cartridge is obscured by the cartridge casing. Other important bullet characteristics such as construction materials and design features also may not be visibly apparent after the bullet is assembled into a finished cartridge. 
     Most manufacturers mark ammunition packaging with some indication of bullet weight and perhaps other bullet characteristics. However, packaging markings are ineffective once the bullet has been removed from the package. Moreover, spent casings of cartridges often are reloaded with new cartridge components and the resulting reloads do not necessarily incorporate the proper information to identify the bullet loaded therein. 
     Some inventions are known whereby bullets convey information. Marking bullets with a system of bands or grooves to indicate bullet characteristics is described in, for example, U.S. Pat. Nos. 1,632,156 and 1,650,908. But, in each situation these marking schemes require marksmen to memorize several different configurations of bands and the corresponding bullet characteristics. Further, such marking systems are not generally known by the shooting public. 
     U.S. Pat. Nos. 1,887,324, 4,150,624 and 5,485,789 describe bullets having identifiers embedded therein. These inventions offer no help to marksmen because the information is stored inside the bullet and is not visible. Such information generally is of a type not intended for marksmen anyway as such information is usually provided for forensic purposes. 
     SUMMARY OF THE INVENTION 
     Based on the above, it is apparent that a need exists for a method for marking bullets so that marksmen can quickly and reliably identify the bullet weight and type when loaded in a cartridge. The present invention addresses this need. 
     One embodiment of the present method for etching a character or characters onto a bullet comprises first providing a bullet having a coating on at least a portion thereof. The coating typically has a surface appearance that contrasts with a portion of the bullet that underlies the coating. One or more characters are then etched through the coating. For example, a character or characters may be etched through the coating to reveal the underlying bullet substratum. 
     The etching step can be performed mechanically, chemically or with a localized energy source such as an electron beam or a laser. Examples of lasers having sufficient power for commercial production of large quantities of etched bullets according to the present method include, without limitation, YAG and CO 2  lasers. Alternatively, the etching step can be performed mechanically, such as by applying an abrasive to the coating, or by stamping a dot matrix pattern through the coating to form a character or characters. 
     Functionally, the coating acts as a contrast agent, but it also can have other desired technical functions when applied to a bullet, such as acting as a lubricant. Coatings currently considered useful for practicing the present method are selected from the group consisting of molybdenum disulfide, tin, copper, metallic oxides, zinc, nickel, silicon, organic resins, paints, stains, aluminum, gold, silver, and mixtures and alloys thereof. Molybdenum disulfide is a currently preferred coating. 
     The present invention is particularly useful for etching bullet weight and type numerals onto a bullet. The method involves providing a cartridge comprising a bullet and a casing. The outer surface of the bullet is then coated with molybdenum disulfide. A laser is then focused on the coating in a desired pattern to remove a portion of the coating corresponding to the pattern. Contrast between the coating and the exposed substratum of the bullet helps marksmen see the bullet weight and type characters. These characters are located on the bullet in a position that they are easily seen even after the bullet is loaded in the cartridge casing. 
     The present invention also is directed to bullets etched by the method briefly described above. One embodiment of an etched bullet comprises a core and an jacket. A coating is applied over at least a portion of the plating, and characters are etched through the coating to reveal an outer surface of the plating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an etched bullet made in accordance with the present invention. 
     FIG. 2 is an enlarged sectional view of the embodiment of FIG. 1, taken along line  2 — 2 . 
     FIG. 3 is an enlarged sectional view of an alternative embodiment of the bullet illustrated in FIG.  1 . 
     FIG. 4 is an enlarged sectional view of an alternative embodiment of the bullet illustrated in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A. Definitions 
     The following definitions are provided solely for the convenience of the reader. The definitions should not be construed to limit the terms defined to a scope narrower than would be known to a person of ordinary skill in the art. 
     Ammunition: Multiple cartridge for firearms, guns or cannons. 
     Cartridge: A single, complete, self-contained unit for use in firearms. It incorporates a shellcase, bullet, propellant powder and primer. 
     Bullet: The projectile intended to be expelled from a firearm upon discharge. 
     Loading: The particular type, size quantity, or combination of cartridge components assembled for a specific purpose. 
     Propellant: The cartridge energy source. Also referred to as “gun powder” or “powder.” 
     Primer: The cartridge ignition device, usually activated by firearm imposed mechanical Ipercussion or electrical discharge. 
     Shellcase: A generally tubular container intended to contain and orient the other firearm cartridge components. Also referred to as “case” and “casing.” 
     B. Bullet Composition and Structure 
     Referring to FIG. 1, cartridge  10  consists of a bullet  12  (FIG.  2 ),  12 ′ (FIG. 3) or  12 ″ (FIG. 4) and a casing  14 . Elongated casing  14  has an open end  16  and a closed end  18 . Open end  16  is shaped to receive bullet  12 ,  12 ′ or  12 ″. Visible ogive portion  20  of bullet  12 ,  12 ′ or  12 ″ (“ogive” refers to the cylindrical, tapered or curved, forward part of the bullet) extends outwardly from casing  14 . 
     Bullets can have various compositions, and can be jacketed with various materials, with copper-alloy jacketed bullets being but one example. Bullets also can be formed from a solid piece of material, with copper being one example. The present invention can be practiced with all such bullets, as will be appreciated by a person of ordinary skill in the art. 
     Solely to illustrate the invention, FIG. 2 shows an embodiment of a bullet  12  that can be etched in accordance with the present invention. Bullet  12  includes a core  22 , preferably a lead-alloy, a jacket  24 , and a coating  26 . Jacket  24  typically comprises a metal or alloy, such as copper, brass, nickel or zinc. Jacket  24  may substantially completely or completely surround the core  22 . 
     FIG. 3 illustrates bullet  12 ′. Bullet  12 ′ consists entirely of lead, copper, brass or other metallic alloys or compositions used for making bullets. FIG. 3 also shows that the bullet  12 ′ includes a coating  26 . 
     FIG. 4 illustrates bullet  12 ″. Bullet  12 ″ includes a core  22 , such as a lead-alloy core, and a jacket  24 . FIG. 4 also shows that the bullet  12 ″ can include plural coatings, such as coatings  26  and  28 . 
     Usually, but not necessarily, bullets  12 ,  12 ′ or  12 ″ are marked with characters rather than the casing  14 . One reason for this is that casing  14  may be reloaded with a bullet having a different weight or type than that of the original, which might render inaccurate the initial information stated on casing  14 . 
     C. Coatings and Methods of Coating Bullets 
     A first coating  26  is disposed over at least a portion of bullet  12  or  12 ′. FIG. 4 illustrates that bullet  12 ″ can have plural coatings, with the illustrated embodiment having an outside coating  26  and an inside coating  28 . In a preferred embodiment, an underlying portion of bullet  12  or  12 ″ that underlies coating  26  or  28  is a portion of jacket  24 . One consideration for selecting a material for coating  26  and  28  is how well it contrasts with jacket  24 . A currently preferred embodiment of bullet  12  uses a dark coating  26 , which contrasts well with the metallic color of the copper or brass jacket  24 . 
     Coating  26  also preferably functions as a lubricant. A lubricant on bullet  12 ,  12 ′ or  12 ″ decreases wear to the bore of the gun barrel. This increases the useful lifetime of the barrel. 
     In a preferred embodiment, coating  26  or coating  28  comprises molybdenum disulfide (MoS 2 ). Molybdenum disulfide is used because (1) it is dark in color and (2) it functions as a lubricant. Alternatively, the coating  26  or  28  may comprise tin, which also is a lubricant. In yet another embodiment, coating  26  or  28  consists of a metallic oxide, such as copper oxide (CuO). In still another embodiment, jacket  24  is steel, and coating  26  or  28  is copper. Thus, without limitation, coatings  26  and  28  currently considered useful for practicing the present method may be selected, without limitation, from the group consisting of molybdenum disulfide, tin, copper, metallic oxides, zinc, nickel, silicon, organic resins, paints, stains, aluminum, gold, silver, and mixtures and alloys thereof. 
     If used, coating  26  is applied over jacket  24 , or solid bullet material  30 , or second coating  28 , in a layer sufficiently thin so that it does not substantially alter the aerodynamic, mass, mechanical or other desired characteristics of bullet  12 ,  12 ′ or  12 ″. The thickness of coating  26  and  28  typically ranges between an immeasurable thickness where the coating material penetrates the surface of the bullet  12 ,  12 ′ or  12 ″ to a thickness of 0.001 inch. However, coatings  26  and  28  may be thicker if the mass, mechanical and aerodynamic properties of coating  26  are taken into account when it is applied. 
     A pattern  32  is etched onto the visible portion  20  of bullet  12 ,  12 ′ or  12 ″ and extends sufficiently through coating  26  to reveal jacket  24 , or bullet material  30 , or second coating  28 . In a preferred embodiment shown in FIG. 1, etched pattern  32  states the weight in grains (i.e., 150) of the bullet and the type of bullet (i.e., Spitzer), (SP). In addition to numerals and letters, other markings such as trademarks, logos, symbols, designs, indicia, statements concerning other characteristics of the bullet, etc., may be etched onto bullets. Numerals, words, trademarks, logos, symbols, patterns, designs, indicia, statements concerning other characteristics of the bullet, and all other manner of markings, are collectively referred to herein as characters. Individual characters of pattern  32  etched onto bullets are easily read because of the contrast between the surface appearance of the coating  26  and that of the substratum jacket  24 , the contrast between coatings  26  and bullet material  30 , or the contrast between coating  26  and coating  28 . 
     The method for manufacturing bullets, including the method for applying the jacket  24  around the core  22 , is known to those of ordinary skill in the ammunition industry. Any previously known method for manufacturing bullets to be marked according to the present invention is acceptable. As stated above, the entire body of the bullet  12 ′ may consist of a single material, such as copper or lead alloy bullet materials  30 . In another method, jacket  24  is around the core  22 . 
     Once the bullet  12  or  12 ′ is manufactured, it is then coated with coating  26 . In a preferred embodiment, bullet  12  with an electroplated jacket  24  is coated with MoS 2 , as stated above. The currently preferred method for coating articles with MoS 2  is described in U.S. patent application Ser. No. 60/049,692, which is incorporated herein by reference. 
     Alternatively, bullet  12 ,  12 ′ or  12 ″ may be coated with an oxide by oxidizing those materials forming the external surface of the bullet, such as jacket  24 , solid core  30 , or coating  28 . The oxide coating is produced by exposing bullet  12 ,  12 ′ or  12 ″ to an oxidizing agent for a sufficient period to oxidize the surface of the bullets. The type of oxidizing agents and time of exposure to these agents vary for given jacket materials. A system is used that provides adequate contrast between the oxide finish and the underlying jacket. 
     In another embodiment, one metal or alloy core  30  or jacket  24  may be coated with another metal or metal alloy coating  26  or  28 . For example, copper may be coated over steel or tin over copper. This may be accomplished by electroplating a thin layer of metal on the underlying jacket, or peening powdered metal into the surface of the underlying jacket. 
     An additional embodiment (FIG. 4) combines one (or more) thin inside coating layers  28  of metals superposed over jacket  24  or core  30  and possibly an outer layer  26  of a lubricant coating. With the layers  26  and  28  being in visual contrast with one another, different colors can be exposed by varying the depths of coating removal. For example, a copper jacket can have a thin nickel coating with a black MoS 2  coating over the nickel. 
     D. Etching Bullets 
     After bullet  12 ,  12 ′ or  12 ″ is coated, coating  26  and/or  28  is then etched. The etching preferably extends through the coating  26  but not substantially into the jacket  24  or base material  30 . Any etching method or device that will etch the desired patterns with the requisite accuracy and predictability to form legible characters into or through the coating  26  and/or  28  can be used to practice the present invention. For example, etching can be accomplished using a chemical etchant, such as acids, alkalis, or organic solvents, dependent on the coating material  26  and/or  28  to be etched. Another method for etching would be to use an electron beam device. The etching step also can be accomplished using an abrasive media device or cutter designed for etching. All etching devices are collectively referred to herein as an “etcher” or as “etchers”. Etching also can be accomplished using any combination of these methods. 
     A preferred etcher is a laser in which energy is focused on, for example, bullet  12 ,  12 ′ or  12 ″ in a pattern designed to melt, oxidize, vaporize, or displace the coating  26  and/or  28  in its path corresponding to a desired pattern  32 . Any of several well-known types of lasers can perform the laser etching operation. For mass production, the etching step should be performed quickly. One factor to consider for determining whether a particular laser is appropriate for etching bullets is the power required for a desired etched bullet output. It currently is known that a YAG or CO 2  laser would be useful for commercial production of etched bullets because of their high energy output. 
     The time necessary to etch a bullet varies depending on a number of factors, including the size and intricacy of the pattern being etched, the thickness of the coating  26  or  28 , the location of the etched pattern on the bullet and the laser used. Typically, however, the etching time is between a fraction of a second and three seconds. These etching times are short enough to keep pace with the rest of the production steps used for manufacturing bullets. 
     Any of several methods may be used to position bullets to be etched by an etcher. In a preferred laser-etching embodiment, bullets,  12 ,  12 ′ or  12 ″ are placed in jigs arranged on a plate under the laser. This method allows a large quantity of bullets  12 ,  12 ′ or  12 ″ to be processed quickly and inexpensively. In an alternative embodiment, bullets  12 ,  12 ′ or  12 ″ are placed individually into a rotating jig. The jig then turns bullets  12 ,  12 ′ or  12 ″ as the laser etches them. The rotating jig allows the laser to etch around the entire circumference of bullets  12 ,  12 ′ or  12 ″, while the plate may allow the laser to etch only limited areas of bullets  12 ,  12 ′ or  12 ″. 
     In another embodiment for etching bullets using an etcher according to the present invention, coating  26  and/or  28  is glass bead or sand blasted away to reveal an underlying portion of the bullet  12 ,  12 ′ or  12 ″. Such abrasive techniques for etching articles other than bullets are known. One such method is practiced commercially by Marble Marking Products of Pittsburgh, Pa. 
     Still another alternative etching method comprises stamping dots into the coating  26  and/or  28 . In this embodiment, the stamp penetrates through coating  26  and/or  28  to reveal the underlying material. A dot matrix system, as incorporated on some printers, form the desired insignia. Suitable stamping methods also are known, such as the processes practiced by Microdot Marking Systems of Cleveland, Ohio. 
     In another embodiment, neither bullet  12 ,  12 ′ or  12 ″ are coated with coating  26 . In this embodiment a pattern is etched directly into bullet  12 ,  12 ′ or  12 ″ to form a recognizable character or characters, such as the characters described above, particularly bullet weight. The same types of etching methods may be used for this embodiment as described for the previous embodiments. 
     Although the invention is described herein with reference to certain preferred embodiments, one of ordinary skill in the art will appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the invention.