US3049998A - Ammunition - Google Patents

Description

Aug. 21, 1962 R. A. BROWN 3,049,998

AMMUNITION I Filed Sept. 14, 1956 INVENTOR. ROBERT A. BROWN United States PatentOfiFice 3,049,998 Patented Aug. 21, 1962 3,049,998 AMMUNITION Robert A. Brown, Milford, Conn, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Sept. 14, 1956, Ser. No. 611,408 1 Claim. (Cl. 10238) This invention relates to ammunition particularly intended for use in a light weight, high velocity military pistol of superior effectiveness. More specifically, this invention relates to a cartridge incorporating a bullet having among its desirable characteristics a shape such as to facilitate the cartridge loading operation and improve the interior and external ballistics of that cartridge. This invention also includes the methods and procedures for producing the particular bullet.

In the design of a new military pistol, .a need arose for a bullet of lesser sectional density than that of the usual combination of a lead core and gilding metal jacket, and one of the military requirements for the new cartridge was that at least the core and preferably all of the bullet should be formed of a ferrous metal.

In addition to all the usual factors of aerodynamic design, bullet launch, and bullet spin that influence the accuracy of all bullets, ferrous metal bullets are sensitive to such factors as contact area with the barrel, hardness of the bullet, and treatment of the bullets surface. I have determined that an ideal ferrous metal bullet should have the following general characteristics:

(1) Most of the bullet should have a diameter appreciably smaller than the bore of the gun through which it is to be fired. Only sufiicient bullet material should contact the barrel to maintain the bullets alignment during its passage through the bore. These supporting rifling bands should be as narrow as practicable and be followed by relieved portions that are several times the length of the preceding band. The bands should be located near the ends of the bullet to lengthen the alignment base of the latter.

(2) The bullet material should be of such type that heat or other treatment will bring its Diamond Pyramid Hardness kg. load) below 100. Values in the 70s or lower are even better. There appears to be good correlation between iron bullet hardness and accuracy. The bullet material must be so selected and so handled that its hardness does not tend to increase with time.

(3) Since an iron bullet is to be fired through a barrel of similar material, we encounter an unfavorable bearing situation. We have two similar materials rubbing together and they tend to gall or seize instead of sliding easily over each other. The introduction of a dissimilar material into this hearing is practically a necessity.

(4) Despite its many useful characteristics, iron is subject to surface attack by the atmosphere and must be protected against such contact if it is to be a useful service material. For instance, Johnson, Godfrey and Bisson report in their paper on Friction of Solid Films on Steel at High Sliding Velocities that the presence of ferric oxide on steel is detrimental to friction and wear of the surfaces. Poor friction characteristics lead to high contact temperatures and the momentary welding that is detrimental to barrel wear .and bullet accuracy. Therefore a corrosion-resistant finish must be supplied.

It was the particular object of this invention to produce a cartridge loaded with a bullet having these characteristics.

The exact nature of the invention as well as other objects and advantages thereof will become more apparent from consideration of the following specification referring to the attached drawing, in which:

The single FIGURE is a longitudinal sectional view to a greatly enlarged scale showing a cartridge embodying the invention.

Referring to the drawing by characters of reference, it will be seen that there is illustrated a cartridge including a cartridge case 1, a bullet 2, a primer 3, and a charge 4 of propellent powder. The cartridge case, primer, and propellent are of conventional form, although the engagement between the cartridge case and bullet is not of the usual form.

The bullet 2 is preferably formed of Armco ingot iron to secure the desired metallurgical characteristics which will be further discussed and is shaped to define three bearing bands on its bore engaging surface.

Remembering the enumeration appearing above of the desired general characteristics of such a bullet, the reason for the size and location of the bullet bearing bands becomes comparatively self-evident. Referring to the drawing, it will be noted that the bearing band 5 adjacent the nose of the bullet is broad for strength but its diameter is kept close to bore size to reduce to a minimum the friction with the lands of the rifle in the bore. This bourrelet serves to maintain the fore portion of the bullet in accurate axial alignment with the bore of the barrel.

The second band 6 and the third band 7 are comparatively short in length and of suflicient length and of suifieient diameter to be engraved by the lands of the rifting and to fill the grooves of the barrel. This engagement seals in the propellent gases and imparts the stabilizing spin to the bullet as it is propelled through the barrel. The second hand 6 is located so that it just closes the mouth of the case 1 when seated to the proper depth. In conjunction with the rear band 7, it also serves to insure axial alignment between the bullet 2 and the case 1 of the loaded round. Ample clearance is provided hehind each of bands 6 and 7 to accommodate metal dragged rearwardly by the lands of the rifling to be deposited in the nearest unoccupied space. Logic indicated that both the displaced metal and the lands of the rifling would be under high pressure until this had been accomplished.

The remedy for this situation was twofold. First, the total length of each bearing band was reduced to the minimum necessary to spin the bullet under operating conditions. Second, this band length was so distributed that displaced metal need flow a minimum distance before dropping into a relief area and reducing the bullet barrel force.

The rear band 7 has been given a taper 8 originating at the heel of the bullet 2 and terminating in a sharp edge at the forward side of the band '7. The function of the sharp-edged band 7 is to form a seal for the powder chamber as well as to align the bullet in the case.

The taper heel 8 makes it possibleto seat bullets in cases without using a mouth opening punch during the loading operation. Since the case mouth is not opened prior to bullet seating, there is no need to crimp the case mouth after bullet seating, thus eliminating two stations in the loading operation. The rear band entering the case mouth stretches the case slightly and the elastic recovery thereof beyond the forward sharp edge on the band 7 and between this band and the second band 6 serves to lock the bullet to the case in such a way that bullet setback through the shocks and impacts of feeding in an autoloading pistol is only about 0.002" per cycle of operation, which is less than that usually experienced with conventionally seated lead-gilding metal bullets.

An ogival nose of about 0.8 caliber radius coming to a small point was selected as a compromise to secure the best all-around performance, taking into account such factors as the necessity to feed through a firearm characterized by an abrupt loading ramp, wounding efiiciency, and armor penetrating efficiency.

Armco ingot iron of the types disclosed in Handbook of Trade Names by Zimmerman and Levine was selected as the bullet material for several reasons. First, its low carbon content makes it less subject to atmospheric corrosion than a low carbon steel such as the SAE #1113 listed in yearly SAE Handbooks free machining steel with its 13 points of carbon. Two, although its Diamond Pyramid Hardness in the a-s-drawn state is the same as SAE #1113 steel, it was found that a decarburizing heat treatment in either hydrogen or dissociated ammonia softened Armco iron to the region of 70-80 kg./sq. mm. (D.P.H.), while SAE #1113 could not be brought below a D.P.H. of 1-15 kg./sq. mm. Furthermore, test pieces have indicated that A-rmco iron will retaint its soft skin for as long as 19 months if it is not cold worked during the period. Here is a material than can be made comparatively soft and which appears to retain this softness for an appreciable time.

The production of a bullet of this configuration from a material such as Armco ingot iron is not, however, free from all problems. In general, the procedure is to machine to exact tolerances, then decarburize to maximum softness and avoid subsequent working which could cause strain hardening. These steps may be followed by measures to prevent corrosion and to provide lubrication.

In regard to machining to exact tolerances, it will be noted that the selected bullet design was provided with three diameters, the bou-rrelet 5, the two bands 6 and 7, and the intermediate relief sections which clear the barrel entirely. This practically limits production methods to the method of turning and, consequently, only the sections of largest diameter, the rifling bands 6 and 7, can be sized tov exact diameters by passing the piece longitudinally through a conventional sizing die. The other diameters require closer control over" machining tolerances than can be achieved by conventional screw machine tooling. It was found to be possible to machine to the desired tolerance by fairly conventional screw machine techniques if the blank stock was centerless ground to .0001" tolerance and all turning done as in certain Swiss automatic machines by tools mounted very close to aprecision collet through which the blank stock was fed.

A more practical solution, however, was the use of a shaving tool as a second operation on a conventional screw machine. A first and conventional turning operation shaped the workpiece to within .00 of its final size prior to the shaving operation.

A shaving tool is similar in appearance to a heavy snap gauge that is allowed to float on a pin parallel to the workpiece. One anvil of the gauge is a tool bit shaped in the contour of the piece to be shaved while the second anvil is a free running roller. As this tool advances upon the work, the roller passes across the top side of the workpiece while its opposite member, the shaving bit, passes beneath the work as would be done in the action of snap gaging the diameter of the work. As the bit bears against the work, it takes a shaving out until the tool can pass completely past the diameter of the work, after which the tool is withdrawn and the workpiece cut off from the stock. In effect, the operation is one of shaving to gage size simultaneously with the gaging operation.

it should be pointed out, however, that the use of shaving tools is not the answer to the entire problem. To obtain good work, the screw machine itself must be in firstclass condition and its collet bearings must be true and properly fitted. With all these precautions, a check of the bourrelet diameter of 100 consecutive pieces showed that their range of diameters was 0.0005" and that 90% of the pieces were within a range of 0.0003".

Heat treatment, previously referred to, consists in decarburization of the bullet by heating in hydrogen or dissociated ammonia. For example, decar burization in dissociated ammonia for two hours at 1700 F. drops the: Diamond Pyramid Hardness of Armco ingot iron from. 170-180 kg./sq. to about 80. Since a hard bullet tends to localized melting and occasional welding to the: gun bairel, it is highly inaccurate and tends to greatly reduce barrel life. It is therefore apparent that the softest condition which can be created is the most desirable.

To create a better bearing condition, it is, as previously noted, desirable to introduce a dissimilar metal into the: bearing area between the iron bullet and the steel barrel. Nickel, if adequately lubricated, has been established to be a satisfactory bearing material in this application, but it must be applied by methods which do not tend to cause hydrogen embrittlement of the bullet per se, as is encountered in electroplating the nickel coating. Of the several possibilities for hydrogen-free plating, the most success was found in the use of the Electroless plating process which forms the subject of US. Patent No. 2,5 32,- 283, issuing from work done at the National Bureau of Standards. In following this process, nickel plates out equally on all surfaces touched by the solution and with out the evolution of any of the embrittling hydrogen. Armco iron test pieces nickel plated in this way showed a 50% resistance to standard salt spray corrosion tests of about 160 minutes as compared to 22 minutes for the unplated material. Nickel is not well regarded by ballisticians as a bullet jacket material and, as suspected, these bullets shot poorly until they were given the special lubri' cating treatments discussed below.

One highly effective lubricant was- Surfkote H-205, manufactured by the Hohman Plating and Manufacturing Company, Inc., of Dayton, Ohio. For this operationtheir formula H-205 appears to be the best material since it has the highest operating temperature which is listed as 950 F. This material is believed to be an emulsion of molybdenum disulphide in a suitable lacquer-like carrier and best results were obtained by thinning this emulsion with toluene and spraying it with an external mix spray gun uponbullets pre-warmed to about to F. For uniform application, the bullets should be rotated, as by spinning them on a carrier analogous to a magnetic chuck, as they pass through the field of the spray gun. After air-drying of the sprayed film the bullets are baked for two hours at 600 F.

To effect a further improvement in bullet lubrication and to assist in sealing the mouth of the cartridge case, the cartridges are dipped nose-down, to a depth just over the mouth of the case, into a bath of molten lubricant which is kept between 210 and 240 F. and held there for about 60 seconds. The cartridges are then withdrawn and the drop of lubricant which collects on the nose of the bullet is touched off on a cloth pad and the cartridges allowed to cool bullet-up. This places a lubrieating film over the entire bullet and deposits at fillet of wax at the case mouth to insure moisture-proofing of the powder charge and primer.

As a final lubricant, it was determined that it would be des rable to use one of the Dow Corning Silicone fluids designed specifically -to provide lubricity for steel-to-steel contacts at high temperatures. One such lubricant was known as Dow Corning Silicone Fluid XF-4050 and was intended for an aircraft gas turbine lubricant. This fluid, however, has a viscosity at room temperature about the same as that of a light machine oil which requires that it be blended about half and half with a micro crystalline wax such as Ozokerite to yield a practical wax bullet lubricant which will be retained on the bullet. Such a lubricant blend is disclosed and claimed in the pending application of OConnor and Schilling, UgS. Serial Number 532,124, filed September 1, 1955, and entitled, Projectile Lubrication, to which reference may be had for further details.

By the use of the combination of Electroless nickel plate, Surfkote spray, and silicone-wax lubricant, it is believed that the problems of lubrication and corrosion prevention have been satisfactorily solved without hydrogen embrittlement or other deleterious effects upon the bullet or' its performance characteristics.

Although the invention has been quite specifically described above, it will be realized that there are certain equivalent constructions and procedures coming within the scope of the appended claim to which reference should be made for an exact definition of the limits upon the scope of the invention.

I claim:

Ammunition for a rifled gun comprising a cylindrical cartridge case closed at one end and open at the other end, said cartridge case adapted to fit in the gun barrel, a propellant material within the cartridge case, a bullet adapted to be seated above the propellant material in said cartridge case, said bullet having an ogive shaped nose extending beyond the open end of the cartridge case, a bourrelet at the base of the nose to maintain the bullet in axial alignment with the barrel of the gun, said bullet having a tapered heel portion with a minor diameter at the base less than the inside diameter of the cartridge case and a major diameter greater than the normal inside diameter of the cartridge case, said major diameter portion constituting a first rifling band and adapted to spread the open end of the cartridge case when inserted therein and to maintain said bullet securely Within the cartridge case, a second rifling band between the bourrelet and the first named rifting band and of the same diameter as the first rifling band, said second band being embraced by the open end of the cartridge case which open end is crimped over the second band to seal the said bullet within the case, the body portion of the bullet between said bands and between said bourrelet and said second band being of a reduced diameter to form annular grooves therebetween, said annular grooves being of a greater longitudinal length than the bands and the bourrelet and adapted to form between the bands and between the hourrelet and the second band closed compartments with the cartridge case and the gun barrel to contain combustion gases and displaced metal from the rifling when the ammunition is discharged.

References Cited in the file of this patent UNITED STATES PATENTS 270,101 Nordenfelt Ian. 2, 1883 450,623 Kauderer Apr. 21, 1891 703,879 Wratzke July 1, 1902 1,189,011 Smith June 27, 1916 2,103,155 Foulke Dec. 21, 1937 2,120,913 Studler Jan. 14,- 1938 2,188,465 Perrin Jan. 1940 2,532,283 Brenner Dec. 5, 1950 FOREIGN PATENTS 13,934 Great Britain 1852 20,970 Great Britain 1889 2,985 Great Britain 1907 438,311 Great Britain Nov. 14, 1935

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