US3460478A

US3460478A - Projectile with sintered metal driving band

Info

Publication number: US3460478A
Application number: US725244*A
Authority: US
Inventors: Gottfried Ormanns
Original assignee: Rheinmetall GmbH
Current assignee: Rheinmetall Industrie AG
Priority date: 1964-10-24
Filing date: 1968-02-06
Publication date: 1969-08-12
Anticipated expiration: 1986-08-12
Also published as: ES318813A1; NO115724B; CH444717A; DE1243055B; NL6513597A; DK125558B; BE671271A; GB1092318A

Description

A g- 6 G. ORMYANNS 3,460,478

PROJECTI LE WITH SINTERED METAL DRIVING BAND Fil ed'Feb 'e, 1968' 2 Sheets-Sheet 1 G. ORMANNS V PROJECTILE. WITH SLNTERED METAL DRIVING BAND Filed Feb. 6, 1968 Aug. 12,1969

2 Sheets-Sheet 2 United States Patent Int. (:1. F42b 31/00 US. Cl. 102-93 1 Claim ABSTRACT OF THE DISCLOSURE A projectile having sintered metal driving band disposed in an external annular groove in the jacket wherein the possibility of fracture and crumbling of the driving band is reduced while preferred ballistic characteristics for the projectile are retained by formation of the annular groove and driving band with surfaces such as that forces acting on the driving band upon firing of the projectile are restricted to compressive forces only.

This application is a continuation-in-part of a copending application filed Oct. 23, 1965, under Ser. No. 503,828, and entitled, Projecticle Having a Guide Ring, now abandoned.

It has long been known that the bore life of firearms such as artillery pieces may be extended by forming projectiles fired therein, such artillery shells, with a driving band fixed in an annular groove formed in the casing :or jacket of the projectile. Such driving bands, also known as guide or rifling rings, permit obtaining necessary sealing of the propelling gases within the bore of the firearm and transmittal of spinning forces to the projectile without requiring that the casing or jacket of the projectile be formed with sufiiciently large diameter to fully engage the lands and grooves of rifling in the barrel and thus reduce wear and erosion of the bore. In order to permit ready deformation of the driving band and thereby reduce the energy lost during engagement of the projectile with the rifling lands and grooves within a rifle barrel, while assuring that the other objectives for the driving band are met, such bands have long been made of solid bodies of ductile nonferrous metals such as copper, brass, or bronze.

In the history of projectile development, driving bands were initially placed at the extreme rearward portion of a projectile casing or body in order to facilitate assembly of the projectile by having the driving hand held in position by a threaded ring or in order to permit forming the projectile casing with a weakened rearward portion. The latter consideration was held to be particularly important in armor-piercing shells, where the driving band projecting outwardy beyond the principal diameter of the projectile casing caused difficulty in penetration of the projectile through armor plate.

In the more recent history of projectile development, it has been realized that placement of a driving band at the extreme rearward extremity of a projecticle detracts from the ballistic characteristics of the projectile, as rotational forces is applied to the projectile remote from the ballistic center thereof and leads to excession of the projectile during flight. Additionally, recent trends in the development of firearms and projectiles have been toward projectiles of smaller diameter fired at higher velocities and toward firearms capable of fast loading and rapid firing. In view of these trends, driving bands of ductile non- 3,460,478 Patented Aug. 12, 1969 ICC ferrous metals have become less satisfactory. While such solid bodies of ductile metals have adequate time to flow into the rifling grooves of a barrel when the operations of loading and velocities on firing are relatively slow, and since there is little or no resistance to such plastic deformation, pressures on the barrel from the projectile do not increase excessively. However, as the speed with which a projecticel traverses the bore is increased, ductile metals of the type heretofore used have insufficient time to flow into the grooves of the rifling and tremendous pressures are exerted on the barrel wall, thereby increasing fatigue and causing relatively early failure of the barrel. Sintered metallic driving bands, by way of constant with ductile meala bands, have a skeletal or porous structure, which permits the band to collapse or give away at the rifling lands, regardless of the velocity with which the projectile is fired. For this reason, pressures exerted on the barrel by the projectile are lower and improvements are realized in barrel life, obturation, range and accuracy for the given round of ammunition.

Sintered metal bands are, however, subject to certain deficiencies which did not appear in the earlier used ductile metal bands, resulting primarily from the very skeletal or porous structure of such sintered metals which provides the advantages leading to adoption of such driving bands. More particularly, while sintered metal structures will absorb compressive forces, as by collapse of the porous metal structure, such structures are somewhat friable and tend to crumble or fracture upon the exertion of tension froces on the metal body. Due to thislcharacteristic of sintered metal bodies, difliculties have been encountered in the a plication of driving bands made of sintered metal to projectiles intended to be fired at relatively high velocities. As best can be determined, tension forces on such bands arise largely as a result of couple forces or bending moments required in order to accommodate the resultant of the basic forces acting upon the driving band upon firing of the projectile. The principal forces believed to give rise to tension on the driving band, and thus believed to be responsible for crumbling and fracture of sintered metal driving bands, are the force acting longitudinally of the projectile and resulting from relative movement between the projectile and the barrel and the radially directed force resulting from rotation about longitudinal axis of the projectile.

In view of the above, it is an object of the present invention to provide a projectile including a sintered metal driving band disposed in an external annular groove in the jacket of the projectile wherein the formation of the external annular groove is such that the exertion of tension forces on the drive band upon firing of the projectile through a barrel is substantially avoided, and the driving band is thereby protected against fracture and crumbling due to the forces imposed thereon being restricted to compressive force alone. In realizing this object, the annular groove and driving band are so positioned relative to the jacket of the projectile as to facilitate obtaining satisfactory ballistic performance for the projectile. These advantageous characteristics for the projectile are obtained by forming the annular groove in a thick wall portion of the projectile jacket and in such relation to an adjacent thin wall portion of the jacket as to not reduce the strength of the thick wall portion of the jacket below that of the thin wall portion while placing the groove as closely as possible to the ballistic center of the projectile, and by forming the annular groove with a base wall directed substantially in the direction of the resultant of the two aforementioned forces acting on the driving band upon firing of the projectile.

Some of the objects and advantages of this invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which FIGURE 1 is a view of a portion of a projectile in accordance with the present invention in longitudinal sections showing the position of the external annular groove in the projectile jacket and the driving band as disposed in that groove;

FIGURE 2 is an elevation view, in section, of a driving band in accordance with the present invention prior to insertion thereof into the external annular groove in a projectile jacket;

FIGURE 3 is a diagram of the two aforementioned forces acting on a driving band during firing of a projectile; and

FIGURE 4 is an enlarged elevation view, in section, of the driving band and projectile jacket.

Referring now more particularly to the drawings, the left-hand portion of FIGURE 1 illustrates a projectile jacket having a thin Wall portion 1, enclosing a central cavity 12 which may receive a hardened core or a charge of explosive, and a thick wall portion 11 spaced rearwardly of the thin wall portion of the jacket. Formed in the thick wall portion 11 is an annular groove 2, shown in the right-hand portion of FIGURE 1 without a driving band installed therein and in the left-hand portion of FIGURE 1 with the driving band 3 disposed therein. The driving band 3, in accordance with the present invention, is a body of sintered metal such as iron, which may have lubricant forced into the pores thereof to aid in reducing friction as the projectile is fired through a rifled barrel.

In order to restrict the forces exerted upon the driving band 3 to compressive force alone upon firing of the projectile through a rifled barrel, the annular groove 2 is cut into the jacket of the projectile in a particular manner such that the 'base wall 4 of the groove forms part of the generated surface of a cone whose apex is directed toward the rearward end or base of the projectile. In accordance with the present invention, the cone whose generated surface includes the base wall 4 of the annular groove 2 has an apex located along a line including the longitudinal axis 15 of the projectile and at a predetermined particular apex angle such that the generated surface is at an acute angle to the longitudinal axis of the projectile. In particular, the conic surface and the base wall 4 of the annular groove 2 extend in the direction of the resultant of deforming forces acting on the driving head band 3. These forces are vectorially represented in FIGURE 3, and include the aforementioned axial force a and radial force 1'. The resultant of these two forces, acting to deform the driving band 3, is represented vectorially as the resultant R. By forming the base wall 4 of the external annular groove 2 as part of the generated surface of a cone having an apex angle the same as the angle of the resultant R, the exertion on the driving band of a tension force included in a couple caused by the radial force 1' is avoided, and the forces acting on the driving band 3 upon firing of the projectile are restricted to compressive force only, directed toward the lower side wall 5.

In order to assure that the driving band 3 is firmly seated in the external annular groove 2 in the jacket of the projectile, the lateral contact surfaces or

sidewalls

5 and 6 of the annular groove preferably are formed as undercuts, as has generally been done heretofore. In accordance with the present invention, however, the inclination of the base wall 4 as part of the generated surface of a cone as described above, permits forming the lower sidewall 5 as an enlarged supporting area for the driving band 3, so as to spread the compressive force applied to the driving band 3 by the resultant R, over as large an area as practical. The radial width of the lower sidewall 5 preferably is from two-fifths to one-half the radial height of the driving band 3.

In order to permit installation of the driving band 3 as close as possible to the ballistic center of the projectile,

while avoiding weakening of the projectile jacket walls, the external annular groove 2 is positioned relative to the thin wall portion 1 of the projectile jacket in a predetermined manner, facilitated by in inclination of the base wall 4. More particularly, the external annular groove 2 is positioned with the forwardmost portion of the groove spaced at a distance from the internal cavity 12 within the thin wall portion 1 substantially the same as the thickness of the thin wall portion of the jacket. The relationship is more graphically illustrated by the dimensions identified as the thickness w of the thin wall portion and the wall thickness g at the thinnest point between the cavity 12 and the external annular groove 2 (FIGURE 1). Where these dimension are substantially equal, in accordance with the present invention, a substantially uniform strength for the projectile jacket is obtained. Further, the inclination of the base wall 4 permits obtaining this substantial equality of the dimensions g and w while the displacement of the forwardmost portion of the external annular groove 2 rearwardly of the cavity 12 within the thin wall portion (identified by the reference character h in FIGURE 1) is less than two-thirds the thickness w of the thin wall portion of the jacket. Thus, a relatively far forward placement of the driving band 3 is obtained, with a coordinate reduction in precession of the projectile as compared with placement of the driving band at the extreme rear end of the jacket.

In order to assure that rotational forces are trans mitted from the driving band 3 to the projectile, the base wall 4 of the external annular groove 2 is provided with a circumferentially spaced apart series of depressions and projections 7, directed in the longitudinal direction only of the projectile. The fact that the projections and depressions 7 extend in the longitudinally direction only of the projectile permits compression of the sintered metal of the driving band 3 under the force of the resultant R as described above, without giving rise to tension forces on the sintered metal body.

In producing a projectile in accordance with the present invention, the driving band 3 to be pressed into the annular groove 2 is formed with a generally trapezoidal cross-sectional configuration, with the base surface 8 of the driving band also forming a portion of a generated surface of a cone. The width b of the driving band, which decreases toward the outer diameter of the ring, is dimensioned to be somewhat smaller than the clear width B of the annular groove 2., and the inner diameter d at the rear edge 9 of the drive band is somewhat smaller than the major diameter D of the projectile jacket. As a result, the driving band 3 must be forced over the rearward end of the projectile until the rear edge 9 of the driving band snaps into the annular groove 2. This operation is faciltated by the tapered base surface 8 of the driving band.

The present invention has been directed particularly to a projectile having a caliber of 20 mm. (0.7874 inch) and the proportion of such projectile are reflected in FIGURE 4. In such a projectile, the acute angle included between the base wall 4 of the annullar groove 2 and the longitudinal axis 15 of the projectile is preferably about 10. The ratio of the clear width B of the annular groove to its depth f is about 1:05, with the clear width B or the annular groove being about 5 mm. (0.19685 inch) and the depth 1 of the annular groove being approximately 2.2 mm. (0.0866 inch). The guide ring 3 is beveled on its outer sides at 16 and 17, with the inclination of these

annular surfaces

16 and 17 toward the longitudinal axis of the projectile preferably being about 25.

I claim:

1. A projectile wherein a sintered metal driving band is protected against fracture and crumbling upon firing of the projectile through a rifled barrel at relatively high velocity and comprising a projectile jacket having a thin wall portion and a thick wall portion rearwardly of the thin wallportion, a pair of longitudinally spaced apart generally radially directed upper and lower sidewalls and an inverted conical base wall defining together with the sidewalls an external annular groove about the projectile jacket in the thick wall portion thereof, the base wall being formed to converge toward the rearward end of the projectile at a predetermined acute angle to the longintudinal axis of the projectile coresponding to the direction of the resultant of the axial and radial forces acting on the driving band upon firing of the projectile and the side and base walls being oriented relative to the thin wall portion of the jacket in such a manner that the smallest dimension of thickness of the jacket measured from the annular groove is no less than the 15 thickness of the jacket at the thin wall portion and the forwardmost portion of the annular groove is spaced rearwardly of the thin wall portion at a distance less than two-thirds of the thickness of the jacket at the thin wall portion, a circumferentially spaced apart series of projections and depressions extending longitudinally of the jacket, on the base wall of the annular groove and a sintered metal driving band in the annular groove and adapted to engage the rifling of a barrel upon firing of the projectile therethrough and to transmit spinning driving forces to the projectile, the annular groove walls and projections and depressions cooperating to substantially restrict the force applied to the driving band upon firing of the projectile to compressive force alone and thereby protecting the driving hand against fracture and crumbling.

References Cited UNITED STATES PATENTS 681,448 8/ 1901 Gathmann 102-93 725,385 4/ 1903 Wheeler 102-93 815,992 3/1906 Wheeler 102-93 1,475,578 11/ 1923 Hatfield et a1. 102-93 2,411,073 11/ 1946 Whitney 102-93 2,856,856 10/ 1958 Michael 102-93 FOREIGN PATENTS 748,006 12/ 1932 France.

SAMUEL FEINBERG, Primary Examiner JAMES FOX, Assistant Examiner U.S. Cl. X.R. 102-52