the shell ; but in all recent types the cap is made to conform to the contour of the head of the shell. The use of the ogival radius determines the breadth across the front of the cap, while a certain thickness through the point is required to give satisfactory armour- piercing qualities, and the combined effect of these two dimensions prevents any appreciable reduction in the weight of the cap. The use of a cap introduces a serious disadvantage in that extra weight is put into the head, wheteas the heavier part of a shell should be the base. The cap is attached to the head of the shell by notches in the shell or by interrupted ribs. The sheath of the cap may require to be built up from two or more pieces; and with heavy shell the cap may be in four pieces. (F. M. R.)
Fig. 10, showing typical outlines of German shell, taken from the German Heavy-Artillery Ammunition^ Handbook of 1917, may be of interest as illustrating the tendencies of design discussed above. Here (a) shows the old-fashioned 2 c.r.h. shell, with a front steady-
German 15 cm Howitzer H.E.Shell. 1914 Length about 3 calibres 2 c.r.h.
Contoured Nose Fuse, Forward steadying band &2 Driving bands.
German 15 cm Howitzer Shrapnell 1916 Internal T & P Fuze. False Cap. 10 c.r.h. 6 calibres long 2 Driving bands & decoppering ring.
German 17 cm H.E.Shell. 4 7 calibres long .streamlined with False Cap, Nose Fuze,
2 Driving bands & decoppering ring, about 11 c.r.h.
FIG. 10.
ing band of copper; (b) shows a false-cap shell without stream-lined base; (c) shows a stream-lined shell proper. (C. F. A.)
PROJECTILE FORM
The general form of the elongated projectile in use for many years prior to the World War is illustrated in fig. i. The body
FIG. i.
(1) is cylindrical in form and of uniform diameter except that the " bourrelet " or shoulder swell (3), intended to form a bearing on the lands of the gun, is slightly larger in diameter. 1 Special care is taken in accurately machining this bourrelet, and the aver- age amount by which the diameter of the bourrelet is less than that of the gun is i/iooo of the calibre.
It was the usual practice for many years to make the head
(2) of ogival shape, with the centre of the circular arc in or near the plane of the front end of the body and with a radius of arc varying from i : /2 to 2 l / 2 calibres. When a point fuze was used, as illustrated in fig. i, its projecting end was sometimes, but not by any means always, made to conform to the shape of the head.
The rotating band (4) was placed at a distance of from Vis to i calibre from the base, and its width was from '/ to V calibre. In addition to engaging the rifling in the gun and so causing the rotation of the projectile, other functions of the rotating band are to provide a rear bearing for the projectile, to provide a definite
1 In many shells this bourrelet does not appear, the walls remain- ing uniform from the driving band to the beginning of the head. In these cases a slight outward splay is given to the upper part.
(C. F. A.)
seating for the projectile in loading, and to prevent the undue escape of powder gas around the projectile when the gun is fired.
In fig. i, which illustrates a field projectile, the shell cavity is either cylindrical or larger in diameter toward the front end of the body, and the fuze is at the point.
In naval or coast-defence projectiles, where penetration of armour is desired, the general form is as illustrated in fig. 2.
FIG. 2.
The great shock to which the projectile is subjected on impact with armour requires thickening of the walls at the forward end and shortening of the cavity. For the same reason the fuze can no longer be placed in the point but must be placed in the base. It is found that armour-piercing properties are improved by adding a soft metal cap (7) to the hard head (2). In order to get a smooth form of head, a hollow " false ogive " (8) was added to the forward end of the cap.
Experiments to Improve Form. Previously to 1900, bullets for small arms had rounded points and " square " bases. Experiments started about that time in Russia indicated that a marked improve- ment could be obtained in flatness of trajectory and this improve- ment opened the way for experiments in all countries to deter- mine forms of artillery projectiles that would give increased ranges (or, for similar ranges, natter angles of descent and higher terminal velocities). At that period (about 1907) the mounting of high- power ordnance, both field and naval, did not usually permit of elevations in excess of 20 degrees. There was a possibility of in- creasing ranges by modifying existing mounts or building new ones, but such a proceeding would have been expensive, and, as will be shown, might not in many cases have increased the range as much as the use of an improved projectile with the old elevation.
Early Improvements in Head. Even before the adoption of sharp- pointed bullets in small arms, Pctrovitch, a Russian, had about 1902 brought out a mathematical discussion of the form of surface which would encounter the least resistance in passing through an elastic medium. This paper helped to encourage experiments to im- prove the form of head. Firings were made in the United States in 1907 from a 6-in. gun with a io6-lb. projectile having a tangent ogive of 7 calibres radius, using a muzzle velocity of approximately 3,050 ft. per second. The outline of this projectile is shown in fig. 3.
FIG.
The range obtained was 12,800 yd. at an angle of elevation of 7, as against 7,800 yd. obtained with the same weight of projectile with a 2-calibre radius and fitted with an armour-piercing cap as shown in fig. 2, without the false ogive. The muzzle velocity with the latter projectile was 2,990 ft. per second. This increase in range of 60 % led to other experiments. As it was desired , however, to retain the armour-penetrating efficiency of these projectiles, attention was principally given to the design of a form of head and cap which would make the projectile efficient both for armour pene- tration and for range.
Firings were made with the same projectile having the point rounded off, as shown in the following table, which gives the cor- responding range and coefficient of form :
Radius of Point In.
Range Yd.
Coefficient of Form
o-75 1-25
1-75
12,920 1 1,940 10,730
505 600 762
It was supposed by some, at that time, that the air resistance was principally dependent upon the form of junction of head and body; that little additional resistance would arise if the sharp point was rounded off: and that the rounded form of point would add to the efficiency of the projectile in armour-piercing. The firings indicated a marked effect on range of even a slight rounding of the point. Armour-piercing projectiles of the form shown in fig. 3 did not seem
