PENETRATION OF IRON PLATES BY STEEL SHOT. 



417 



shot, -we shall find that in almost every instance where the projectiles were 

 monng at a velocity not exccediug 1200 feet, the cast-iron shot may be 

 said to require about 2| times the " work " necessary to effect the same 

 amount of perforation with steel shot. When, however, the velocity of the 

 cast-iron shot is very high, this proportion is reduced to about 1-7. This 

 latter result is due to the influence which the element velocity has in the 

 penetration of cast-iron shot. If we suppose two cast-iron projectiles to be 

 of the same form of head and diameter, and to be animated with the same 

 amount of energy or "work," consisting in one case of a heavy shot and 

 low velocity, and in the other of a hght shot and high velocity, the oifect 

 of these projectiles wiU be very different. 



The damage in the case of the low velocity will be spread over a larger 

 siirface, and the absolute indent will be small ; while in the case of the high 

 velocity the effect will be confined to the immediate neighbourhood of the 

 point of impact, and the result will be a deep indent. This result with cast- 

 iron shot is so well known that it seems almost needless to allude to it ; we 

 may, however, select one or two examples for record. 



Thus the 'BeUerophon' target was struck by two projectiles fired from 

 the 10-5-inch gun (rounds 717-719). The first consisted of a spherical 

 shot of 150 lbs., moving with a velocity of 15-47 feet, and a consequent 

 " work " of 76 foot-tons per inch of shot's circumference ; the second, of an 

 elongated shot of 308 lbs., moving with a velocity of 1090 feet, and consequent 

 " work " of 77 foot-tons per inch of shot's circumference. 



In the first instance the indent was 5 inches, and the damage was con- 

 fined to the point struck. In the second instance the indent was 1-G inch, 

 but the plate was cracked and bulged over a large area. 



The foUo-wing Table shows the absolute thickness of plate which can be 

 penetrated by cast-iron shot fired from various guns with service-charges : 

 the guns were at a distance of 100 yards from the plates, with the excep- 

 tion of the 68-pounder, which was at 200 yards (see Appendix, Table X.) : — 



Table VII. — Showing the difterence between the effects produced by cast- 

 iron and steel shot, when fired at iron plates. 



If we compare the results given by this Table with the effect of steel pro- 

 jectiles, it wiU appear that the cast-iron shot requires about 2| times the 

 „work" of the steel shot to effect the same penetration, except' where the 

 velocity of the cast-iron shot is large. This Table has been di-awn up with 

 a view of showing the difference in effect of cast iron in comparison with 

 steel shot. 



* From actual experiment on plates of various thicknesses. 



t Deduced from experiments with various gims at plates of 5-5, 4-5, 3-5, 3-0, .and 25 

 inches thickness. t Shot moving at a high velocity, 



1866. 2e 



