PENETRATION OF IRON I'LATES BV STEEL SlIoT, 



400 



with a 6-22-ineh shot. This was determined in the following manner by a 

 preliminary experiment. 



The weight of the steel shot was 63-87 lbs., its diameter 6'22 inches, and 

 the required velocity 1116-6 feet. It was found by experiment that a shot 

 of this description would be moving with a velocity of nearly lllG-6 feet at 

 100 yards distance, if it were fired with a charge of G lbs. 11 ozs. of powder. 

 This charge was therefore employed in round 1047 with the following results. 



Shot struck 4-5-inch imbacked plate about the centre and just penetrated 

 the plate, the .shot rebounding (i j-ards. From this result it appeared that a 

 " work" of about 552 foot-tons was just capable of piercing a 4-5-inch un- 

 backed plate, and that, practically speaking, the assumption that the resist- 

 ance varies as the scjuare of the thickness was correct. 



The experiments might therefore proceed. 



It appears from the above Table that when the weight of the projectile 

 varies from 35 to 106 lbs. the velocity wUl vary from 1496 to 864 feet, if the 

 " Avork " is required to be constant. 



In order therefore to strike the 4-5-inch plates with a constant '' work" 

 of 552 foot-tons, we must so proportion the charges of powder that the seve- 

 ral projectiles on impact may be moving with tbeir corresponding velocities 

 as shown by Table IV. This has been done by observing the velocity at 

 100 yards of a series of cast-iron projectiles of as nearly as j^ossible the same 

 weight as the steel shot, the cast-iron projectiles corresponding to the 

 spheriml steel shot being a shell brought to the proper weight by being filled 

 ■\vith lead. 



The following Table shows these charges determined by experiment : — 



Table V. — Showing the approximate charges with which various steel hemi- 

 spherical-headed shot should be fired from the 64-pounder M L gun, in 

 order that the work may be constant at 100 yards. 



The charges given in the last Table are termed " apjivoximate,'^ because it 

 would be imtrue to assert that these charges would give the absolute veloci- 

 ties required, although they are the nearest approximation we can make, or 

 the probability of the velocity being the required one is nearer with these 

 charges than with any others. 



The charges having thus been determined, the diftercut projectiles were 

 fired at the 4-5-inch unbacked plates ; the velocity of each projectile was 

 observed at a short distance in front of the plate, and the small loss of velo- 

 city due to the resistance of the air during this short distance was calculated 

 by the most approved theory, which, although it may not give results which 

 are strk-thj correct, is practically sufficiently near the truth when the range is 

 small. 



The following Table gives the velocities, both observed at 80 feet distance 

 from the plates, and calculated on impact. The penetration of each shot is 

 given in the column of remarks. 



