440 MR. P. HOPKINSON ON MEASURING THE PRESSURE PRODUCED IN THE 



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Pressure Produced by tlie Impact of Lead Bullets. 



The pressure which should be produced by the impact of a lead bullet can be 

 predicted theoretically, and the study of this pressure was made rather with a view 

 to checking the method than in the hope of discovering any new facts. At velocities 



exceeding 1000 feet per second lead behaves on impact 

 Pjg.4. against a hard surface practically as a perfect fluid. 



The course of the impact is shown in fig. 4. The base of 

 the bullet at the moment of striking is at A ; a little later 

 it is at B. Assuming perfect fluidity the base of the 

 bullet knows nothing of the impact at the nose and 

 continues to move forward with unimpaired velocity. 

 Hence the time elapsing between the two positions shown 



in the figure is -^. The momentum which has been destroyed up to this time is to 



a first approximation that of the portion of 

 the bullet which has been flattened out, 

 namely that portion shown shaded in the 

 dotted figure. Knowing the distribution 

 of mass along the length this is easily ^ 

 calculated. This simple theory is subject ^ 

 to some qualifications due partly to want ^ 

 of perfect fluidity, and partly to the fact ^j- 

 that the sections of the bullet are not s 

 brought right up to the face and there 

 stopped dead, as is assumed in the theory, 

 but are more or less gradually retarded or 

 deflected in the region of curved steam-lines 

 at C. These corrections are, however, most 

 conveniently introduced when comparing 

 the theory with the experimental results. 



The bullets used were of two patterns, 

 one the ordinary service form (Mark VI.) 

 and the other a soft-nosed bullet supplied 

 on the market for sporting purposes. Both 

 are of lead, encased in nickel. Sections of 

 the bullets are shown in fig. 5.* Sample 

 bullets were sawn into sections, and the 

 sections weighed. The distribution of weight along the length thus determined 



The soft-nosed bullet (lower figure) has four longitudinal saw-cuts in the nickel casing ; the section is 

 taken through two of these cuts. 



5 -75 I-O 



Lengths, Inches. 





