344 



Vibrations of Rifle Barrels. 



improved accuracy in shooting ; but in view of the above results it 

 would appear that this is not the case.* 



The present inquiry shows that in the design of a rifle it is most 

 important to consider the relations between the explosion force and 

 the natural periods of the rifle, considered as an elastic structure, and 

 that probably the compensating effect above mentioned might be made 

 of more use than it is at present. 



For this purpose the explosion curves for various classes of ammuni- 

 tion and the variations to which they are liable should be accurately 

 known, and the proportions and length of the barrel, as well as the 

 attachment of the barrel to the stock, should be so arranged with 

 regard to the nodes of the system as to make variation of "jump'* 

 with the variation of initial velocity most nearly balance, within certain 

 ranges, the alteration in the trajectory which gravity would otherwise 

 effect in virtue of the altered initial velocity. 



To show the sort of advantage which may be obtained by this 

 means, we may, for example, suppose the rifle to be so constructed 

 that for some particular class of ammunition the variation of "jump" 

 due to a ± 40 f.s. of initial velocity causes downward or upward 

 variation of 6' in the initial direction of the shot. Then by subtracting 

 6' from E in Table VII, and multiplying by E, we get the following 

 results : — 



Table VIII. 

 Error due to ± 40 f.s. in initial velocity. 



Error 



Without jump. With jump. 



100 yards ± 0'14 feet. + 0-38 feet. 



500 „ 1-17 „ 1-70 „ 



1000 „ 3-8 „ 1-23 „ 



1500 „ 7-8 „ 0-00 „ 



2000 „ 13-8 „ ±3-15 „ 



2500 „ 23-0 „ 9-8 „ 



Such a correction, if it can be realised without an inconvenient 

 construction of the mechanism, would be valuable for military pur- 

 poses now that long-range fire is becoming of such great importance. 



* There is another form of " jump," however, in the Lee-Enfield rifle, whose 

 absence is most desirable, as it introduces horizontal, movements of the barrel. It 

 depends, not on the acceleration of the shot, but on the statical pressure of the 

 powder gas acting on an unsymmetrical breech-closing action, and the remedy, as 

 well as the disadvantages, are so clear in this case as not to call for further remark. 



