Vibrations of Rifle Barrels. 



34H 



at F 1 and with the initial velocity V - % the trajectory of this shot will 

 always be a constant distance PiP 2 below the trajectory through P p 

 and will therefore strike the target T 1 at this distance below the 

 centre. If a second target, T 2 , is placed at a distance P1P2 ( = ft) 

 behind Ti so that P1T1 = P2T2 = R, the second target will be struck 



Fig. 12. 



a/5 below the hit in the first target ; hence since P]P 2 = fta, the error 

 due to the variation of initial velocity is « (a +'/?). /? may be found 

 from the range tables of any rifle by the relation 



P = E . da/dR. 



Applying this to the Lee-Enfield, the following table shows the 

 errors due to a variation of 40 feet per second in the initial velocity, 

 on the assumption that the direction of the shot is not affected by 

 " jump." 



Table VII. 



ft = 54 feet == distance from muzzle at which the speed has fallen 

 40 feet per second. 



Hange in 

 yards. 



a. 



j3. 



a (a + 13). 











feet. 





100 



4' 



48' 



0-141 



l'-6 



500 



31/ 



43' 



1-17 



2'16 



1000 



88' 



144' 



3-8 



4'35 



1500 



177' 



320' 



7-8 



6'-0 



2000 



305' 



570' 



13-8 



r-8 



2500 



477' 



980' 



23'0 



10'- 5 



These errors are comparable with, but, especially at the longer 

 ranges, greater than what the best shots are liable to in practice, so 

 that with this particular rifle the compensating action of the variation 

 of "jump " is a distinct advantage.* 



For some time I was under the impression that the complete elimina- 

 tion of the effect of "jump" which could be effected by a recoiling 

 barrel, such as has been used in some repeating rifles, would lead to 



* The fact that in this rifle variation of "jump" had a corrective effect was 

 noticed by the late Sir Henry Harford. 



