74 )¥. B. Morton on 



U) Five spiral grooves are cut on the surface of the barrel 

 separated by "lands" of the same width as the grooves. In front 

 of the chamber the grooves attain their full depth of -006 in. 

 gradually, so that the beginnings of the lands are like sloping 

 chisels against which the bullet is driven. Five sloping grooves 

 are thus cut in the copper-nickel skin of the bullet. It then 

 travels along the barrel, turning as it goes, like a very short screw 

 turning in a very long nut. One complete turn is made in 10 in. 

 of travel, or 21 turns along the length of the barrel. The velocity 

 of the bullet as it leaves the rifle is given as 2,440 feet per second, 

 so it is spinning at almost 3,000 revolutions per second. 



(2) During its flight the bullet is subject to gravity and air 

 resistance. The latter acts in the line of the bullet's motion and 

 its effect is the same as if the bullet were placed, at rest, in a 

 wind blowing past it with the same speed, viz., at the beginning, 

 a wind of about 1,600 miles an hour. Owing to the high velocity 

 the path of a rifle bullet, at moderate ranges, is very nearly 

 horizontal. Even for a range of 1,000 yards the elevation of the 

 rifle is only about 1°. It follows from this that the wind-force 

 on the bullet is nearly horizontal and so the rise and fall, under 

 gravity, go on almost independently of the air-resistance : e.g., a 

 bullet fired horizontally will fall about as much in a given time 

 as if it had been simply dropped from rest. 



The effect of air-resistance is most striking in decreasing the 

 attainable range. The maximum range is only about one-tenth 

 of what it would be in the absence of air, say 2j miles instead 

 of 25 miles. The bullet leaves the muzzle with a speed of about 

 800 yards per second. But the distance covered in the first 

 second of its motion is only 600 yards and in the second second 

 400 yards. As the speed of a projectile increases so does the 

 air resistance, but no law of a simple kind holds for the relation 

 between the two. Experiments show that there is a specially 

 rapid increase in the resistance in the neighbourhood of 1,100 

 feet per second. This is the velocity of sound through air. 

 Instantaneous photographs of a flying bullet taken by electric 



