140 BARREL AXIS. 



but also always keeps its point forward. By the 

 bullet being thus expanded, and so much en- 

 larged as to fit the barrel and grooves tightly, 

 none of the explosive power of the gas engen- 

 dered by the ignition of the charge is allowed to 

 escape, but the whole propelling force acts 

 upon the projectile. There is also a much 

 better chance of the whole of the powder being 

 burnt. 



The barrel is a tube of iron, of 

 The Barrel. 



which the sides of the interior, or 



bore, are parallel, but those of the exterior con- 

 verge, it being necessary that the metal of the 

 breech-end should be very much thicker than at 

 the muzzle, towards which it gradually tapers, 

 as it has to stand the force of the explosion of 

 the charge. In consequence of this contraction, 

 every barrel has in itself a certain degree of 

 elevation but of this more anon. 



The axis of the barrel is an imagi- 

 The Axis. 



nary line drawn through the centre of 



the bore, and parallel to the interior sides. 



