GRINDING AND TURNING. 445 



the whole extent of the barrel, a stream of water playing upon the 

 metal during the whole process, for the purpose of keeping down 

 the heat that is engendered by the severe friction of the bit, and 

 which, if alloAved to increase to its full extent, might injure the 

 quality of the metal. 



The first or rough boring being finished, a bit of still larger size 

 is now introduced, and the same process gone through with until 

 the barrel is entirely freed from all unevenness and its whole inter- 

 nal surface made to shine like a mirror. 



If the barrels, after repeated borings, should still exhibit an un- 

 even surface and present flaws and depressions, they are rejected, 

 and the metal returned to the forge, as it would be unsafe to bore 

 them still thinner when the metal is so soft and frangible. 



Some gunsmiths bore barrels by hand ; and a good workman will 

 make a beautiful instrument in this way, although it will take 

 treble the time to finish it. The utmost nicety is requisite in the 

 boring of barrels, as they should be perfect cylinders, and of exact 

 calibre throughout their entire length. When they have passed 

 the inspection of the lynx-eyed workman to whom this important 

 process is confided, the barrels are handed over to the grinder, to 

 be ground, turned, and polished. 



GRINDING. 



The barrels being bored, the grinder submits them to the friction 

 of a revolving stone, for the purpose of freeing them from all the 

 scales and roughness which cover them when they come from the 

 hands of the welder. 



TURNING. 



A smooth surface being obtained by the application of the stone 

 by the grinder, the barrels are next to be turned, which is ac- 

 complished either with a common turning-lathe or a self-acting 

 machine. 



A mandrel exactly fitting the size of the barrel is first intro- 

 duced ; the barrel is then placed in the lathe and the machine set 



