y8o The Shot-Gttn. 



the barrel directed to the bright sky, when you will observe the open- 

 ing of the muzzle and, surrounding it, three or four bright, broad 

 rings, which will all be concentric with the bright circle of the muzzle 

 if the barrel be straight* _ n 



A study of the accom- 

 panying carefully drawn 

 diagram will show how 

 these circles are produced j 

 by the reflections of the 

 light of the pinhole from 

 the sides of the barrels. 



Gunmakers use a meth- ""•-... \ / 



od of testing called " shad- 

 ing," which is applied by holding the breech a few inches from the 

 eye and looking through the barrel at the top of a window-sash and 

 seeing if its image has straight edges as it appears reflected along 

 the sides of the interior of the barrels. 



The choke of a gun, and the dimensions of any part of the bore, 

 may be examined by long-legged calipers supplied with a spring 

 and an index-gauge ; or, by well oiling the interior of the barrel and 

 then taking a plaster cast of it, on which measures can be made 

 with a pair of vernier calipers. 



Chokk-bored Barrels. — It is not possible to state who was the 

 first inventor of choke-boring. It is probable that one or another 

 of the different modes of boring, which differ from that producing a 

 plain cylinder, has been used from time to time during the past one 

 hundred years ; but it is certain that our countryman, Joseph W. 

 Long, first called public attention to the excellence of the system 

 of choke-boring. From this country the knowledge of its merits 

 went to England, and now choke-boring is practiced by gunsmiths 

 throughout the world. 



* The reader may amuse himself with a few experiments which will make clear to 

 him the philosophy of these methods of testing gun-barrels. Take two or three glass 

 tubes about one-half inch in bore and eighteen inches long. One of these tubes should 

 be as straight as can be selected at the glassware dealers. The other should appear 

 evidently bent or curved. Cover the outside of these tubes with black varnish or 

 cloth, so as to exclude the light. Close one end of each tube with a circle of card-board 

 with a pinhole in its center. On looking through the tubes, you will see the circles 

 concentric with the pinhole in the straight tube and eccentric in the curved ones. 



