“Then when the gun is assembled, all the work is done?” queried Hamilton, who was becoming a little tired from his long tramp through the works and among the furnace-heated shops.

“No,” said the other.  “That wouldn’t do at all.  A gun has not only got to shoot, but it has got to shoot straight.”

“But how in the world,” said Hamilton, “can you tell whether a gun will shoot straight or not?”

“One of the most important ways,” said his informant, “is to let an expert look through the barrel.  One of our best men, for example, has done nothing else all his life; his father before him was a barrel-sighter and his son has just entered the works.  He does it this way—­here, you try,” and he handed a barrel to Hamilton.  “Rest the barrel in this crotch,” he continued, “and look at the window.  You see there is a piece of ground glass with a thin black line running across it.  Point the barrel so that it is aimed just below that line, and if you get it right, you will see a reflection of that line running lengthways up the barrel.”

[Illustration:  Making gun-sights true.  Marksmen firing new-made rifles and adjusting the sights until every weapon carries perfectly. (Courtesy of Winchester Repeating Arms Co.)]

Hamilton put the barrel up and looked and looked, but for a minute or two he could not get the direction, then he caught the line.  But the reflection in the barrel was confusing, and it seemed to him that he saw several lines.

“It’s awfully hard just to get that straight,” the boy said, “and it’s dazzling, too.”

“That man you saw there,” answered his guide, as they moved away, “can tell almost to the width of a thread of a spider’s web if a barrel is straight.  Here, too, is another barrel test going on.  You see this man is pushing a soft lead slug which fits the barrel snugly through the barrel by means of a brass rod.  It takes a certain amount of pressure to push the lead slug through the barrel.  Such slight variations in diameter of the bore as one-tenth of a thousandth can be readily detected, for if the barrel is smaller at any point than where it entered, the slug will stick, and if it is the least bit larger at any point, the slug will slide through too easily.  Men accustomed to this class of work can readily detect an increase or decrease in diameter of one ten-thousandth part of an inch.”

“You certainly have it down fine, Mr. Nebett,” Hamilton commented.

“We try to,” responded his guide.  “Then when the barrel experts have had their turn, the gun is assembled and goes to the action men.”

“Who are they?” asked the boy.

“They test the trigger pull, the cartridge ejection, the fall of the hammer, the filling of the magazine, and all such points.  They have two sets of dummies, such as were used for testing the parts.  One must fit, the other not, and so any fault in the mechanism is detected.  The same with ejection,—­we must be sure that a cartridge will not stick.  Then after that—­”