"To give the ball the benefit of the charge of powder exploded. If it does not fit tightly in the bore, more or less of the powder will pass the ball, and thus the ball loses part of its force."
"What is the object of rifling the gun?"
"The object is to impart to the bullet a spiral motion, as it moves through the air. Metals have not the same density on all sides and this is particularly true of molded balls. As a result, when projected from the gun, the heaviest side has a tendency to divert the ball and make it more or less erratic in its motion, and, therefore, inaccurate. The spiral motion has the effect of minimizing this difficulty. The cavity formed at the rear of the projectile was devised particularly to cause the thin lip of the bullet to be driven into the grooves formed in the gun barrel, and by that means the boring motion was transmitted to the bullet."
"But as we have no means of rifling our guns, there will be no necessity of putting the cavity in the rear end of our bullets."
"We must have the cavity there, by all means."
"What for?"
"Simply because we do not want the bullet to turn around and travel end over end after it leaves the gun."
"How does the cavity prevent this?"
"You have probably forgotten that a body travels through the air with its heaviest end foremost. When a cavity is made it is lighter at that end. Without the cavity, if the forward end is pointed, it will, on leaving the gun, turn around and go through the air with the blunt end foremost."
The molds were made, as directed, of a hard brass composition, and when they were ready to cast them the Professor cautioned against making any castings with the molds in any position except upright, so that any inequality in the density of the metal would not form itself on the side of the cast article.