"We might make an alloy of copper and zinc."
"Oh! You mean brass?"
"Yes; that is readily cast and easily worked."
"But what shape shall we make the bullets?"
"They should be made long, with a pointed forward end."
"Why is a long bullet better than a round or globe-shaped ball?"
"There are several very important reasons. First, momentum is a prime element in a missile. A long one contains double the metal of a spherical one. Second, it can be made so that it will expand when the explosion of the powder takes place."
"In what way does it expand?"
"You have noticed that the rear end of the bullet has a cavity. When the explosion takes place the thin shell at the rear end of the bullet expands, so that it tightly hugs the bore of the gun."
"What is the object of having it do that?"