Lieutenant Ogilby smiled. “You’ll pardon me, Mr. Sampson,” he said, “but I happen to know firearms. It’s a hobby of mine. While you are correct in your statement that these firearms are absolutely identical when they’re manufactured, just as automobiles are identical when they leave the factory, before guns have been in use very long, they take on certain individualities. For instance, on this gun, the front sight was a little high. Miss Trent shot low with it. I tried to get her to take a coarse sight, but she couldn’t understand doing that, so I filed the sight down myself. The file marks are quite visible on this sight. Moreover, in order to absolutely check so there could be no question of doubt, I went out to the place where we had done our target shooting, at the request of Mr. Mason, and picked up the empty shells which had been ejected from the gun when I reloaded it.”
“What have the empty shells got to do with it?” Sampson asked sneeringly.
“Simply this,” Lieutenant Ogilby said. “Before the science of ballistics learned that bullets fired from a gun could be identified by marks made by the rifling, the only method of determining whether a shell had been fired from a given gun was to center the firing pin on the percussion cap. Firing pins, theoretically, strike in the center of the percussion cap. Actually, they do no such thing. Furthermore, in the course of use, each firing pin develops little peculiarities of its own. There is not only the position of the indentation made by the firing pin on the percussion cap, but there are also little irregularities in that impression which are distinctive. I satisfied myself that each one of those shells had been fired from this same gun.”
“You didn’t have the gun to compare those shells with,” Sampson said.
“No, but I had a photograph of the cylinder of this gun which was furnished me by a newspaper, and which I have every reason to believe was authentic. But just a minute, Mr. Sampson, if you wish, I’ll make that check right here and now.”
He produced a discharged shell from his pocket, took the gun from Hogan, opened it and said to Hogan, “You’re an expert. You can see for yourself.”
Hogan leaned forward, and Sampson said, “I object to that form of examination. Let the witness answer the question so the jury can get it.”
Mason grinned and said, “He’s your own expert. Take him away if you don’t want him there.”
Hogan stepped back, looked at Sampson, and nodded almost imperceptibly.
“Just step up to the jury,” Mason said to Lieutenant Ogilby, “and show them the marks made by the firing pin on the discharged shell which is in the cylinder of the weapon, and the discharged shell which you hold in your hand and which you picked up where you had been engaging in target practice.”