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Ballistic testing can determine whether or not an empty shell casing was fired from a specific weapon to the exclusion of every other weapon in the entire world. Before shooting, the shell casing is placed against the breech face and the firing pin. When the pin strikes the primer, the bullet is fired off and the shell casing is thrust against the breech face of the weapon. This causes a permanent mark on the base of the empty shell, i.e. the distinctive fine lines etched onto the breech face put their "fingerprint" on the base of the empty shell.
Joseph Nicol (Superintendent of the Bureau of Criminal Identification and Investigation for the State of Illinois) along with Cortlandt Cunningham, Robert Frazier and Charles Killion (of the Firearms Identification Unit of the FBI Laboratory in Washington D.C.) each examined the shells found at the Tippit scene and Oswald's revolver, which he ordered from Seaport Traders, Inc. Each of these experts determined that the shells were linked (through ballistics) to Oswald's revolver, to the exclusion of every other weapon in the world.
Mr. EISENBERG. Now, were you able to determine whether those bullets have been fired in this weapon?
Mr. CUNNINGHAM. No; I was not. Mr. EISENBERG. Can you explain why? Mr. CUNNINGHAM. Yes, sir.
First of all, Commission Exhibit No. 602 was too mutilated. There were not sufficient microscopic marks remaining on the
surface of this bullet, due to the mutilation, to determine whether or not it had been fired from this weapon
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Mr. EISENBERG. Now, you said that there were three bullets of Winchester-Western manufacture, those are 602, 603,
and 605, and one bullet of R.-P. manufacture.
Mr. CUNNINGHAM. That is correct.
Mr. EISENBERG. However, as to the cartridge cases, Exhibit 594, you told us there were two R.-P. cartridge cases
and two Western cartridge cases.
Mr. CUNNINGHAM. That is correct.
Mr. EISENBERG. So that the recovered cartridge cases, there is one more recovered R.-P. cartridge case than there
was recovered bullet?
Mr. CUNNINGHAM. Yes.
Mr. EISENBERG. And as to the bullets, there is one more recovered Winchester-Western bullet than there is
Winchester-Western cartridges?
Mr. CUNNINGHAM. That is correct
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