Q. And what did you find on that examination ?

A. There would be no similarity in the individual microscopic characteristics between the two bolt faces.

Q. There actually was none ?

A. No there was none.3

Q. How are you able to conclude that a given bullet was fired in a given weapon to the exclusion of all other weapons, Mr. Frazier?

A. That is based again upon the microscopic marks left on the fired bullets and those marks in turn are based upon the barrel from which the bullets are fired.

The marks in the barrel originate during manufacture. They originate through use of the gun, through accidental marks resulting from cleaning, excessive cleaning, of the weapon, or faulty cleaning.

They result from corrosion in the barrel due to the hot gases and possibly corrosive primer mixtures in the cartridges used, and primarily again they result from wear, that is, an eroding of the barrel through friction due to the firing of cartridges, bullets through it.

In this particular barrel the manufacturer's marks are caused by the drill which drills out the barrel, leaving certain marks from the drilling tool. Then portions of these marks are erased by a rifling tool which cuts the four spiral grooves in the barrel and, in turn, leaves marks themselves, and in connection with those marks of course, the drilling marks, being circular in shape, there is a tearing away of the surface of the metal, so that a microscopically rough surface is left.

Then removing part of those marks with a separate tool causes that barrel to assume an individual characteristic, a character all of its own.

In other words, at that time you could identify a bullet fired from that barrel as having been fired from the barrel to the exclusion of all other barrels, because there is no system whatever to the drilling of the barrel. The only system is in the rifling or in the cutting of the grooves, and in this case of rifle barrels, even the cutters wear down as the barrels are made eventually of course having to be discarded or resharpened.

Q. Have you examined consecutively manufactured barrels to determine whether their microscopic characteristics are identical?

A. Yes, sir; I have three different sets of, you might say, paired barrels, which have been manufactured on the same machine, one after the other, under controlled conditions to make them as nearly alike as possible, and in each case fired bullets from those barrels could not be identified with each other; in fact, they looked nothing at all alike as far as individual microscopic characteristics