Q. Can you explain how you are able to come to a conclusion that a cartridge case was fired in a particular weapon to the exclusion of all other weapons ?

Mr. FRAZIER. Yes, sir; during the manufacture of a weapon, there are certain things done to the mechanism of it, which are by machine or by filing, by grinding, which form the parts of the weapon into their final shape. These machining and grinding and filing operations will mark the metal with very fine scratches or turning marks and grinding marks in such a way that there will be developed on the surface of the metal a characteristic pattern. This pattern, because it is made by these accidental machine-type operations, will be characteristic of that particular weapon, and will not be reproduced on separate weapons. It may be a combination of marks that--the face of the bolt. may be milled, then it may be in part filed to smooth off the corners, and then, as a final operation, it may be polished, or otherwise adjusted during the hand fitting operation, so that it does have its particular pattern of microscopic marks.

The bolt face of the 139 rifle I have photographed and enlarged in this photograph [Commission Exhibit No. 558] to show the types of marks I was referring to.

The marks produced during manufacture are the marks seen on the bolt face; filing marks, machining marks of the various types, even forging marks or casting marks if the bolt happens to be forged or east. And then variations which occur in these marks during the life of the weapon are very important in identification, because many of the machining marks can be flattened out, can be changed, by merely a grain of sand between the face of the cartridge ease and the bolt at the time a shot is fired, which will itself scratch and dent the bolt face. So the bolt face will pick up a characteristic pattern of marks which are peculiar to it.