The caliber is normally determined by the bore diameter.
Mr. Eisenberg. Can you explain how you made the identification of this rifle?
Mr. Frazier. I identified it pictorially by comparing it with pictures in reference books. And the actual identification was of the manufacturer's name appearing on the barrel and serial number, which indicated it was an Italian military rifle.
Mr. Eisenberg. Did you independently determine the caliber of the rifle?
Mr. Frazier. Yes, I did.
Mr. Eisenberg. Can you tell us how you did that?
Mr. Frazier. The caliber and the caliber type may be confusing here.
The caliber, being the diameter of the barrel, is determined in two ways—one, by comparing the barrel with 6.5mm. Mannlicher-Carcano ammunition, which we also chambered in the weapon and determined that it actually fit the weapon. And, secondly, we measured the width of the barrel with, a micrometer. And in that connection, I would like to point out that we made a sulphur cast of the muzzle of the weapon which permitted us to use a micrometer to determine the land width and the groove width in the barrel.
Mr. Eisenberg. Do you have that sulphur cast?
Mr. Frazier. Yes, I do.