Anybody?
The picture you are referencing is not the groove. It is the land. The land measures 1.8 mm just like Frazier stated a carcano barrel's lands and grooves are supposed to be. The barrel's groove is 3.3 mm
Frazier referring to a carcano's lands and grooves while discussing the Walker Bullet. The same as the barrel cast from CE 139
Mr. EISENBERG - Can you describe the general rifling characteristics which you referred to?
Mr. FRAZIER - Yes. They consist of impressions from four lands and grooves. The bullet is mutilated on a portion of its surface. However, it can be determined that there were four land impressions and four groove impressions originally on this bullet.
The width of the land impression is 7/100ths of an inch, that is 0.07 inch--whereas the width of the groove impression is 0.13 inch, or 13/100ths of an inch.
The bullet is flattened so that it was not possible to measure its diameter. However, by adding the land width to the groove width, and multiplying by the number of lands and grooves, you can determine the circumference of the bullet and mathematically determine its diameter, which in this case corresponds to 6.5 mm. ammunition, or approximately .267 inch.
Mr. EISENBERG - What was the direction of the twist?
Mr. FRAZIER - To the right.