The rifling refers to the grooves in the barrel that impart spin to the bullet. The rifling in most .30 caliber barrels is one turn in, between 10 & 12 inches. This will stabilize most .30 caliber bullets, 130 to 200 grains. It would be difficult to determine by eye. Most companies reference the rifling spin in the spec.'s of their rifles. You can determine the rate of twist by putting a tight fitting cleaning rod into the muzzle and mark a line along the cleaning rod. Push the cleaning rod through until you see the line again. The distance you pushed the rod through is your rate of twist. There is actually a formula that is used to determine the ideal rate of twist.