Originally Posted by
nhrifle
The 6 and 9 refer in some way to the radius of the arc beginning at the straight shank of the bullet (where it seats in the case) following a curved line to the point. In machinist terms, I would call it an arc segment, which basically is a piece of a circle. The smaller the number, the more defined the curve of the ogive radius. Think of it like this -- take a 6s ogive for example. Imagine a 6" circle. Divide that up into pie wedge shaped segments in which we concentrate on the curved "crust" part, each segment the same length as the curved part of the bullet described above. Now do the same with a 9" circle. Since the 6" circle has a sharper radius than the 9" circle, the arc segment from the 6" circle will have more of a pronounced curve than that of the 9".
Long story short, the 6s ogive will have more of a curve toward the point, while a 9s will look more like a sharpened pencil. I really hope this makes sense. Describing a geometrical shape is not one of my strengths.