I have heard the terms secant ogive vs. tangent ogive used to describe bullet geometry. I understand what the ogive is, but I don't understand the differences between the two types (my geometry and calc classes were more than a few years ago). Can someone enlighten me?

edited version:

-

Let me try:



1) the figure r mentioned with the secant/tangent expression describes the radius of a circle where the radius is expressed in calibers (bullet diameter):

A small figure r yields a small circle, i.e. a more rounded ogive than a larger circle (bigger figure).

Sierra bullets, for example, have a lower figure than low drag bullets. A larger figure is beneficial for the BC, but detrimental to the bearing surface and the length (stability in flight -> twist).



2) you draw a circle and two lines. One line is just touching the circle line, the other goes through the circle line thus cutting off a part of it.

The first line is a tangent, the second a secant.



3) A bullet has a parallel part (bearing surface) onto a point where the ogive starts. Rectangular to this point will be the center point of the circle (r calibers away) for the tangent type, while the radius rectangular to the secant type is always on the cylindrical body of the bullet (i.e.: the angle between parallel body and the radius at the junction point is always less 90 degrees for the secant) , and here (on the junction of the two lines) the line of the bearing surface and the ogive circle line meet - either touching (tangent), or cutting (secant).

Holding a bullet in the right angle to the light will show you a rim which indicates a secant type bullet.

Thanks, you answered my question perfectly. Of course I did have to break out paper and a straightedge to figure out what you were explaining to me (my fault, not yours).
So it's really about finding a balance, or moving the balance between a higher BC on one hand, and a longer bearing surface, balance and stability on the other. Bullet diameter and weight dependent, of course. Or something like that. I'd better shut up now.

Funny thing is, if you exaggerate the secant ogive by reducing the r value (diameter) the projectile starts to look like the old-style tank and artillery projectiles.

"Thanks, you answered my question perfectly"



Unfortunately not, sputster. I edited my post as I left something out about the secant angle to the bullet shaft. Please read my post again.



It is true, secant types are always a bit plumper with the same r as tangent ogive types. (The Krupp reference bullet on which the Mayewski/Ingalls tables are based is a secant type bullet).