Ogive to BC relationship??

[Ogre6br]

HI
Can somebody explain what the Ogive is and how it relates to BC??

Why does a X weight 6 Ogive bullet have a lower BC than an 8 Ogive version??

Which 6mm bullet would be better a 75 grain FBHP 7 ogive or a 75 grain FBHP 10 ogive.

Thanks

later
P

 

[liljoebrshooter]

I think you have that backwards Donovan. The higher BC the pointier the bullet. Some of the VLD bullets are 12 ogive or more, the normal FB bullets are around a 7 ogive.

JOe

 

[Cheechako]

doze

This is getting very confusing to you, I'm sure. Let me take a stab at it from an ignorant farm-boy perspective. ,I'm the ignorant farm boy, not you.)

The ogive is the curved portion of the bullet body. The curvature radius is measured in calibers rather than inches or decimals. A 22 caliber bullet with a 7 ogive will have a curvature radius of 22 times 7, or 1.57 inches more or less. A 30 caliber bullet with a 7 ogive will have a curvature radius of 30 times 7, or 2.15 inches more or less. Two bullets, two calibers, two weights, two different curvature radii, same ogive. The higher the ogive number the "pointier" the bullet will be and the higher the BC will be.

The BC is the measure of a bullets ability to overcome air resistance and the ogive is but one of the inputs. A 22 bullet with a BC of 450 will have exactly the same ability to overcome air resistance as a 30 caliber bullet with a BC of 450, or any caliber bullet with a BC of 450 for that matter. The caliber or weight of a bullet are not factors in calculating an exterior ballistic chart. It doesn't seem logical but Mother nature says so and we can't argue with her. Well, we can argue but we can't win.

Ray

 

[sparker]

Ogive shape as well as length play roles in the drag form. Research has shown that the minimum drag form nose shape for a given axial length occurs with a secant ogive where the generating radius length is twice that of the tangent generating radius length for the same axial length. As the axial length gets longer, the ballistic advantage of the secant ogive over the tangent ogive decreases. Ogive length is a better predictor of ballistic efficiency with at least one caveat: the meplat must be sufficiently small as to keep the frontal drag dependent on the ogive length and shape.

Another thing to keep in mind is that as the ogive gets longer, more lead is going to be forced up into it. Henry Childs has pointed out the dangerous consequences to bullet survival that this situation causes. In general for a given bullet weight, the longer the ogive, the longer the corresponding bearing length required for bullet reliability. If more explanation is needed feel free to post with questions or email me.

Scott Parker
Bakersfield CA