7 vs 10 ogive

[46490]

I have tried to find the explanation of the differences between 7 and 10 ogive for 118 gr 30 cal bullets. How do you tell which ones you have and the pros and cons of each? Do you seat them differently - jam or not - just trying to understand the reasons and advantages of each.

 

[Chiquita]

Curious what a 7 & 10 ogive is?

 

[jelenko]

I found this post that talks about characterizing ogives by their 'pointiness'
https://forum.accurateshooter.com/threads/can-somebody-explain-ogive-numbers-to-me-eg-7-10.4002597/

 

[mike mccormick]

It is my understanding( could be wrong), that it is the radius of the curvature expressed in multiples of bore diameter. For example, a 7 ogive, 30 caliber bullet would have a curvature radius of 7× .308"= 2.155" radius. The higher the number, the pointier the bullet

 

[mikecr]

Neither 7 nor 10 would have a high BC. I imagine they're for short range BR (30br).
7 ogive would likely have a lower twist requirement while adding a bit of wind drift over the 10 ogive.
The choice could come down to the actual twist of your barrels.

I also imagine a 30br would reward high starting pressures, so testing would probably put you close to or into lands.

 

[pintopete]

Ballistics Linguistics: Bullet “Caliber of Ogive” Defined « Daily Bulletin

This article, which originally appeared in the Sierra Bullets Blog, provides a new terminology that helps describe the geometry of bullets. Once you understand the meaning of Caliber(s) of Ogive, you can quickly evaluate potential bullet performance by compari...

bulletin.accurateshooter.com

 

[Doom]

In most cases, if the bullet weight and caliber are the same, the longer bullet will have the larger ogive value. However, if the boattail is significantly different this may not be the case.

 

[6ShotsOr5?]

Neither 7 nor 10 would have a high BC. I imagine they're for short range BR (30br).
7 ogive would likely have a lower twist requirement while adding a bit of wind drift over the 10 ogive.
The choice could come down to the actual twist of your barrels.

I also imagine a 30br would reward high starting pressures, so testing would probably put you close to or into lands.

Agree the twist rate of the barrel should be sufficient for stability. Assuming sufficient twist rate of the barrel to stabilize either bullet, the chamber throating may favor one bullet vs the other one.

Someone else that used the same barrel specs and same reamer I did — not the same reamer type but literally the same reamer — told me his rifle did not like the 10 ogive bullets. Good enough for me to not test the 10 ogive bullets in my rifle.

 

[RegionRat]

Many times, it is difficult to obtain the blueprint information on the bullet design, so your question is a valid one without a well organized answer.

The book by Bryan Litz attempts to collect bullet statistics and BC values which gives some clues as to what to expect from bullets. The book gathers lots of different models and brands of bullets under one cover, so it is one of the best single resources out.

https://store.appliedballisticsllc.com/Ballistic_Performance_of_Rifle_Bullets_3rd_Edition_p/0010.htm