Ogive

[Deliverator]

Okay, I've been trying to figure out how exactly one measures an Ogive radius... I don't know where to start from, and what the measurements on mould descriptions mean. 2 Ogive vs 1 Ogive, am I the only one that has no idea what that means? According to wikipedia an Ogive is a pointed curved surface, like a rocket nose cone or a bullet. To me, a radius is the distance from the outside edge to the center of a circle. An being as a bullet is a curved surface ending in a POINT it is in fact not a circle thus has no radius. The only radius I can find is from the central axis on which it will spin when leaving the muzzle to the outside edge of said bullet. And being as the line is curved this is constantly changing. So where exactly is the "Ogive" on a bullet?!

[BABore]

It is the radius on the boolits nose and starts at the tip of the nose on a pointed boolit, or end of the meplat edge on a boolit with a flat nose. It can end at a top band, start of a straight section of bore ride, a taper, or even just above the crimp groove. A 1 or 2R refers to the size of the radius based on the boolits diameter. A 1R boolit with a 0.311 diameter would have a 0.311 radius.

[Rocky Raab]

Here is a pretty good description, with drawings. http://accurateshooter.wordpress.com/2007/07/10/283/

[Cherokee]

Rocky - your web page does not work too well for me. Just FYI.

[AZ-Stew]

That page is a good overview for the average Joe, but there are a few details missing if someone wants the info for the purpose of actually designing a bullet.

The photo appears to show that the tangent ogive results in a longer bearing surface than does the secant ogive. If you look carefully, you'll also notice that the secant ogive bullet in this example has a much larger radius than the one with the tangent ogive. It is this factor that results in the secant ogive shown here having a shorter shank length.

There is also a small radius at the intersection of the boattail and the shank, and also at the intersection of the secant ogive and the shank. By definition, the tangent ogive doesn't need one at that location.

These examples are for rifle bullets. Handgun bullets and boolits aren't mentioned. The same definitions apply, but I don't recall seeing any secant ogive handgun boolit designs. there may be some jacketed bullet designs that could technically be called a secant ogive, but I'm not inclined to look them up on the vendor's web sites right now for examples.

Regards,

Stew

[Rocky Raab]

Cherokee, if the page does not display, you must be using Internet Explorer. EVERY other browser I've tested works fine. Switch to Firefox or Google Chrome - for the security they offer if not for my pages!

[Harry]

I was able to link to the site using IE 7.

[AZ-Stew]

I'm using IE-8. No problems.

Regards,

Stew

[Tom Myers]

Deliverator

The Ogive is the curved surface that makes up the nose of the bullet.

Looking at a profile of the bullet, either the top or the bottom curve will make up an arc on a circle.

The Ogive is defined as the radius of that circle divided by the diameter or caliber of the bullet.

So, if you are looking at a 0.308 caliber bullet from the side, you would see that the top of the nose is made up of part of a circle and the bottom of the nose is made up of a part of another circle of the same size.

Suppose the radius of either of those circle is 1 inch. Then the Ogive has a radius of 1 inch or 3.25 calibers ( 1 / 0.308 = 3.247)

You can use a set of calipers to measure the length of the nose, the diameter of the meplate or tip and the diameter of the junction of the body and the ogive and plug those values into a formula that will give you the radius of the ogive.

The formula is as follows:

Let D = the diameter of the base of the ogive where it joins the body.
Let T = the diameter of the tip or meplate of the ogive.
Let L = the length of the nose or ogive (Measure the length of the bullet and subtract the distance from the base to where the ogive starts to get this value)
Let R = the radius of the circle arcs that makes up the nose profile.
Let O = the ogive defined in calibers.

Then R = L x L / ( D - T ) + ( D - T ) / 4
O = R / D;

Suppose that 30 caliber bullet is 1.025" long and the body is 0.5"
long, leaving a nose that is 0.525" long with a meplate measuring 0.01" in diameter.

So:
D = 0.308"
T = 0.010"
L = 0.525"

Then

R = 0.525 x 0.525 / ( 0.308 - 0.010 ) + ( 0.308 - 0.010 ) / 4
R = 1 = the radius of the circle that defines the ogive
The ogive is defined as 1 / 0.308 or a 3.25 caliber ogive.

If you know any three of the values for that equation, you can calculate the unknown value by using a variation of the above formula

I have placed a diagram and the equations used to calculate those values on my website at the link below. Hopfully the page may help make things a little easier to understand. (be sure to pay close attention to Sqr [square] and SqRt [square root] notations when using the equations)

Tangent Ogive Calculations (http://www.uslink.net/~tom1/tech/tangent_ogive.htm)

The bullet profile can be used to estimate the G1 Ballistic coefficient of a bullet. You can plug those nose profile measurement values at the

Precision Ballistic Coefficient Estimator (http://www.uslink.net/~tom1/calcbc/calcbc.htm)

on my website. The website also shows diagrams of various jacketed and cast bullets and tips on how to measure them.

Hope this helps.