View Full Version : Rookie question

12-23-2007, 07:49 PM
The guys at ar15.com couldn't really help me with this one, and I know it isnt bench rest related...but....

I was doing some seating depth recording using various weights and manufacturings of bullets, from 55 gr V-Max up to 90 gr. SMKs. Now I have some results which I dont understand...

All of my OAL from case head to ogave are different from bullet brand to bullet brand, the only 2 that were constant were the 69 gr. HPBTs from Nosler and Sierra. All others vary....

Why is this so? I would think that a bullet could only go so far down the throat of a chamber before it contacts the lands, at the ogave...right?

So why is it that when I measure the ogave on all these diffent bullets, that the Case head to ogave measurment is different?

Thanks, Waldo

Mike Swartz
12-23-2007, 07:55 PM
Because the shape of the bullets are different. That is to say, the point on the bullet that contacts the land occurs at a different location from bullet to bullet due to differing ogive numbers. Nothing unusual about that. What you refer to as"measuring the ogive" is a misnomer. What you are doing with an ogive comparator is comparing one bullet shape with another. Ogive is expressed in bullet diameters. A very pointed bullet either has a high ogive number or a non-tangent form. Low ogive numbers tend to be less pointy. To actually measure the shape of a bullet requires an optical comparator. A Stoney Point/Hornady or Sinclair oggive comparator actually measure from the base of a loaded round to a plane through the bullet formed by where the hole in the tool contacts the bullet form. This is simply a number and doesn't indicate anything about the form of the bullet exccept that some shapes differ. The tool allows you to reproduce a bullet seating by setting the seater to produce the same number, nothing more.

Mike Swartz