Ogive measurements

[longwinters]

Just got done doing some reloading for a new Sako 270 I picked up a while ago. With the 270 velocities I wanted to stick with either the Partitions or Accubonds at the ranges this rifle will probably be used while hunting whitetail.

As, seems to be, typical with the Partition 2nds the tips are somewhat inconsistent so I was going to measure by Ogive. I was surprised to find that my Ogive measurements (using my Stoney Point Comparator) were different between bullets by up to .015. I ck'd some Horny Interlocks, and some Sierra Prohunters and they were all within .003 of each other.

I have always had good accuracy with all my Nosler 2nds but this situation is a little more intolerant because of the Sako's rather short mag length. It is a real pain to have to re-adjust my seating die for every bullet to get each one right at 3.340 (yes I realize that I could load them shorter but like the longer OAL) with the dinged up points and this is what led up to my checking out the Ogive measurements looking for differences in measurements with each bullet having to be adjusted for when measureing just for OAL.

I do not have any Partition 1sts to compare against.

Is this common with all the Partitions? Or am I missing something?

Long

 

[JD338]

Long,

I don't know what kind of dies you are using but don't most seat
off the ogive? I would think that from the contact area on the ogive to the lands would be the same regardless of col. So long as you have clearence in the magazine, you should be ok.

Now I am curious, I will have to make some comparisons on factory box and seconds. Seconds are all I use, unless I run out before a hunt, and the accuracy and performance are excellent.

JD338

 

[CamoWildcat]

RCBS dies seat (push on the bullet) from just short of the plastic tip on ballistic tip bullets. I wish they pushed close to the ogive. I've checked bullets as well as loaded ammo to the ogive and overall length. Loaded ammo varies in overall length as well as to the ogive. Makes me wonder why the seating dies aren't made to seat the bullet by pushing on the ogive. Is the angle on the bullet too steep at that point?

 

[Blaine]

I was surprised to find that my Ogive measurements (using my Stoney Point Comparator) were different between bullets by up to .015. ....Long

Maybe I'm missing something. Not sure what you mean by the quote above.....from the base of the bullet to the ogive, or from the tip to the ogive? If it's from the tip, it is irrelevant what the OAL is as long as you seat based on the ogive DFL (distance from lands). Even if the seating stem seats by pressing the bullet 1/8" or so in front of the actual ogive, the difference in ogive measurements between your finished rounds should be very small. Check your finished rounds with the comparator and the measurements can't be that far off.

If the ogive to the base of the bullets are off a lot (they shouldn't be by much), it could affect ignition characteristics because you would be changing the internal volume of the case. That's mt take on it unless I'm missing something.

Blaine

 

[longwinters]

Straight from RCBS

Hi Larry, They plug seats to the ogive unless it's a full wad cutter


I should have said "cartridge" not "bullet".
I was measuring from the base of the cartridge to the ogive. Wondering if I seated each bullet to exactly 3.34 what the difference in ogive measurement would be.

Long

 

[rick smith]

Long, couple of things; measure some of the unloaded bullets in the comparator and see if they are the same or very close. Check your brass, make sure it is of the same lot and has been treated the same, all shot the same number of times, sized the same, same headstamp, etc. Next I would clean inside the seating stem and check to insure the bullet tip is not making contact with the inside of the seating stem. Check the seating stem locking nut and the locking ring on the die. Have you checked the amount of sizing being done to the neck?Rick.

 

[longwinters]

Good reminders.

I keep my brass in good shape and just bump the shoulder on the case when resizing.

My primers are seated to a consistent depth.

I reload several different bullet manufacturers (although I always lean to Nosler products) and do not have the inconsistency with the other name brands using the same brass, primer, die etc....

The only thing that is different is the bullets.

That is why I wondered about 1st run vs. 2nds.

Long

 

[Ol` Joe]

I`ve had trouble with the seating cup not being deep enough to allow the rim of the seater to rest on the bullet ogive. The result was varying cartridge OAL. The problem was always with plastic tipped bullets though, and the tips were bottoming out in the seater. I ended up drilling the seater a little deeper with a dremal tool and small drill bit then polishing the edge of the seater to insure there were no burrs. This was with both Redding and RCBS dies.

 

[Blaine]

I`ve had trouble with the seating cup not being deep enough to allow the rim of the seater to rest on the bullet ogive. The result was varying cartridge OAL. The problem was always with plastic tipped bullets though, and the tips were bottoming out in the seater. I ended up drilling the seater a little deeper with a dremal tool and small drill bit then polishing the edge of the seater to insure there were no burrs. This was with both Redding and RCBS dies.

I hear you.....I have the same problem with my Hornady and Lee dies, especially with ballistic tips, and other plastic tipped bullets. I never thought of adapting the seater stem. How did it work for you Joe, did it solve the problem of OAL variances? I'm a little leery of tampering with it before I'm very sure it will solve the "tip" problem. I have even shied away from "long and lean" noses in favor of stubbier models during load development. The best groups I have ever shot were with Sierra Pro Hunters flat base.

Blaine

 

[Ol` Joe]

Blaine the bullets seem to be seating quite evenly now. The seaters were drilled out just enough to allow the tips to enter and not touch the top of the seating "cup". It doesn`t take but a 1/10th " or so to do the trick. The seater seems to hit far enough down the ogive when the tip doesn`t interfere to keep things consistant. I don`t remember the bit size I used, as I did this over 15 year ago or so when the BT first came out and I found I had the problem. I`m guessing it was a 7/64 or 1/8".

I don`t know about Lee but Hornadies SST and V-Max are as sleek as they come, their dies should work with this type bullet since they offer them. I believe I heard RCBS will adapt their dies to fit differing tip shapes and Hornady should do the same. If I had the problem today I`d call Hornady and see if they will rework or replace the seater for you.

 

[MrFurious]

Contrairy to popular belief, most dies DO NOT seat off the ogive. In fact of all the seating dies I presently have, only the Forster Micrometer seaters actually seat off the ogive.

Lee .223 Seater Cup (0.205")

RCBS 22-250 Seater Cup (0.190")

Redding .222 Seater Cup (0.185")

 

[Ol` Joe]

Contrairy to popular belief, most dies DO NOT seat off the ogive. In fact of all the seating dies I presently have, only the Forster Micrometer seaters actually seat off the ogive

The definition I`ve heard of a bullets ogive is "the curved portion of the bullet above the full diameter shank" This on most bullets runs all the way to the tip from the shank. Weather or not this is truely the ogive, don`t know. I`ve found once one gets ~ half way or so to the full diameter area of the bullet the geometry of the bullet is quite consistant. The OAL of the bullet its self can vary greatly but drop back a couple tenths from the tip and the measurment from that point to the base will be for the most part exactly the same bullet after bullet.
I guess a more exact wording of the procedure would be to seat off the bullet flank and not the tip...........

 

[MrFurious]

It all depends on what definition of ogive you go by. When it comes to bullets, most consider the ogive as the point where the nose (cone) of the bullet stops and the shank starts. This is the point your dies need to seat off of to most accurately control your seating depth (from the lands).

From Wikipedia:

In ballistics or aerodynamics, an ogive is a pointed, curved surface used to form the approximately streamlined nose of a bullet, shell, missile or aircraft. The term ogive is also typically used to identify the area of transition between the cylindrical body of a bullet and the streamlined nose.

The traditional or secant ogive is a surface of revolution of the same curve that forms a Gothic arch; that is, a circular arc, of greater radius than the cylindrical section ("shank"), is drawn from the edge of the shank until it intercepts the axis.

If this arc is drawn so that it meets the shank at zero angle (that is, the distance of the centre of the arc from the axis, plus the radius of the shank, equals the radius of the arc), then it is called a high velocity (supersonic) rifle bullets.

The sharpness of this ogive is expressed by the ratio of its radius to the diameter of the cylinder; a value of one half being a hemispherical dome, and larger values being progressively more pointed. Values of 4 to 10 are commonly used in rifles, with 6 being the most common.

Another common ogive for bullets is the elliptical ogive. This is a curve very similar to the spitzer ogive, except that the circular arc is replaced by an ellipse defined in such a way that it meets the axis at exactly 90°. This gives a somewhat rounded nose regardless of the sharpness ratio. An elliptical ogive is normally described in terms of the ratio of the length of the ogive to the diameter of the shank. A ratio of one half would be, once again, a hemisphere. Values close to 1 are common in practice. Elliptical ogives are mainly used in pistol bullets.

Missiles and aircraft generally have much more complex ogives, such as the von Kármán ogive.

In rocketry "ogive" has become a synonym of nose cone.

 

[longwinters]

You guys never cease to impress me. Thanks

Long