Ogive differences

C

cdoc42

New member
I think it's pretty common knowledge that the ogive on 2 bullets of the same weight and caliber, but different manufacturers differ, so seating to equal overall lengths from the base of the case to the tip of the bullet is not the most exact way to look for accuracy. I have also had the experience where the ogive position changed in a new box of 150gr Hornady SP .270 bullets compared to a previous box I had on hand. I caught it because the cannelure was in a different position.

Anyway, the current thought came about when I shot my 6.5 Creedmoor with Sierra 140gr SBT and Hornady 140gr SP, both loaded with 40gr of H4350 and seated at 0.015" from the leade.

Both 5-shot groups at 100 yards were less than 1 inch, but the Sierras landed 0.6" above my point of aim while the Hornady bullets landed 1.5" high.

I measured each bullet with a comparator to see what the difference was in the position of the ogive:

Sierra OAL base to tip = 1.258" Base to ogive = 0.779" Therefore, tip to ogive is 0.479"

Hornady OAL base to tip = 1.252" Base to ogive = 0.734"; tip to ogive = 0.518"

On this basis, the Hornady bullet has 59%, while the Sierra bullet has 62%, of their respective weights behind the ogive.

Would that be enough to explain the difference in the point of impact?
 
I am not much on the theory end of this but I do adjust my groups using seating depth than powder charge. Play with the seating on any give charge and you can make the group go from horizontal to round to vertical. Maybe one of the theorists here can shed more light, interesting thread though
 
Test both again. If results are different, then your rifle wasn't held and fired the same way for each load.
 
44 AMP:My understanding of "ogive" is that point on the bullet that engages the rifling.

Bart B: I will do that but when I fire my rifles I'm certain that the front rest is in exactly the same position for each shot, and that the front of the stock touches a vertical post at the front end of the rest. I try to avoid canting the rifle by having my targets posted using a level, allowing me to use horizontal and vertical points to match the reticle. Finger placement is the center of the second finger pad and I take a "deep" breath and slowly exhale, planning to have enough pressure exerted on the trigger to fire at the end of exhalation. I'm not sure what other variables I'm missing.
 
44 AMP:My understanding of "ogive" is that point on the bullet that engages the rifling.
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Speer defines ogive as "the curved portion of a bullet ahead of the cylindrical, or shank section. Also the radius of this curve, usually expressed in calibers."

Hornady says ogive is the curve of the bullet's forward part. And also uses the terms secant ogive and tangent ogive to express whether the ogive is a slope or a curve.

Those were just the two within reach. Other bullet makers have similar definitions, all referring to the portion of the bullet from the point it begins to taper, or curve down from full caliber diameter to the tip.

It is not a point, it is section of the bullet's length. The entire length of that section is the ogive.

The specific portion of the bullet that first touches the rifling is not the ogive, it is a point on the ogive, which will differ in distance from the base of the bullet, and also from the point where the ogive begins, depending on the curve or slope of the bullet's design and the exact point it touches the rifling, which can be, and usually is slightly different in each different barrel.

when I hear "measured to the ogive" my first thought is always "where on the ogive???"

Thank you for explain what you meant by ogive. Am not saying you're wrong, only that your definition is different from the one used by the people who make bullets, and a lot of the rest of us.
 
Cdoc42, if the rifle's buttplate is held lower in your shoulder, the shots will go high.

44AMP, there is no common term for the throat (or leade) touch point on bullet's ogive. It varies for a given caliber depending on throat and bullet diameters and shapes. It's typically about. 002" smaller than the barrel's groove diameter. It erodes further down the barrel. 001" every X shots; moreso with over bore capacity cartridges. There's no standard for the transition from under bore to over bore.
 
From that I gather the official definition of ogive is not the point on the bullet that engages the rifling, but it includes the section that follows that point all the way to the base of the bullet, or to the point where the boat tail begins to taper.

From a practical standpoint, however, are we not seating bullets some distance from the portion of the bullet that first engages the rifling? Isn't that the same point that engages the comparator?

What word is best used to identify the point on the ogive that first engages the rifling?
 
BartB: "Cdoc42, if the rifle's buttplate is held lower in your shoulder, the shots will go high."

I can see where that would play a part, but wouldn't it be unusual to hold the rifle in a given position for 5 shots that deliver a 1-inch group, followed by an inadvertent different shoulder position for the next 5 shots with a different bullet that also deliver a 1-inch group? I would think that explains flyers, but I just wondered if the difference in weight distribution in bullets of the same weight and caliber plays a role in trajectory.
 
Do you have access to a chronograph? It would be interesting to see the muzzle velocity of each of these loadings. There may be differences in the engraving force for the Sierra vs the Hornady bullets.
 
Ya I agree, a chronograph might show you something, have you shot this same loads and bullets side by side before? if so did they land in the same spot at 100 yds last time. They are not the same bullet so the bc or something in the difference mite account for where they landed.
 
The "official" definition of "ogive" is in SAAMI's glossary; the curved portion of a bullet forward of the bearing surface.

Put a straight edge on the bullet bearing surface to see where the curved ogive starts. The angled throat rifling touch point on the bullet' is a couple thousandths inch smaller in bullet diameter there and several thousandths inch forward. Varies with throat angle and diameter.

As rimless bottleneck cartridges are typically hard pressed against the chamber shoulder when fired, there's space (officially termed head clearance) between bolt face and case head/base. It's the dimension from case shoulder to the bullet's OTTP (Ogive-Throat Touch Point) diameter that matters.

OTTP is my definition. 100% logical to me. Thought about using some term for case shoulder to OTTP but none worthwhile yet.
 
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Well the simple way to fix this is to choose one of the bullet's develop the load and sight it in with that load. What your doing is comparing one brand of bullet to another and that normally isn't ever gonna work. Why? I haven't a clue. I measure the OLL of the bullet with the bullet just back of the lands. Then load all of them and and run them through the chamber. One come's out with land marks on the bullet and I re-adjust the seater die for that round so the land marks are gone. Once done the whole box get's run through the seater and none of them touch the lands at that point. I don't believe measuring to the ogive really solves anything but then all I have ever been is a hunter. I'm not sure how much difference adjusting that way really makes, maybe enough to win a benchrest match? That won't mean diddly in the hunting field. I knew a guy several years ago, dead now, that swore up and down adjusting jump to the lands gave him better ammo but, he didn't adjust his hunting ammo the same! Go figure!

Had a Rem 700 Short action years ago in 6mm Rem. Magazine length wasn't long enough to seat the bullet's out where I wanted. Ended up with quite a bit of jump for the bullet's, they shot very well anyway. My favorite way to seat bullet's was base into the neck one calibre depth. Another way that has worked well for me is the base of the bullet to the intersection of the shoulder and neck. Old 7mm mag I had I used 160gr bullet's in and the lands wouldn't allow me to do that. So I seated a bullet that way in a dummy case and took it to a gunsmith and had the lands let out enough to allow the round to chamber easily. Turned out it was one of the most accurate rifles I ever owned. I am just not convinced the distance off the lands matter's as much as some thing but I also think there need's to be some small amount of jump for the bullet. All action's don't allow that for no other reason than the length of the magazine.

I think something that a lot of handloader's do today is chase one hole accuracy which I doubt they'll ever get and leave proformance cut back to get it. In my experience I've always found I didn't have to give up any performance to get much much better than hunting accuracy. Of course in a bench rest match I'd get my butt handed to me! That old 7mm mag consistently shot 160gr bullet's into 5/8th inch! No hunter using that much rifle needs that kind of accuracy, really nice to brag about though! Right now I have two 243's that run right at 1/2" group's @100yds. The odd's of being able to hit a sage rat with one of them at 300yds are about the same as using a 1/4" benchrest rifle!
 
there is no common term for the throat (or leade) touch point on bullet's ogive.
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I agree, and that is part of the problem creating confusion.

From that I gather the official definition of ogive is not the point on the bullet that engages the rifling, but it includes the section that follows that point all the way to the base of the bullet, or to the point where the boat tail begins to taper.
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I can't speak to what constitutes an "official" definition, the definition I am using is what is provided by the bullet makers, and found in their reloading manuals. Using THAT definition, the ogive does NOT include the full caliber diameter portion of the bullet. That full caliber diameter portion of the bullet is referred to as the body, or shank, or sometimes the bearing surface.
 
"...but different manufacturers..." Two bullets of the same weight by the same maker can have different ogives too. A 150 Spitzer vs an RN, for example.
"...that point on the bullet that engages the rifling..." Nope. The ogive is where the arch of the bullet starts. The ogive has nothing to do with OAL either. At least not until you have worked up the load and fiddled with the off-the-lands distance. Said distance being different for every chamber. The off-the-lands stuff is 100% optional, 100% trial and error finding it and isn't necessary unless you feel like it.
"...40gr of H4350..." Is the Max load for a 140. You work up to that or just pick it? One should not start at the Max load.
 
cdoc42 said:
wouldn't it be unusual to hold the rifle in a given position for 5 shots that deliver a 1-inch group, followed by an inadvertent different shoulder position for the next 5 shots with a different bullet that also deliver a 1-inch group?
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No, not unusual at all. If the rifle's held repeatedly the same for each round in a 5-shot group. Especially when there's typically a 3X to 4X spread across all 5-shot groups with the same stuff.
 
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ogive noun
\ ˈō-ˌjīv \
Definition of ogive
1a: a diagonal arch or rib across a Gothic vault
b: a pointed arch
2: a graph of a cumulative distribution function or a cumulative frequency distribution
3: OGEE sense 1
First Known Use of ogive
13th century, in the meaning defined at sense 1a

History and Etymology for ogive
Middle English oggif stone comprising an arch, from Middle French augive, ogive diagonal arch

https://www.merriam-webster.com/dictionary/ogive
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the gunsmithing term ogive took it's name from 1b:a pointed arch due to the shape. Base to ogive measurements will depend on a couple of things.

the skill of the person doing the measuring. Measuring takes a modicum of skill for applying consistent pressure and technique

the diameter of the comparator to establish a datum, or starting point, for the measurement. Notice in SAAMI chamber drawings the datum for a measurement is given a number such as .400. That is to let the person doing that measurement that they need to use a insert that has a hole with a diameter of .400 for that measurement. Using a datum with a hole diameter of .390 or a .410 would throw the measurement off the initial measuring point would be at a different point on the bullets ogive

and of course we have the manufacturer's tolerances. Don't expect custom quality bullets at bulk bullet prices. Bergers are pretty consistent for a mass produced bullet

been thinking more about the OP's initial post. My guess is was due to a simple positional shift of the shooter between strings. The Army's AMU unit has a sergeant whose full time job it is to test ammo and rifles and make adjustments . He has access to a 300m shooting tunnel and both machine and bench rest. When using the bench rest sitting in a chair he has stated that moving his foot three inches and changing nothing else changed the POI at the target

Accuracy: A Brief Guide to Precision Shooting

It ain't just the arrow involved here, otherwise we would all just load precise ammo and all our shots would be in the 10 ring
 
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4 people shooting the same rifle and ammo in a 4-man team match will use different sight zeros, often a 2 MOA difference.
 
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