How to measure COAL with Bullet Comparator

[HiBC]

"Technically the term CBTO should mean from the cartridge base to the point where the bearing surface ends and the Ogive begins."

My opinion is, that is what everyone who uses the term, "ogive," means to the user.

Is there any value in handloading to know or use the true definition of "the ogive of a bullet is the ENTIRE sloped / curved portion of the bullet from the point where it reduces down from full diameter, all the way to the tip of the bullet, which we call the meplat".

An obstacle to learning new things is to be stuck on the idea you are right.

"The compass is broke" as you confidently head deeper into the swamp.

I tend to use bullets that are better at retaining velocity. Or,bullets with higher ballistic coefficient. Those characteristics are largely defined by the base (boat tail) and the ogive. That is the part that matters to me.
I load to functional magazine length.

Unless we are single loading long,heavy for caliber bullets,in excess of magazine length, a high ballistic coefficient bullet is unikely to contact the rifling because the ogive is too skinny in most cases.

IMO,it just does not compute to think the word "ogive" implies the contact point with the rifling.

Remember,the contact diameter will be something close to bore diameter.

You said something about "CBTO" being cartridge base to end of the cylindrical bearing diameter of the bullet.
I accept that definition.That would be at full bullet diameter,which is typically about barrel groove diameter,not bore diameter.
The rifling might contact at bore diameter,or any place along the leade taper.

It would not be unusual for the difference to be about .005 on the barrel diameters.
On a tangent ogive bullet,.005 diameter might translate to significant length.

 

[lugerstew]

quote
Not at all. The BTO measurement is determined by two points. The top of the stroke on the ram and the point where the stem of the seating die contacts the bullet. Once the die is adjusted and if you use a full stroke on the press every bullet should come out the same.

I agree houndawg, that's how I load mine, but I have seen my Rockchucker seat the bullets .0005 to .001 deeper if I lean more on the handle, I'm sure my press has got some play in it from camming over too much.

 

[Bart B.]

Is the diameter of the seater touch point on the bullet the same as the chamber throat rifling bullet touch point?

 

[lugerstew]

quote:
Is the diameter of the seater touch point on the bullet the same as the chamber throat rifling bullet touch point?
Bart, I personally doubt that those two points would ever be the same, and why would it matter as long as the seater touch point, touches the ogive in a nice fit consistent manner.

 

[hounddawg]

you would think that a press that holds the die in a dieholder that has a lot of play like a Forster or a Lee Turret would have more variation in seating depths than a Rockchucker or any other single stage press. However in real life I have not seen that result.

On the turret I do not use a lot of pressure to seat. I simply raise the handle to the top and lower it. Most of the time when throwing powder and seating bullets I am sitting on a stool and operating the press with my left hand. I doubt if I am using 5 pounds of pressure on the handle. I certainly do not attempt to cam over.

If I ever get real bored I may pull my RC out and experiment with camming over, not camming over etc. However I doubt I will ever get that bored unless I get snowed in for several weeks which is doubtful considering I live way down south.

edit - Oh and Bart read my post #14

 

[44 AMP]

Is there any value in handloading to know or use the true definition of "the ogive of a bullet is the ENTIRE sloped / curved portion of the bullet from the point where it reduces down from full diameter, all the way to the tip of the bullet, which we call the meplat".

I think so. Knowing the correct "true" definition tells you when someone is misusing or misunderstanding the term. And deliberately misusing a term for convenience leads to misunderstanding and corruption of communication.

Numerous definitions clearly state that the ogive is a distance, the entire distance between two points (full bore diameter section and bullet tip) and not a single point on the bullet.

It is ironic how many people discuss very precise and technical measurements, something measured in thousandths of an inch, and yet be so cavalier and sloppy about correctly using terms to describe what they are doing.

I get it, its easy to do, but doing it wrong confuses people who are doing it correctly about exactly what it is that you mean.

To answer the question in the thread title, "how to measure COL with Bullet Comparator", the answer is simple.

You don't.

and, you can't.

Because a comparator does not measure to the tip of the bullet. And measuring from the case base to the tip of the bullet is the definition of Cartridge Overall Length. IF you are not using the bullet tip and the case base as the reference points, you are not measuring COAL, you are measuring something else.

That something else, where your bullet touches your rifling may be of use to you, but its irrelevant to the rest of us, because our rifles and our bullets are different enough from yours to make it so.

And it becomes totally meaningless when you move away from precision rifles.

Loading a specific bullet to 0.xxx" off the lands might give you an increase in accuracy but its only possible in certain firearms, not all of them by a long shot.

Turning my repeating deer rifle into a single shot in order to get that magic distance off the lands is not something I'm willing to do. I don't even do that with my varmint rifles. I load to listed book max length minus a bit, and often use a factory round to set the coarse adjustment on my seater die.

I load to fit and function through the magazine, I don't care where the bullet contacts the rifling, so long as it doesn't contact the rifling, and the loaded round works through the action. I'm not trying to get the nth degree of possible accuracy, as a friend of mine likes to say, how does that put deer/elk in my freezer with my Savage 99??

I don't "chase the lands" with my varmint rifles, either. My handloads shoot under an inch, sometimes even half that, without doing anything special, and frankly I'm not capable of using a half MOA difference in the field.

And, the whole idea of loading to just off the lands is completely useless to a revolver shooter....

You're talking about a very, very specialized technique useful in only a very small percentage of firearms and applications. When doing so, one should be precise, in both language and actions. Otherwise, what's the point??

 

[cdoc42]

There is a similarity of "miscommunication" and "misunderstanding" when a person uses the term, "heart attack." The heart is not attacking anything, and nothing is attacking the heart. The proper term is myocardial infarction, but the impropriety is ignored because the message communicated is understood anyway. So it is with "ogive." If the recipient of the message is not confused, then the communication was effective.

Again, you are absolutely correct about what “ogive” means, and your personal reloading technique avoids the need to identify a more proper term since you seat to match your magazine size. Your only concern is not jamming the bullet into the rifling, and any seating distance, in conjunction with magazine fit, is your goal.

You said, “That something else, where your bullet touches your rifling may be of use to you, but its irrelevant to the rest of us, because our rifles and our bullets are different enough from yours to make it so.”

In 44 years, any discussion I have read about bullet seating involving the use of ogive has NEVER left me with the impression that the author is telling me how to make the measurement to fit his own rifle. It has always been about a process that may provide an accuracy benefit in any gun being used, with the added caveat that the process must be repeated in that particular rifle if one chooses a different bullet.

If “ogive” is being misused, then the links I presented – LarryWillis.com, Berger, Panhandle Precision, and, at least, The Hornady Corporation, in their description of the use of the Hornady Comparator, are among the guilty.

"Hornady Lock-N-Load Bullet Comparator
Measuring cartridge lengths across the bullet tips is not a reliable (or repeatable) method for measuring loaded rounds. Its common for variations of up to .025" to exist from one round to the next. Our Bullet Comparator measures rounds from the ogive to provide consistent, precise measurements. You can also use it to check uniformity of bullets from base to ogive.

What term can you suggest should replace “ogive” that is sufficiently accurate to escape what you call miscommunication?

 

[HiBC]

I don't see a conflict there.

They ARE using the comparator to take a measurement off the ogive.

The fact that they are using a datum circle to locate where 0.xxx diameter rests on the ogive does not redefine the term "ogive".

Your measurement is useful.The theory behind it is sound.Its just the terminology is being twisted.

Suppose you are camped beside river. You push a stick into the mud exactly at the waters edge. Thats your comparator. It establishes the water's edge.

It does not measure anything.

Now,if you want your sleeping bag 8 feet above the water's edge,(or .020 off the lands)you DO have a useful point to measure from.

And,if the water rises above the stick,you know the water level is rising (or your throat is eroding)

But there is more to the river than your stick. And your stick is an indicator of change,rather than a direct measurement. It does not tell you how deep the river is.

Look at the word "Comparator" see the root"Compare"

I have used "comparators" commonly referred to as "Swede guages" that were graduated to 50 millionths of an inch. But they are not much good without the gage block set. Jo blocks. You wring together a stack of Jo blocks to the desired dimension. You set the Swede gage to the Jo blocks that rest on the flat "stage" representing a datum.

Then your Swede gage (comparator) will tell you how much your parts vary from your Jo blocks.

 

[pathdoc]

What term can you suggest should replace “ogive” that is sufficiently accurate to escape what you call miscommunication?

No term can replace it; it simply requires to be defined in a consistent and reproducible manner.

An example might be "That point along the long axis of the bullet at which the circular diameter (perpendicular to the axis) equals the diameter of the bore (as opposed to the lands)", and which is first to touch the metal of the bore when the projectile leaves the case."

 

[akinswi]

Thanks Nick , You answered my question.

 

[akinswi]

The idea behind this whole question was to find a better way to get a consistent overall length of every cartridge.

I did notice when I measured each projectile by the ogive and sorted them when i loaded those , when i measured them after using my redding competition seater die they were all within .0001 and considering my calibers tolerance is +- .001 to .002 seemed the best I could I achieve . But if i took non sorted bullets they varied alot. So in other words my cartridges weren’t “exactly the same length” if i didnt sort by ogive. But again it would still vary from tip to bottom of case head.

But after all this was it really necessary in a 68 year old M1, my answer is most emphatically no

But after shooting several groups weighing each projectile by weight instead of length seemed to render better results. In My rifle.

 

[44 AMP]

If “ogive” is being misused, then the links I presented – LarryWillis.com, Berger, Panhandle Precision, and, at least, The Hornady Corporation, in their description of the use of the Hornady Comparator, are among the guilty.

I don't know about misused, so much as incomplete. Hornady, the people who make the Comparator, use the same definition in their reloading manuals, (I checked the 3rd & 7th editions, the first ones I could easily find) and it is "the curve of a bullet's forward portion".

They aren't wrong saying they measure to the ogive, because the point they are measuring to is on the ogive, Its just not the only point on the ogive the way some people seem to refer to it as.

 

[Bart B.]

A 30 caliber barrel's bore diameter is typically .008" smaller than its groove diameter. Bore is about .300", groove about .308".

 

[Unclenick]

The devil is in the details and several details need sorting in these. First, let's sort out the terminology. Here's an illustration I put up fourteen years ago:

Ogive contact with the comparator, seating stem, or throat happens at different locations along the ogive. That fact doesn't matter, as long as you are consistent in which one you base your measuring comparisons on. However, you may want to be aware there is typically some variation in the exact shape of bullets. This accounts for Bryan Litz's observation that BC's can vary 3% among match bullets coming out of the same box. The table below shows Sierra 150-grain 30 caliber bullets I measured had about 0.008" variation in the distance of the ogive from the base, with the variation being a little greater when the measuring point on the ogive is further above the shoulder.

The problem this creates for trying to define a single diameter as the ogive contact point is in the design of bullets. Many secant ogive bullets, if their shoulder is sharp, will first meet the rifling at its groove diameter root by contacting that location with the shoulder, as the line tangent to the start of the secant ogive is often a bigger angle than the throat angle is. A tangent ogive, on the other hand, comes off the shoulder with a tangent line coincident with the bearing surface and still a very shallow angle when it meets the throat, so it will typically meet the rifling at the bore diameter, touching the corner of the rifling and throat angle. I suspect this explains why tangent ogive bullets are able to better correct small errors in bullet tilt.

 

[akinswi]

Nick,

I have seen these same variations with 168 smks aswell. I measured over 50 from same lot, and some ranged from .598 to .606 when using my Hornady Comparator .

So I tested several strings with all bullets with same measurement

.606
.605
.604
… etc

Then by weight


168.00
168.1
168.2
… etc
same brass, same trim length, powder charge, primers etc

My Rifle seemed too shoot groups better by weight vs by measuring the length of the bullet using the comparator.

 

[hounddawg]

My Rifle seemed too shoot groups better by weight vs by measuring the length of the bullet using the comparator.

that is becasue any difference in the measurement from base of the bullet to the ogive of the bullet will only cause a slight difference in the internal volume. The position of stem of the seating die stem does not change, the distance the ram raises does not change. If you had two bullets with exactly the same ogive shape and one was a half inch longer than the other and seated both without making any changes in the seating die the only difference would have 1/2 inch more bullet inside the case.

 

[Bart B.]

The best way to have all cartridge's dimension from case head to bullet tip is to have the seater stem tip ground flat so it only touches bullets there. The dimension from bullet's ogive to chamber throat may have a couple thousandths spread but that is the compromise you have to accept.

Sierra's 30 caliber 168 grain HPMK's often test under quarter MOA in their 200 yard range.

Unclenick, I'm confused. How can a bullet touch the rifling at groove diameter when there's no lands there?

 

[Don Fischer]

Bit slow these days. From what I've seen you need a caliper to use the comparator. Why not just take off the comparator and measure the thing?

 

[hounddawg]

Why not just take off the comparator and measure the thing?

that would be way too simple. I made that suggestion in post 2. That is exactly what I am doing on my .308 tactical build. I just seat the bullets to 2.795 COL to account for base to meplat variance. I am using a tuner on that rifle rather than adjusting the BTO at the reloading bench

Of course that is way too simple of a solution

@ Bart I would much rather have .001 - .003 difference in COL than .001 to .003 difference in BTO. The very last thing I would do is modify the seater stem to hit on the meplat. I could give a dar if one of my .308s is 1.995 and the next is 2.997, That will not affect accuracy in the least. Jury is still out on how much a difference .003 will make in jump but I still chase lands. That works for me and it ain't that big of a deal to check every 100 or so rounds

 

[HiBC]

Bit slow these days. From what I've seen you need a caliper to use the comparator. Why not just take off the comparator and measure the thing?

Don,if you have been following and reading the posts,that was resolved.

The OP somewhat mis titled his post. The OP is concerned that the meplats are not finshed accurately enough to give him the results he needs.

He s not measuring COAL . Its not about fitting a magazine,

As I understand it he wants to be able to have a measurement to help him control his seating depth in terms of how far he is off the lands.

That is a reasonable pursuit.

While your proposed solution will measure COAL in straight forward fashion,

this thread has been addressing the importance of using correct terminology.

And,your post takes us back to covering the same ground again.