How to measure COAL with Bullet Comparator

Unclenick said:
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:

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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.

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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.
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Which goes to show that you really do need to specify in your load records which comparator you are using (and perhaps to measure and record the inside diameter of the comparator throat where it touches the ogive). Otherwise some other poor b*****d is going to be seating their bullets to a greater or lesser depth if they try to duplicate your load.

It would of course be good to have a standard for this (e.g. "the SAAMI comparator shall touch the ogive at the point where the bullet diameter has reduced to 70% of maximum"), if we don't already. I am under the impression that the datum for case shoulders IS standardized.
 
What about SAAMI's bullet diameter tolerances of .003 inches or thereabouts?

What about the chamber throat angle and diameter tolerances.
 
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If you want to know COAL (CARTRIDGE OverAll Length)
then something that doesn't measure to both ends of the cartridge is not the right tool.

A tape measure is a poor choice for measuring diameter. You can get a rough idea but no precise accurate measurement. If you want an accurate measurement, you need to us the right measuring tool(s) for the job, and for COAL a comparator isn't it.
 
Pathdoc proposed a definition of "ogive."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."

That appears to be quite accurate and acceptable. But a definition is not really what is needed to label your handloaded cartridge length. If you seated the bullet touch the metal of the bore (as in your definition) you can't use COAL or just "cartridge length."

I have always used OAL-OG on my labels. Now, 44AMP is correct- that has no relevance or use to anyone else but me. Anyone who tries to seat the exact same bullet in their exact same caliber rifle is not likely to get the same reading because all guns are different. But my labels also say what distance I ended up with: For example, 2.155" OAl-OG = 0.015" from rifling. Now, if a reader wanted try to achieve whatever accuracy I had with that load, he needs to seat the same bullet 0.015", which may not end up in his rifle being 2.155". Now I may load 4 or 5 different weight bullets in my .270, and all of them may be 0.015" away from the rifling/leade,metal portion of the bore,etc., but they will all also be different in length. So I need to remind MYSELF they have been measured from the "ogive" and I label them OAl-OG.

Now, Unclenick's diagram opens another door. Where the shoulder ends, the ogive begins. Is it more correct to label the load 2.155", shoulder-ogive interface? Now it would be 2.155" OAl-SOI.

?????
 
Pathdoc proposed a definition of "ogive."
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I don't think we need a new definition of "ogive". The one we have has been in use a long time, and works just fine. What we need is a different term to identify that point ON the ogive where the bullet meets the rifling. (that is the point you want to use as your reference, isn't it??)

Call it something else. Call it BRCP if you want (Bullet/Rifling Contact Point) or some other term we can agree on, but DON'T call it the "ogive" because that just enhances the confusion.
 
The idea behind this whole question was to find a better way to get a consistent overall length of every cartridge.
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1) What is "consistent overall length of every cartridge"? Until we have a consistent definition of the terminology we do not have a destination. We do not know where we are going.

"Cartridge overall length " is from case head to meplat. Period.

2)You can load two 7.62 NATO rounds to measure the same 2.800 Cartridge Overall Length using two different bullets,one a 220 gr round nose and the other a 175 gr VLD. .From case head to meplat they will both measure 2.800.

They will not be the same distance "off the lands" . Not even close. But they are still the same 2.800 cartridge overall length. Those are different destinations.
They are based on different landmarks. Period.

3) The way bullets are manufactured ,meplats vary. The way SOME fastidious handloaders overcome this issue is they use a Sinclair (or other) "Bullet Meplat Uniformer tool" Which is fine.

4) The meplat IS by definition,one end of the "Cartridge Overall Length" dimension or measurement.
But the meplat does not contact the bullet seating punch. And the meplat does not contact the lands of the rifling.

5) If we want to get from Cheyenne,Wyoming to Dallas,Texas, Why would we buy a plane ticket to Boston,Mass? The language you use to define your destination matters ....no matter what you intend ,the words you choose convey the meaning. Ask for a ticket to Boston,your plane will not land in Dallas. Measring or talking about "Cartridge Overall Length " will get you from the case head to the meplat. There is no stopover at the rifling .

6) Your comparator attachment to your calipers gives you a landmark to measure change.
Your seater punch actually controls what circle on the ogive determines seating depth. But your seating punch is not the comparator or the rifling leade.

What is the point of it all? Better handloads? Better accuracy? Or tech talk jargon ,coffee drinking,and subsequent bladder draining competition?

Or do we come here ,ask a question because we want to learn something?

If we want to learn something,the first step is accepting that there is something we have wrong.

The next step is identifying what it is we have wrong.

And the obstacle to overcome is the ego which fights to preserve the status quo of our error.
 
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HiBC said:
But the meplat does not contact the bullet seating punch.
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To nitpick:

It does in a few particular cases, those being the wadcutter (where the entire bullet is the meplat, and it does engage the rifling) and the various broad flatnoses used for tubular-magazine rifles.

In addition, SOME round-nosed bullets are sufficiently blunt that they will not enter the cup of the bullet seater, and there the meplat (inasmuch as it exists) definitely contacts the punch.

That being said, I can't see this affecting the vast majority of modern centrefire specialist target cartridges, although the blackpowder cartridge revivalists might be shooting bullets blunt enough to have this problem.
 
To nitpick:
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I edited this post for civility.

While post 47 does offer some points that may be true, I fail to see how it advances the discussion.

What was the intent of the post?
 
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From SAAMI's glossary....

"OGIVE
The curved portion of a bullet forward of the bearing surface."

It's not a good idea for us to change it to anything else.
 
Bart B. said:
Unclenick, I'm confused. How can a bullet touch the rifling at groove diameter when there's no lands there?
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It's where contact begins, right where the conical taper of the throat angle at the breech end of the lands meets the groove diameter. The secant ogive bullets frequently have the radius of the ogive commence at an angle steeper than the chamber's throat angle. See the exaggerated image, below.

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@UNCLENICK,

Which Would be better for our M1s? A Tangent or Secant Ogive? I cant remember if the original M2 Ball projectile were Tangent or Secant, Im thinking more it had a Secant.
 
It's an interesting thing. The tangent ogive bullets seem to center better by making contact further in. They get more initial contact area that way. I think this is why Berger came up with the hybrid ogive that starts out tangent off the shoulder, then switches to secant for a higher BC after the tangent portion is narrower than the bore diameter.


Akinswi,

I'm not aware of any secant ogive military bullets unless they have some now for special sniping systems. The rest have all been tangent ogive, and tangent ogives tend to be the least fussy for accuracy loading for service rifle match ranges.
 
Akinswi,

I doubt you'll see any difference in service grade 30-06 Garands.

Maybe a tiny difference in the very best match grade 7.62 NATO Garands with commercial match barrels.
 
Bart B,

so basically with throat erosion and the limited enbloc clip length the M1 has to work with the Jump doesnt matter because we are not loading it thousandths from the lands? Or do you just load all your match ammo to max 3.340. I have also wondered with bullet Jump if there is a correlation with concentricity and accuracy .

I saw a video by Erik Cortina and he doesn’t even worry about concentricity but again he is using a bench rifle and I wonder the reason why runn out doesnt effect him is because bullet jump is way less than in service rifle
 
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Akinswi,

My handloads for Garands had bullets seated with no less than .015 inch off the lands.

Never saw any accuracy issues with varying jump to the lands distance. Zeros typically changed, though.

New cases always had best accuracy; none of the military teams winning and setting records reloaded their fired cases. The service rifle's bolt faces were never squared up like the best bolt action match rifles have.
 
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