Bearing surface: body length vs. base-to-ogive

[memilanuk]

Just curious... why one way vs the other?

As far as I know, the Buhay tool (and its clones/derivatives such as the Tubb BSC, Mark King's version, Hoover/Accuracy One, etc.) have a top and bottom comparator body, and measure (approximately) the length of the bearing surface, under the premise that variations in the bearing surface i.e. body length would affect the in-bore pressure, and thus velocity. Various people use a pair of seating depth comparators attached to a set of calipers as a simple of the above.

What exactly is the base-to-ogive measurement supposed to achieve that the above does not, or what is it supposed to be fixing that is wrong with measuring the bearing surface as described above? The Sinclair bullet sorting stand, for example, only measures from base to ogive, and most of the methods/tools already mentioned *can* measure that way as well. My question is, why would you want to? I'm not saying it "doesn't work", just that I don't see what is gained or remedied.

TIA,

Monte

 

[johara1]

Bearing surface and over all length.......jim

 

[necchi]

What exactly is the base-to-ogive measurement supposed to achieve that the above does not, or what is it supposed to be fixing that is wrong with measuring the bearing surface as described above?

Nothing,, as described above.

It's simply a variation of a measurement. Notice I didn't say they measured exactly the same thing.
The only difference is the diameter of the holes used in measurement.

Both are tools that can be used to separate bullets into categories of measurement within any given lot.
The Ogive measurement will help me determine seating in relation to the chamber and bore. A Bullet bearing surface measurement alone won't let me do that.

If I was an anal bench shooter, I'd measure by bearing surface then length. I might get 30 bullets out of 100 that matched.

 

[memilanuk]

The Ogive measurement will help me determine seating in relation to the chamber and bore. A Bullet bearing surface measurement alone won't let me do that.

Okay, that right there is something I have problems with. Not you specifically, because I see that repeated from time to time on different forums, so please don't take it personally. Either I *really* don't understand how bullet seating works, or I'm seriously mis-reading whats being said. Wouldn't be the first time, for sure

I have various measuring tools and fiddly things for getting the seating depth of a given bullet in relation to my chamber. They do reference off the ogive of the bullet, relative to the base of the cartridge case. But those tools, process, and intent are entirely *separate* from what I use for measuring the bearing surface - or base-to-ogive - of a bullet. Specifically, I fail to see how the base-to-ogive distance has anything to do with the seating depth. The base of the bullet doesn't *touch* anything during the seating process - which begs the question: how exactly does it help you to "determine seating in relation to the chamber"?

I can appreciate how (at least theoretically) variations in bearing surface may influence the in-bore pressure and thus muzzle velocity, or how variations in base-to-ogive length may indicate variations in bullet shape (specifically the back end) and hence BC... just as I am aware of how neck tension and/or bullet diameter can have a profound effect on bullet seating depth. Unless you are drawing some sort of corollary between base-to-ogive measurement and bullet diameter (or *ogive* shape) which in turn affects seating depth... which I gotta say, sounds a bit... thin... to me.

I really am trying to understand what people are referring to. Help me out here...

Thanks,

Monte

 

[necchi]

Hhmmm,

Ok, any tool we use for measurement is only valid in the hands of the person taking the measurement, and that measurement only pertains to that application and used for comparison.
I can't measure with my Hornady tools, the bullet in my hand and transfer that data directly to your rifle, it's all relative to an individual application,,Get it?

" Specifically, I fail to see how the base-to-ogive distance has anything to do with the seating depth. "
Your right, it doesn't, it's a separate measurement applied to another complete set of needs, that is independent of bullet bearing surface.

Your original post was questioning what base to ogive measurement does that bearing surface measurement doesn't as it applies to bearing surface,,
I said it does nothing.

A person CAN sort bullets with a base to ogive measurement of the bullet alone,,
that is NOT the same as measuring bearing surface.

Your kinda trying to make a relation to two separate things,,you can't they are simply not the same things.
Apples and Oranges are fruit right? Well, so are Pears,,

I'm not going to use my Hornady OAL gauge and get a Bearing Surface measurement.
I'm not going to be able to use a Bearing Surface measuring tool to check if my bullets are seated to the same depth in relation to the rifling,,
Don't work, two different things.

 

[memilanuk]

Well, like I said I thought I might be mis-reading something you said... looks like I mistook the context. Otherwise... I'd say we're on more or less the same page.

I will say, though, that I have seen, in more than one place and by what would otherwise be considered 'reputable' sources, statements to the effect of what I cited above... that they used the base-to-ogive measurement to adjust their seating depth for different sorted batches.

Anywho, thanks for the responses thus far!

Monte

 

[edlongrange]

Message from Lynn:

"Monte

When we sort bullets for bearing surface length you are correct that it helps us achieve more uniform pressures.

On the ogive to base length I will give you a wildly exaggerated example and hopefully it will help everyone see why this is just as important.

If we started out with a 1000 bullets that were all exactly 12 inches long and the bearing surface length was exactly 3 inches long on each bullet we would still need to measure base to ogive for these reasons.

If we wanted to point or tip our bullets we would want the bearing surfaces all at the same point on those 12 inch bullets.If the 3 inch bearing surface on one bullet was 1 inch from the heel and on another bullet it was 2 inches from the bullets heel your meplat trimmer would make contact at two totally different locations and your meplat diameters would vary ruining BC.

Next if the bearing surfaces were not at the same location on each bullet eiven though they were the same length you would have variations on the amount of bullet inside of each neck which would defeat the whole purpose of measuring bearing surfaces in the first place.

Lastly if the bearing surfaces were equal in length but not in there location on the bullet our stability/balance point would vary bullet to bullet. Picture one bullet with a very long ogive length and another with a very short ogive length.

Lynn"

 

[necchi]

I think part of the trouble is folks think all bullets are exactly the same, that somehow each bullet is machined to an exact specification.
And while they are to a certain extent, there still is a tolerance of +/- that machines are capable of producing in a profitable manner.
Even the ogive curve as it's rolled off a die has a variable that's not exact as the previous one

With no disrespect intended, I think Monte is/has difficulty grasping the two different issues here,,
I look at bearing surface and base to ogive as two completely different things, where Ogive as it applies to measurement , is only a measurement I use at a random "Datum" point on the ogive to achieve similarity in my seating as it applies to the OAL of the cartridge and not the seating depth of the bullet in the neck,,
,,again that's two different things.
So we have three things happening with bullet length;
*Over all length,
*Bearing Surface Length
*And position of the Ogive curve at a select Datum point in relation to the Bearing surface.

Now if each bullet was turned by hand on a lathe by one person using the same caliper,, and anything out of specific measurement was scraped,, we would need only one device to check bullets.
But that's not the case, machines run 24hrs, usually with 3 shift changes, AND material alloy's change slightly in any given shipment of raw material. It's simply the nature of industrial manufacturing.

 

[jo191145]

I will say, though, that I have seen, in more than one place and by what would otherwise be considered 'reputable' sources, statements to the effect of what I cited above... that they used the base-to-ogive measurement to adjust their seating depth for different sorted batches.

Anywho, thanks for the responses thus far!

Monte

Monte
I'd bet we read the same article on a different forum. Twas quite a few years back now.
It suggested as you say to adjust the seating die up and down according to sorted bearing lengths. No other measurements required! Whatever the difference was adjust the seater + or - and all would be seated the same distance from the lands.
Even as a green newbie back then I threw up a flag in reference to that article and PM'd the sites main moderater asking "What the He!!". The seater die could'nt care less how long the bearing length or bearing length plus boat tail is. The variations that need to be addressed for consistent seating depth are at the other end of the bullet.
Never got a response.
I'm sure that article helped confuse a lot of shooters.

FWIW I'm not seeing anyone confused here. Or am I the confused one?

 

[DanGuy48]

Hi, new here, but this caught my interest. If the bullet is pushed far enough into the throat, it will eventually make contact with the lands, presumably near the transition of the ogive to the bearing surface. At that point, I'd back off a bit by increasing my seating depth. Assuming that all the bullets are identical, just for this example, then this would have an effect on COAL. Correct? Is that what was initially being asked perhaps?

 

[memilanuk]

jo191145,

Seen it in a few posts on various forums, and specifically in the comments for a post over on Sinclair International's Reloading Blog. That one is about two years old... but pretty much exactly what you describe:

The ogive to base measurement is giving the reloader more consistency in seating depth and bullet jump.

and...

...the base to ogive measurement is the most important... you should do this so you can adjust your seating die stem for each group so all your bullets are seated the same distance on or off the lands in your ‘sweet spot”.

necchi,

Yes, I understand the ogive is a region, not a specific point, and we are measuring from different datum points on that region. The datum on the ogive that my seater contacts is not the same as the datum on the ogive that my comparator(s) touch, etc. Perfectly clear on that

lynn (by way of ed),

I understand what you're saying, about the length of the bearing surface vs. the location of the bearing surface and its effect on BC. It almost sounds as though you are advocating sorting by *both* dimensions?

 

[memilanuk]

FWIW, in the process of doing more digging, I found some more information in Sinclair International's Reloading Blog, this time citing Bryan Litz as the source:

Another question arose about base to ogive sorting, and if sorting by bullet bearing surface (boat-tail junction “pressure ring, or heel” to ogive with the use of two comparators) was more critical in terminal performance of the bullet. I spoke with Bryan Litz, author of “Applied Ballistics for Long range Shooting”, and lead ballistician for Berger Bullets. Bryan informed me that the most critical measurement in bullet sorting for consistency is in fact the base to ogive measurement. According to Litz, this measurement is in fact sorting the bullets for consistent Ballistic Coefficients (BC). What occurs in the bullet forming process is what determines the bullets physical ballistic qualities. When a bullet is forced into the forming die a few factors come in to place to determine the outcome. These factors include the amount of lubrication used and how it can change the force exerted on the bullet when being formed. If the bullet is forced further than it should into the die, the outcome is a bullet with a short bearing surface, long ogive, and narrow meplat. If not forced far enough, the result is the opposite, long bearing surface, short ogive, and wide meplat. This is why variations are found in bullets, and by sorting them by the base to ogive you are sorting by the best method available. Measuring the bearing surface makes sense, but Litz has found through experimentation more inconsistent results with this method. He explained that if you look at the pressure ring of a bullet under magnification there are inconsistencies that resemble a wavy line. The heel of a bullet is not a repeatable surface like the bullet’s ogive, and these inconsistencies will cause varied measurements. Most would think that the bearing surface variants of a bullets would affect velocity spreads, but Litz claims that that factor is “down on the list”, and in tests showed little if any effect.

I guess that pretty much answers my question...

 

[jo191145]

Well Monte, either they have wrapped their head around something I fail to grasp or they're just plain nuts.
As a shortranger I refuse to sort bullets. Consistent DTL is all I care about. If bullet A won't shoot with consistent seating depths I'll move on to bullet B.
OK, I have a few LR rigs but they're just toys to me. No competition. Pretty much the same attitude tho. If A requires sorting due to huge variations I'll buy some B and look for better.

Anyhow glad you got the answer to the original question.

 

[jo191145]

Donovan
You obviously know the answer to your question.
Of course there can be variations in the ogive.
I've also seen lots of LR bullets that measured .040" difference using two comparators.
While not a sophisticted optical comparator you know theres trouble there.

PS The only reason I began measuring was because I was seeing .005" variations in seating depth using a comparator.
The trouble was everywhere. They're still sorted and for the most part unshot.

 

[necchi]

Another good point Donovan,
To get a true "bearing surface" measurement, wouldn't a person have to slug the bore for an actual dimension, then use tools that have that exact diameter to check how much of a given bullets surface IS actually bearing on the bore?

See? That's just it. The tools we use are provided with an insert that has a diameter,what we measure with either the Bearing Surface or Ogive/OAL tool is just what that diameter insert allows us to measure.
There is nothing carved in stone that states we must never make a change to that inserts diameter. What's wrong with drilling it out to the diameter we need?

FWIW, the Hornady OAL gauge doesn't measure Ogive.
It stops at a datum on any Ogive a bullet has at the inserts diameter, that measurement is worthless by itself. It's only used as comparison to other bullets.

 

[jdb]

Bob Greens custom shop is now offering one of the most interesting accuracy enhancing products to come along in some time. The B.G.C. Bullet Comparator. This new design came about as a result of customers seeking to understand why different lots of bullets would not shoot as well as others. What we found was, especially regarding VLD bullets, the point on the bullet where the bullet seater makes contact and the point on the bullet where the lands make contact would vary from bullet-to-bullet and from lot-to-lot. With this device you are able to sort bullets into sub-lots, therefore keeping the loaded rounds seating depth very consistent in seating depth without constantly changing your bullet seater. The results have been outstanding. Shooters have cut their group sizes in half without flyers.


We now offer 6mm, 6.5mm and 308 calibers with or without .0001 indicators. One indicator will fit all comparators, eliminating the need for multi indicators, keeping comparators cost effective.
go to: greensrifles.com & click new products

 

[mikecr]

The BGC does work well to qualify ogive radius, and therefore much of the datum variance plaguing sound measurements in discussion.

I don't personally assign any value to bearing in itself. I believe it's measure, by itself, is a wasted and meaningless effort.
IMO, the biggest gains in bullet measure lead to uniforming meplat diameters.
But meplat uniformers are not. They are merely nose trimmers..
To take meplats to any standard diameter, means setting of a standard datum on noses, and ogives must first be qualified to do so.
This, and other bullet measure relying on a nose datum, is where a BGC comes into play.

 

[edlongrange]

Reply for Lynn

"Monte:

Absolutely YES you need to make both measurements.What good would perfect bearing surfaces do us if they were located in different points along our axis?

Lets say all 1000 bullets were absolutely 100% perfect for bearing surface but the location of the bearing surface varied by +/- 0.005. We now seat all of them so they have the same exact length.

Tell me what just happened to our cases volume with 0.010 total variation in the location of the bullets heel?

Every bullet made even off the same die is inconsistent from the next bullet.To win matches you want them all as close as is possible. No matter what type of tool you are using if your getting variations you need to segregate them into like groupings. Variances regardless of location are just that variances.

Lynn."

 

[memilanuk]

Lynn (via ed),

What percentage improvement would you say would come from sorting by bearing surface on top of base-to-ogive? I'm all for 'better', but at some point I'm willing to settle for 'good enough' vs. 'perfect'.

Thanks,

Monte

 

[Leaddog]

Monte - I'm with what Bryan Litz said. If anyone knows bullets, he's the guy. I gave up on bearing surface measurements a long time ago.

Perhaps Bryan could join the conversation?