Base to ogive lenght

[liseo]

Hello guys

I have one question, and hope you all undestand my terrible english.

When I sort my 6 BR bullets for ogive to base lenght, , I find as much variation as .008".

If in reloading test my best results are with "XX" distance to land using one group of sorted bullets with same base to ogive lenght, when using another lot with say shorter lenght, the correct thing to do is adjust the seater die, in this case assembling the round longer the same amount who are the difference in the base to ogive lenght?
Sorry my english and thanks.

Liseo

 

[fdshuster]

Liseo: You did not say what 6mm bullets you are using. If they are one of the mass produced brands, like Sierra, then yes, I have also found differences in base to ogive lengths, sometimes more than the .008" that you've found. I can open a factory sealed box ( the 107 SMK, for example), and after sorting them will have 3 or 4 different groups. But, I can take a sample of 5 from each group and load a box of 20 rounds, without changing the bullet seater depth adjustment, then measure case head to ogive lengths and they will all be identical. All 20 seated bullets will be contacting the leade by the same amount. The length difference is in the case neck, how deep the base is into the case. Does that difference matter as it relates to accuracy? I can't answer that, but have never been able to prove it one way or another. When opening a box of Berger bullets ( for example) and measuring the base to ogive differences, there basically is no difference, even when going from one lot to another. One of the benefits ( I guess) of the extra cost of the Berger, Barts, Fowler, etc. bullets. This issue has been raised on this site before and several of us have suggested that some bullet makers have more than one machine making the same bullet (type), then funneling them all into one collection point at the end of the line, but others closely connected to the bullet making industry have denied any reputable manufacturer would do this. But, the question of why the differences remains.

 

[glo]

Yes, the correct thing to do is adjust the seater die.

I doubt the difference in seating depth of + or - .004" on an extream spread of .008" will effect accuracy. That is if you separate out each group of bullets into their own lots. Only chronographing will tell, but I bet there is not much of an average velocity change either.

 

[necchi]

And I'll respectfully differ just for the discussion.

The difference is in the length from ogive to base, thus the variable will be the tiny amount in bearing surface of the bullet to the barrel.

Adjusting the seating to change how much of the bullet is in the neck will not change the bullets bearing surface. It may effect case pressure slightly.

I have seen some amazing groups from Gents that sort bullets and shoot groups with only a given group of similar bullets,,
,, but I don't think changing seating will help the mixed batch of all bullets.

 

[liseo]

The bullets in question is the SMK 107 grains.

My guess is that the best thing to do is to sort the bullets and shot those who have the same base to ogive lenght, not because one will have more bearing surface than other, but because this big difference ( .008") will affect how much one will be far from the lands than other. Seems to me that when fine tuning in reloading, sometimes even .005" difference from the lands could affect the groups size. I just bought my Sinclair bullet comparator and i´m trying to find its utility.
But if we dont assemble the ammunition in different batch by ogive to base lenght, which is the usefulness for this step?
I am here to learn, so any help is welcome.

Thanks

 

[fdshuster]

Liseo: I agree with everything the other posters have said. These manufacturing differences in bullet dimensions are not ideal for the maximum accuracy we expect, and everything we can do to level the playing field has to be an advantage. But, if you will re-read my post you will see that I specifically mention that I can take bullets of different base to ogive lengths and load them all using the same seater die setting, then measure from the base of the case to the ogive, ( using the same type of bullet comparator as your Sinclair), and all those dimensions will be identical. Each & every bullet has the same contact with the rifling in the leade area. It's up to you to decide if it's important enough to seperate the bullets according to lengths & keep them seperated thru the loading & firing. Try it yourself: pick 20 bullets with different base to ogive lengths & load them without making any changes on the seater die, then measure the lengths from the base of the case to the ogive & I'll bet they will all be the same. I've been told by several of the before mentioned who are closely related to the manufacture of these bullets that it is their belief that differences in these lengths does not matter. This was their response when I questioned them as to why we have these differences. They never did answer my question of why the different lengths are so common, especially when they claim that they are all made on the same machinery with the same forming dies. I guess it's up to us to decide how important this whole issue is. Some I know do not care, others are concerned enough to sort & load them seperately.

 

[mikecr]

Liseo you, and glo, have things all mixed up.
Your die will seat them all the same distance to the lands regardless of bearing or base variances.
You can not adjust seating distance to lands to compensate for any of this(it doesn't).
And you'd just be adding another variable.

Now the variance could be ogive radius, or difficult tangent radius measurement, but again the seater will still seat them to the same distance from lands.
The little bit of more or less bullet body in the neck cannot be proven meaningful, given inherent tension variances already there.

 

[guidom]

i know what you mean. i have found .060 in my sierra bullets

 

[liseo]

So, the Sinclair bullet sorting stand measure the base to the point where the bullets meet the barrel rifling ( or I am wrong?)
I cant understand how this difference will not affect the distance from the ogive to the rifling. I ain´t saying that this difference has influence in how the rifle will shoot ( at least I will not see, as I am a so so shooter).

Soon I will order with Sinclair the tool to measure the ogive to the base of the case, in ammunition assembled with different ogive to base bullets, just to check.

I think i´m more confused than ever...

Thanks for your patience with me :-[

 

[alf]

Also, the base to ogive measurement does not take into account the possible measurement differences in the base to boatail/body juncture, which is why some measure only the bearing surface, and sort accordingly.

Then the wind blows 40 MPH...........

 

[zipollini]

I would think that sorting bullets by weight and bearing surface would be enough.

Bearing surface comparator - http://www.davidtubb.com/bearing-surface-comparator-inserts-not-included

Article about measuring bearing surface - http://www.accurateshooter.com/gear-reviews/bearing-surface-comparator/

 

[fdshuster]

liseo: While differences in length exist from the base of the bullet to the ogive point of contact on the measuring gauge, that specific point on the ogive never changes. The differences consist of a "longer" bullet bearing surface and that's the part that hangs lower into the case. if taken to the extremes the bullet would be hanging down into the case powder area well below the neck/shoulder junction. What these bullets do all have in common though is uniform ogive contours/ they are identical in the shape of their nose, and because of that the seating stem contacts each & every one at the exact same location on the bullets ogive. As another example comparing the 107 SMK that we are both using with the 95 SMK: When I take measurements of both to touch the lands, they have identical measurements, the difference being that the 107's sit deeper into the case neck than do the shorter 95's. Try it yourself, as I suggested earlier & load up 20 using a mix of bullet lengths, then take the length measurements.

 

[6BRinNZ]

Liseo,

Have a read of this article, it should clarify most of your questions about the process and why seating depths vary etc etc.

http://riflemansjournal.blogspot.com/2010/09/reloading-measuring-bullets.html

Basically

1./ Sort bullets by base to ogive - to make yourself feel better (I do this and I feel better)

2./ Measure base of case to ogive of a loaded round - to determine if seating depth is consistent (i.e ogive to lands consistency). Lots of factors affect this consistency - neck tension, type of press and dies, bullet shape, speed with which bullet is seated...the list goes on.

Good luck

 

[necchi]

I cant understand how this difference will not affect the distance from the ogive to the rifling.

First, The bullet ogive is not a specific place on the bullet.
The spot on the bullet that your Sinclair selects it's is by contact, it will contact all of your bullets in the same place by diameter,,, this select place of the bullets diameter is simply referred too as the magic "ogive" spot,,,

Your dies seating stem also contacts your bullet at a certain place by diameter.
The seating stems place of contact, may or may not be the exact same place as the Sinclair tool because of a different diameter of the tool. Both places of contact, for each tool is still called the "ogive".

Ogive,, is really a mythical place on the bullet that only pertains to the tools the individual is using with the bullet he's measuring, and that measurement is only usefull too that person at that time,,,

Now, Your seating stem is going to push the bullet into the neck of the case using it's contact point on the bullet no matter how much bullet is underneath that point,,
,, the "ogive" point to the lands won't change,, the depth of the bullet in the case will.

 

[liseo]

OK, guys, I believe I got it ;D

The bullet portion where the bearing surface finish and begins the ogive to form the tip is always the same dimension, so the difference is in the bearing surface lenght.
If one bullet is .008" shorter with the bullet comparator, this mean that this bullet still will have the same distance from the lands that other longer, but the base of the bullet will be .008" less deep in the neck.

Thanks to all of you who had the patience to explain.

 

[fdshuster]

Yes, you got it. And necchi cleared up a point I failed to make: the point on the ogive is only a reference point, based on the dimension(s) of the particular measuring tool you are using. The same as headspace length taken from the base of the case head to a reference point somewhere on the shoulder of the case. As long as you are using the same tool for all measurements, they are all valid numbers. Excellent article by German Salazar, as usual.