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Bullet bearing surface question

 
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  #1  
Old 10-03-2008, 05:26 PM
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Bullet bearing surface question

I have read most of the threads that cover this topic. So figured I'd give it a try. My problem is that the .277 cal insert for my comparator tool doesn't come up the the crease at the boat tail of the bullets. Is that the way I should go at it or should I use the .277 on the top for ogive and the.284 for the boat tail? The .284 seams to come just a hair past the crease. It is closer to it than the .277. For got to mention that is a 270 win.

As an aside I did sort them base to ogive already. I have 3 piles in .005 divisions. the bullets (135 smk) had a variance of .015 over 150 of them. Should I sort even further? Like every .002 Base to ogive?
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  #2  
Old 10-03-2008, 07:56 PM
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Re: Bullet bearing surface question

Quote:
Originally Posted by jmason View Post
Should I sort even further?
Yur darn right. That'll keep ya off the streets awhile. The only person on here who goes to that level of detail, that I know of, is Goodgrouper. However, his rifles do shot very well.

I've not had much luck with the SMK in the Winny. Nolser Ballistic Tips out done them every time.:confused:
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  #3  
Old 10-03-2008, 10:15 PM
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Re: Bullet bearing surface question

I don't see how typical bearing surface length variance can affect anything at all.
.005"?
It doesn't affect BC
It doesn't affect seating depth(ogive to lands) or release force(from neck)
It doesn't affect pressure

What does affect BC, is nose lengths and meplate diameters.
What affects seating depth, is ogive radius variance.

There is currently a tool out there to check radius variance. If you seat off the lands, and your gun(your accuracy) is very sensitive to the distance, the check is well worth it.

It may just be me, but it seems like measuring bearing surface/base to bearing is so common because its easiest of all checks. Just like measuring brass weight is way easier than checking H20 capacity..
Efforts that might make you feel good(and they can't hurt), but actually fail to connect with direct gains..
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  #4  
Old 10-04-2008, 04:30 AM
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Re: Bullet bearing surface question

Quote:
Originally Posted by Mikecr View Post
I don't see how typical bearing surface length variance can affect anything at all.
Quote:
Mikecr,
It's all about friction. The longer the bearing surface in a bullet the more friction when that bullet travels through the barrel; the shorter the bearing surface the lesser the friction. Remember, friction will affect pressures either going high or low. etc. etc.
.005"?
It doesn't affect BC
Quote:
Yes it does; goodgrouper has shot in the past 2 bullets with identical muzzle velocitie and 0.002" bearing surface and at 2000 yards the vertical spread was large.
It doesn't affect seating depth(ogive to lands) or release force(from neck)
It doesn't affect pressure
Quote:
Yes it does!
What does affect BC, is nose lengths and meplate diameters.
What affects seating depth, is ogive radius variance.
Quote:
Just about anything affects bc including the shape that your barrel is in!
There is currently a tool out there to check radius variance. If you seat off the lands, and your gun(your accuracy) is very sensitive to the distance, the check is well worth it.

It may just be me, but it seems like measuring bearing surface/base to bearing is so common because its easiest of all checks. Just like measuring brass weight is way easier than checking H20 capacity..
Efforts that might make you feel good(and they can't hurt), but actually fail to connect with direct gains..
Bearing surface does create many different changes that are more visible at the longer ranges.
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  #5  
Old 10-04-2008, 07:04 AM
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Re: Bullet bearing surface question

Changes in friction will change the pressure curve, velocity and vibration of the barrel.

Is it enough to notice? At long range, the beating of a butterflies wings can throw the shot off ;)

AJ
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  #6  
Old 10-05-2008, 04:05 PM
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Re: Bullet bearing surface question

No, No, it's just opposite..
.005" bearing variance could be significant to a tiny bullet on the edge of any distant performance(like a 20Vartarg at 300yds)(Hell I don't even know if a 20cal bullet has a bearing..), but amounts to absolutely NOTHING in a long range bullet..

And there are so many variables at 2kyd that it would always be a stretch to make any claims from the results. Think about it, what moa can anyone consistantly produce there? 1moa? 2moa? You think .005" of bearing variance would throw shots(in moa) so far at 100yds, or even 1000yds?
NO WAY
Well you could fire up QuickLoad, and JBM calcs, and see for yourself..

For example;
Say a 210Berger VLD has a bearing surface of .544
(.005" is nearly a 1% change)
If it's caused by reducing the nose length .005 with the same OAL, BC goes from ~.659 to ~.657
If it's caused by reducing boat tail .005 with same OAL, BC goes from ~.659 to ~.658
It's a mix, so BC might change anywhere from .001 to .002(or about 1% max)
At 1kyd the drop difference from 3kfpsMV & .002BC amounts to .3"
(thats .028moa)
I am sure your BC varies more than this -anyway-
I am also sure that any regular 1kyd shooter is working hard to cut 5 to 6" off their groups. So .3" there is probably not big on their 'things to conquer' list.

I'm not gonna lay out internal ballistics from QL, but a quick check indicates about 2fps increase from a .005 increase in bearing length with the same seating depth. I'd barely see it with 20ft screen spacing on my Oehler. But this would actually make up some of the loss in BC indicated above.
The barrel time change amounts to 1ns (Nanosecond).
If your tune requires this, you hurtin..
And there is always tungsten coating to negate all ballistic traces of this discussion.

Bearing surface checks can't hurt, unless you're doing it in place of things that really matter.
But that is what I believe is happening. I think people skip all the difficulties, condensing them down to bullet weight, or OAL, or bearing length.

Personally, I don't do it even with the best tools. Still working on that 5-6"......
[that's what she said]

Last edited by Mikecr; 10-05-2008 at 04:09 PM.
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  #7  
Old 10-05-2008, 04:28 PM
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Re: Bullet bearing surface question

Quote:
Originally Posted by Mikecr View Post
No, No, it's just opposite..
.005" bearing variance could be significant to a tiny bullet on the edge of any distant performance(like a 20Vartarg at 300yds)(Hell I don't even know if a 20cal bullet has a bearing..), but amounts to absolutely NOTHING in a long range bullet..

And there are so many variables at 2kyd that it would always be a stretch to make any claims from the results. Think about it, what moa can anyone consistantly produce there? 1moa? 2moa? You think .005" of bearing variance would throw shots(in moa) so far at 100yds, or even 1000yds?
NO WAY
Well you could fire up QuickLoad, and JBM calcs, and see for yourself..

For example;
Say a 210Berger VLD has a bearing surface of .544
(.005" is nearly a 1% change)
If it's caused by reducing the nose length .005 with the same OAL, BC goes from ~.659 to ~.657
If it's caused by reducing boat tail .005 with same OAL, BC goes from ~.659 to ~.658
It's a mix, so BC might change anywhere from .001 to .002(or about 1% max)
At 1kyd the drop difference from 3kfpsMV & .002BC amounts to .3"
(thats .028moa)
I am sure your BC varies more than this -anyway-
I am also sure that any regular 1kyd shooter is working hard to cut 5 to 6" off their groups. So .3" there is probably not big on their 'things to conquer' list.

I'm not gonna lay out internal ballistics from QL, but a quick check indicates about 2fps increase from a .005 increase in bearing length with the same seating depth. I'd barely see it with 20ft screen spacing on my Oehler. But this would actually make up some of the loss in BC indicated above.
The barrel time change amounts to 1ns (Nanosecond).
If your tune requires this, you hurtin..
And there is always tungsten coating to negate all ballistic traces of this discussion.

Bearing surface checks can't hurt, unless you're doing it in place of things that really matter.
But that is what I believe is happening. I think people skip all the difficulties, condensing them down to bullet weight, or OAL, or bearing length.

Personally, I don't do it even with the best tools. Still working on that 5-6"......
[that's what she said]

You make a pretty good argument, at least for what level of division would be a good idea. The OP said the extreme spread was .015" though not .005. Following your example that would be something around an inch (if the change is linear and not somehow exponential?) at 1000. I guess everyone can decide for themselves if that matters in their application.

For myself, I do it because it is easy, does not cost anything, and I am already doing nearly everything else I can reasonably do to improve my reloads so why not?
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