BBTO or bearing surface?

[ckaberna]

Where is the most “bang” for your time sorting by bullet base to o-give or bearing surface for BR accuracy?
I have sorted some Berger 108’s by bearing surface using two hornady comparators but I can still see difference in them when comparing base to ogive.

 

[Dusty Stevens]

Where is the most “bang” for your time sorting by bullet base to o-give or bearing surface for BR accuracy?
I have sorted some Berger 108’s by bearing surface using two hornady comparators but I can still see difference in them when comparing base to ogive.

Gotta sort both ways with those bullets to get the best bang for your buck

 

[JFrank]

Voodoo ""

First OAL
Second weight
Third meplat
Forth BBTO
Fifth bearing surface
Six x ray
Seven color
Eight uhhh oh yeah give um a kiss

OR - load um
You may not be able to shoot the difference.

 

[ckaberna]

Six x ray

LOL .....almost fell out of my chair laughing on this one!

 

[JimSC]

just curious how you are getting bearing surface measurements. I can think of no practical way to determine where the cylinder (bearing surface) ends and the ogive (slope) of a bullet begins

http://mathscinotes.com/2011/01/ballistics-ogives-and-bullet-shapes-part-1/

 

[JFrank]

Pressure ring to ogive if I'm not mistaken

 

[4xforfun]

just curious how you are getting bearing surface measurements. I can think of no practical way to determine where the cylinder (bearing surface) ends and the ogive (slope) of a bullet begins

http://mathscinotes.com/2011/01/ballistics-ogives-and-bullet-shapes-part-1/

That may very well be true, but.... Lets say that you are using two ojive tools...one for the tip and one for the base....like Bill Shehanes system for boat tail bullets...to measure bearing surface length. You may not be in the EXACT spot, but you are very close, and, more importantly, you are in the SAME place with each bullet. You find a bullet(s) that is way long or short, do YOU shoot that bullet with the others....just throw it back in the box?.. Or , do you seperate it...shoot it with other bullets with the same measurement?

Like I said, your point is correct, that exact spot is a tough one, but are you saying to not measure bearing surface?

Tod

 

[ckaberna]

(borrowed pic from net)This is how I am performing it. As stated in pic, it probably will not match bullet manufacturers dimensions but it is repeatable and you can sort by it due to contacting the same reference point on each bullet.

 

[4xforfun]

To the op...I say ojive to ojive.

 

[mikecr]

If you're sorting to match internal ballistics, you should consider testing to determine if bearing makes any difference whatsoever for your bullets/barrel.
If you're sorting to match external ballistics, then you should not dismiss the biggest factors affecting BC. This would put base end and meplat diameter variances way above bearing.

Truly matching bullets would be very difficult, as it would include every single attribute individually -summed mathematically to resolve results. Please invent a practical(<$30K) way to do this!

 

[zipollini]

This is what Bryan Litz has to say about bullet sorting.

 

[4xforfun]

If you're sorting to match internal ballistics, you should consider testing to determine if bearing makes any difference whatsoever for your bullets/barrel.
If you're sorting to match external ballistics, then you should not dismiss the biggest factors affecting BC. This would put base end and meplat diameter variances way above bearing.

Truly matching bullets would be very difficult, as it would include every single attribute individually -summed mathematically to resolve results. Please invent a practical(<$30K) way to do this!

This again may be true....but you don't need a $30K setup to find bullets that DON'T MATCH. If you can find that one or two in every hundred that are "way out", wouldn't that be worth a few bucks?

My thoughts are that any type of measuring WILL NOT make things WORSE.

 

[JFrank]

This is what Bryan Litz has to say about bullet sorting.

BBTO is all I do, although I'm in search of a better tool to accomplish the task over a Hornday comparator.

 

[mikecr]

you don't need a $30K setup to find bullets that DON'T MATCH.

You could identify apparent variances in bearing, for whatever you think that means. I don't think it means anything in itself. BTO means even less.
But, you can't credibly suggest that bullets do or don't match in BC based on a single attribute like this.

To measure all attributes -accurately-, it looks to me that you would need a laser scanning optical comparator/micrometer and custom software. Something like a Keyence IM-7000; https://www.keyence.com/products/measure-sys/image-measure/im/index.jsp

Last time I priced potentials here, I gave up at ~$30K, as buying better bullets was by far the better option.
Another option is to test what you're doing, or think you're doing, and find out if it matters to you. Maybe it doesn't.
That is what I did. I used to measure bearing, BTO, ogive radius, best attempted base angle, end diameter, and meplats. The only difference I could see anywhere with testing was with meplat diameters. This trumped the rest.
So my real bullet improvement is in meplat work, which is great because I don't actually have to try measuring them to improve them.

You could spend a lot of effort trying to accurately measure every attribute of a bullet, and then enter each result into software to calculate it's BC. That's not all that bad, and I do this to determine a baseline BC of my bullet choice. That's grabbing a single bullet out of the box and doing this. No way today I would exhaust this with hundreds of bullets,, yet it would have to be done TO KNOW what actually matches a median in BC for the lot. How do I know this? I tried, and tested, and learned..

 

[dcali]

The nose is the part that varies the most. Meplat diameter and nose length have a meaningful impact on BC, and they’re not unrelated due to the way bullets are formed. Because of that, the way I see it, OAL is probably the most bang for buck if you’re going to sort.

 

[rckendall]

BBTO is all I do, although I'm in search of a better tool to accomplish the task over a Hornday comparator.

This is the tool I use.
https://www.brownells.com/reloading.../sinclair-bullet-sorting-stand-prod38769.aspx

I use a better dial indicator, but the basic tool works well. I put a couple O-rings on the upper portion of the stem of indicator to keep it within "range" if I need to let go of it. I've done a couple thousand now, 500 at a time, and it goes quickly.

Richard

 

[JFrank]

I was looking at those for a couple of purposes, ( headspace comparator included)

 

[Intheshop]

Cast bullet shooter here so please only take this in that light.

I use a Federal Mahr.... "bench",snap gage. Base to where the nose gets engraved by the leade.This is also where the probe goes when checking loaded round,runout. From the center of the nose engaving... to....base. Jacketed bullets are harder to do but still possible.... just mark up the nose real good with ink. Then load several looking,for the leade engraving. Not just a touch point though.... you're looking for a "length" of engraving to show up. In the center of this length is where all data needs to be measured. Then a reamer gets made to cut the matching geometry into the end of the "spud" used in the snap gage. Look at the bullets base as well..... just sayin, it ain't always an ogive issue. Good luck with your project.

 

[Bart B.]

Keep in mind that for cases headspacing on their shoulders, their shoulder is the place bullet touch point at the chamber throat need be referenced to.

Unless all your resized cases have exactly the same headspace.

Case heads are rarely against the bolt face when fired. A thousandth or more head clearance is normal.

 

[mikeeg02]

I think the other Mike has a good point. I've trimmed a few and shot them, pointed a few and shot them, and found a combination of both that helps make them consistent. It's easy to test. And helps allow you to tune out the vertical.

But I sort by bto to point.
Do my trimming / pointing combination
Then sort by bearing surface.

I just did this to 3,500 hybrids over the last couple weeks and unfortunately I havent found the correlation that Bryan litz is referring to in that video between bearing surface and bto. I think to properly sort you need to do both. Were not fighting for inches at 1k anymore. Were down to ten thousandths.

Really you need to test it all. I wish I knew at the beginning of this season what I learned over the season. I'm sure everyone says that every year.