Sorting Bullets by BTO, what are we really doing?

[mikecr]

Ok I’ll ask a dumb question. Has there ever been a seating stem developed that touches the bullet on the ojive instead of up further closer to the tip?

It wouldn't work.
The interference angle is too shallow and so the stem would wedge a great deal, creating huge seating variances.
Seating stems make contact right where they need to.

 

[Mulligan]

Ok I’ll ask a dumb question. Has there ever been a seating stem developed that touches the bullet on the ojive instead of up further closer to the tip?

The seating die made by Century 21 appears to contact the bullet a good bit closer to the case mouth, how close it really is, I do not know.
CW

http://www.xxicsi.com/calibrated-bullet-seater.html

 

[Ccrider]

I would think that is too much.
I have about 12,000 J-4 and around 4500 Sierra 6mm jackets on hand. They are out f the same lot, or run. I can check the lengths of the new jackets, and they are all within .003 inch in length.
So, assuming they are using jackets similar to these, what is causing the bullets to have a different OAL when finished.

I am not sure what is causing the difference. As Bart alluded to, part of it is in the way they are pointed.

 

[mikecr]

Just look at a bullet & where seating forces need to push on it.
No matter what you do with a seater plug, the actual pushing will occur at the smallest diameter contact point. To be successful at all, this will be within 1/3 of nose length from meplat.

 

[Dusty Stevens]

Ok I’ll ask a dumb question. Has there ever been a seating stem developed that touches the bullet on the ojive instead of up further closer to the tip?

Yes and it works very good. The closer you push to where it contacts the barrel lands the more consistent the seating depth that matters. Just buy good bullets and worry about other things that matter. If it turns out your bullet sorting is what is holding you back you just need better bullets.

 

[johara1]

I will say this about the A-Tips and a magnum case, don’t sort them out. They will sort you out differently when the match is over, provided there’s wind. I saw for myself in a LR multi-day match, switching over to them at the end. In the true absence of wind, which can never be counted on going in to a match, I don’t think any bullet in a box of the current match bullets will actually cost a nine, though. At least we haven’t seen it shooting the extremes versus sorted at 600, locally. I’ve seen $.30 bullets shoot over 20x’s at 600.

Add challenging winds, and the theory is that the same shooter will score higher in correlation to the difference in BC with equally uniform bullets, whether they be the same or different. Clearest example being that a box of identical Berger 200-20X’s would shoot different scores in severe wind between a tuned magnum Open and tuned TR rifle with the same shooter, all other things equal. (.308 trajectory being a magnum’s without the first bit of the curve).

Consensus is that bullet to bullet uniformity has a smaller effect on score at close range than long range. I would wonder if uniformity also has a smaller effect on the score values of faster, versus the slower moving of two identical bullets. Perhaps minute differences in BC would have a smaller lateral effect but a greater vertical effect, the faster a bullet goes, as aerodynamic resistance curves for an object transition from predominantly forward to upward more steeply (nonlinear), as speed increases.

First you are making reference to F class, Short range uniformity is not as critical at it is at long range. Br is more critical than F class, that is why you can't measure groups on an electronic target, they aren't that accurate.
Two totally different games accuracy levels are also different..... jim

 

[Rope2horns]

First you are making reference to F class, Short range uniformity is not as critical at it is at long range. Br is more critical than F class, that is why you can't measure groups on an electronic target, they aren't that accurate.
Two totally different games accuracy levels are also different..... jim

Guys are laying down 17,18,19 x's at 1k in Fopen fairly often.....that's a lot of shots inside a 5" circle on pulled targets not electronic. I would think some of those rifles would be competitive if not capable of winning at LR BR?

 

[Mulligan]

Guys are laying down 17,18,19 x's at 1k in Fopen fairly often.....that's a lot of shots inside a 5" circle on pulled targets not electronic. I would think some of those rifles would be competitive if not capable of winning at LR BR?

Norm,
you are correct.
David Gosnell shows us how it's done on a regular basis at our 600 yard IBS matches. He has many times won HG Group with his 284 F-Open rig.
CW

@Zilla

 

[johara1]

Guys are laying down 17,18,19 x's at 1k in Fopen fairly often.....that's a lot of shots inside a 5" circle on pulled targets not electronic. I would think some of those rifles would be competitive if not capable of winning at LR BR?

First you are too heavy for LG. So you have to go in HG. Give it a try you maybe able to be competitive Go look at the records in Heavy Gun it would give you a better idea. Best go to a match and give it a try...... jim

 

[INTJ]

Ok I’ll ask a dumb question. Has there ever been a seating stem developed that touches the bullet on the ojive instead of up further closer to the tip?

A fellow LR BR shooter, who also shoots SR BR, has developed several tools that many top competitors use.

He makes a comparator that measures the bullet where the seater stem contacts it (seater ogive or SO), and another comparator that measures where the bullet contacts the chamber (chamber ogive or CO). These two places on the bullet are not usually where a typical ogive tool contacts the bullet. He also make a comparator for a caliper that matches the seater stem (SO) tool.

When bullets are sorted by SO and CO, they all seat the same and all have the same distance from the chamber. He also has made an machine (Bullet Genie) that spins bullets and allows them to be sorted into batches that will group together.

This concept has been validated by blind testing in a 200 yd shooting tunnel. Also, when measuring unsorted bullets that have been seated the same with standard ogive tools, you can see that the bullets are not seated as consistently as you thought.

So does this matter on paper at 600 and 1000 yds? It depends.

1. If you are talking unsorted Berger bullets seated at the lands, it will likely make a difference. Berger's are very inconsistent, but when sorted by SO and CO and then spun on the Genie, they are shoot as well as any custom bullet.

2. If your Berger's are BTO sorted and jumping .015 or more, SO/CO sorting doesn't help as much. Sorting with the Bullet Genie will help if you are shooting in very good conditions. In poor conditions it probably won't matter much.

3. If you are using good custom bullets like @BartsBullets makes (and others), then SO/CO sorting doesn't help as much. The Genie doesn't help as much either unless conditions are very good.

4. If you are not shooting to BR standards, or you are using custom bullets well off the lands (or jammed well in), or are shooting in poor conditions, then much of this sorting won't make much of a difference. In average conditions it will help a little, and in a competition, even a little help is a big plus.

With all that in mind, for LR BR, I sort all the bullets by SO/CO and spin them in the Genie regardless of the brand. This makes sure I have done everything possible to have consistent bullets. For hunting rifles I only sort BTO--that helps find any bullets that are significantly different than the others. This seems to be the best perceive for what I have seen on paper so far.

 

[mikecr]

Your 'SO/CO' is available as a Bob Green Comparator (BGC)($250). https://greensrifles.com/new-product-page
It's a good tool that functions* to compare ogive radius.
With matched ogive radius from your bullets, you have qualified nose datums.
That's all, it means nothing else.

But this is an important prerequisite to the BTO measure in discussion here.
Where your ogive radius departs from others, your BTO datum changes, and then you could think there is a BTO departure where there might not be at all. You could just as well miss a departure if the ogive counters.
Measuring off angles is never straight forward..

*Disregard the merchandising behind it, as it is seriously flawed. The comparison by itself DOES NOT indicate a problem.

 

[INTJ]

Your 'SO/CO' is available as a Bob Green Comparator (BGC)($250). https://greensrifles.com/new-product-page
It's a good tool that functions* to compare ogive radius.
With matched ogive radius from your bullets, you have qualified nose datums.
That's all, it means nothing else.

But this is an important prerequisite to the BTO measure in discussion here.
Where your ogive radius departs from others, your BTO datum changes, and then you could think there is a BTO departure where there might not be at all. You could just as well miss a departure if the ogive counters.
Measuring off angles is never straight forward..

*Disregard the merchandising behind it, as it is seriously flawed. The comparison by itself DOES NOT indicate a problem.

I don't know if Bob's tool measure exactly what the SO/CO tools measure. The SO/CO maker is extremely busy and doesn't have a lot of time to make them so he doesn't advertise them. The collimators he makes could be made by anyone with a lathe, and I expect to have to make my own from now on. There is one collimator for SO, one for CO, and a comparator insert that matches the CO collimator.

What I do know is the SO/CO process allows bullets that will seat the same to be sorted together. Measuring the ogive with standard ogive tools does NOT always give you a consistent distance between the bullet and where it contacts the rifling. When we are jumping say .015" or more is doesn't matter much. If we are close to the lands it does.

Finally, all this has been tested by Lou Murdica in his tunnel.

 

[mikecr]

There are advanced ways to do it, and simple but time consuming ways.
The BGC takes a meplat trimmer tool piece and machines the back end to accept an indicator stem in place of it's end mill. A modified Wilson(I believe) seater stem is attached to that indicator, which is now within the trimmer tool. So a bullet nose is inserted to stop against a point near bearing, and at the same time a seater stem is against it's normal datum.
It's not a measure, but a comparison, so the dial indicator is zero'd on a standard bullet and all others show deviation from this.

 

[Laguna Freak]

I can only speak from my own experience. IME seating depth accuracy nodes are generally only a few thousandths wide at most. Many bullets in a lot will vary BTO by a couple or few thousandths. Thus, when seating it is quite helpful to have bullets sorted by BTO so all completed rounds in a loading session result in CBTO that is within that rifle : bullet identified seating depth accuracy node.

Real world examples:

Steyr 30-06 that shoots 150 Accubond @2911 fps to 0.3 moa at 100 and 0.4+ moa at 300 + when seated .070 to .075 off lands.

Win M70 300 WSM that shoots 180 Scirocco II @ 2920 fps to 0.4 moa at 100 when seated .058 to .060 off lands. (This is a mid-range charge weight and load development is ongoing with this bullet : rifle combo)


In both cases the groups open dramatically outside the identified seating depth accuracy node.

 

[Bc'z]

I can only speak from my own experience. IME seating depth accuracy nodes are generally only a few thousandths wide at most. Many bullets in a lot will vary BTO by a couple or few thousandths. Thus, when seating it is quite helpful to have bullets sorted by BTO so all completed rounds in a loading session result in CBTO that is within that rifle : bullet identified seating depth accuracy node.

Real world examples:

Steyr 30-06 that shoots 150 Accubond @2911 fps to 0.3 moa at 100 and 0.4+ moa at 300 + when seated .070 to .075 off lands.

Win M70 300 WSM that shoots 180 Scirocco II @ 2920 fps to 0.4 moa at 100 when seated .058 to .060 off lands. (This is a mid-range charge weight and load development is ongoing with this bullet : rifle combo)


In both cases the groups open dramatically outside the identified seating depth accuracy node.

True to a point, let's look a little closer.
I do my seating tests in .003 increments.
Never have I followed Berger's guidance of large jumps.
After finding jam/ touch I'll start development @ .010-.015 off, I never move closer to the lands. I'll pose question this later.
Say I'm getting .75"@100 initially, then seating my .003 increments I notice .018 is .5"@100, .021 is .3" @100, .024 is .1 @100
But notice groups opening up at .027.
This give me a window of accuracy on target of .5 moa over .009" of seating depth if loaded on front side of .024 off the lands.
Knowing barrels are going to erode, some faster than others, staying on top of seating node is more critical than .001 in bullet variation.

Jamming bullets..
This is a honest question for you jammers,as I constantly read about jamming bullets x amount into the lands with lighter neck tension.
How can you be for certain that your .006 jam is truly what you think it is?
Wouldn't the lands work as a seating die and seat bullet deeper into the case as bolt closes?
This I gotta know.

 

[Mulligan]

True to a point, let's look a little closer.
I do my seating tests in .003 increments.
Never have I followed Berger's guidance of large jumps.
After finding jam/ touch I'll start development @ .010-.015 off, I never move closer to the lands. I'll pose question this later.
Say I'm getting .75"@100 initially, then seating my .003 increments I notice .018 is .5"@100, .021 is .3" @100, .024 is .1 @100
But notice groups opening up at .027.
This give me a window of accuracy on target of .5 moa over .009" of seating depth if loaded on front side of .024 off the lands.
Knowing barrels are going to erode, some faster than others, staying on top of seating node is more critical than .001 in bullet variation.

Jamming bullets..
This is a honest question for you jammers,as I constantly read about jamming bullets x amount into the lands with lighter neck tension.
How can you be for certain that your .006 jam is truly what you think it is?
Wouldn't the lands work as a seating die and seat bullet deeper into the case as bolt closes?
This I gotta know.

If you are "soft seating", they yes. When you close the bolt you are seating the bullet the "rest of the way". I know several shooters that do this and are successful with it.

If you use a little more neck tension, then within reason, you are just jamming a bit more.

I Jam my bullets, on the rifle my daughter shoots in IBS long range (6 dasher) we have determined the rifle wants .004 jam. Every time we load we stay on top of the seating depth....... it is a lot of work sorting and measuring but it works.
CW

 

[newbieshooter]

.....

Jamming bullets..
This is a honest question for you jammers,as I constantly read about jamming bullets x amount into the lands with lighter neck tension.
How can you be for certain that your .006 jam is truly what you think it is?
Wouldn't the lands work as a seating die and seat bullet deeper into the case as bolt closes?
This I gotta know.

Did it jam or not?? | Shooters' Forum (accurateshooter.com)

 

[mikecr]

BTO is not going to predict accurate CBTO. That just has to be measured to know,, every single round.
Now if these measurements leave you fighting to nail desired CBTO, then you should consider an ogive comparator(a ~BGC as mentioned) to qualify nose shapes before seating.
But you still have to measure each CBTO to know it.

BTO itself means nothing until you determine the source of deviation within it's base length + bearing length + ogive datum. You should consider this truth & not go beyond until you understand this measure.

 

[Straightshooter1]

When I'm surfing, I try to avoid eddies. But I'm really drawn to this one regarding BTO and BS (Bearing Surface).

I only precision reload for my .308 and primarily use Bergers and SMK's and though I do no competitive shooting, I endeavor to load the best possible cartridges I can to best measure what skill I might have as a marksman. To that end, being schooled with some science and physics, AND being a bit of a perfectionist. . . I'll measure everything and take notes to best understand what to do to get the most consistent cartridges (when one is retires, it's a lot easier to do ).

So, about 3 years back I got a batch of SMK's that have a large difference in BTO's and also in their BSL's. So, I sorted them by BSL (Bearing Surface Length) and selected 20 from each end of the spread to fire and record the results. There was a .034 difference in the BSL's and I wanted to see what kind of difference it makes (if anything). Though my reloading equipment wasn't as good as it is now to give me good consistency for record, the data and what showed on paper did stand out as a significant difference.

Some of the things I saw in my measurements were:
*A strong correlation between BSL and seating depth
*A correlation between BSL and BTO where the difference was close to the same
*A correlation between BSL and the bullet's OAL
*No noticeable correlation to the bullet's weight

Also, I noted a noticeable POI shift between the two sets of 20 bullets.

See pics below.

For a time, I'd sort by BSL, but when I looked at the variance between BTO's and BSL's, it was so little that I just sorted by BTO (if I find difference's in the lot/batch greater than .003). Now though, I don't use a comparator with the diameter of the ogive to sort, but use a comparator with the diameter of my seating stem. Whenever I sort now, this gives me very consistent CBTO measurements (that's right, not the same tool used for sorting).

 

[Laguna Freak]

Say I'm getting .75"@100 initially, then seating my .003 increments I notice .018 is .5"@100, .021 is .3" @100, .024 is .1 @100
But notice groups opening up at .027.
This give me a window of accuracy on target of .5 moa over .009" of seating depth if loaded on front side of .024 off the lands.

It seems like you are using the method Erik Cortina promotes. No doubt a very good method.

When I tried it, I got POI’s that were significantly different as I worked that method from say a 0.068 jump to a 0.078 jump even though the 3 or more shots at each jump distance grouped reasonably or sub-moa. As a result I took it one step further by doing a modified ladder type test where I would shoot the most promising seating depths, eg; 1 shot each from say 0.068 to 0.078 at 0.001 increments to identify which cbto lengths grouped closest together. My emphasis is on very low vertical spread as long as the horizontal spread was moa or smaller and not more than 50% greater than the vertical spread. I have developed confidence that this method precisely identifies the full width of a seating depth accuracy node. I will not accept a node that is less than 0.003 wide because it is too narrow to be of substantive benefit in my opinion.