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Sorting Bullets by BTO, what are we really doing?

Texas10

There arose a while back a discussion on sorting bullets not by weight, but by BTO or base to ogive. Experts agreed that this method was more beneficial to shooting smaller groups than sorting by weight, but for the life of me I could not understand how moving a seating depth by .001 or .002 could or would cause a measurable change in groups size, nor for that matter how a bullet that was a few tenths of a grain different in weight would have a negative effect on groups.

So my question to those bonafide experts here is this, what are you really accomplishing by sorting bullets either by weight or BTO? What factor makes say two bullets shoot identically, and yet a third land somewhere out in the boondocks?

Not being one to ask a question without first having thought about the answer, I began by researching how jacketed bullet are manufactured, and how small changes in bullet weight or profile might make a difference big enough to warrant the extra work.

This is where a guy who actually makes his own bullets will hopefully chime in with some real world experience.

I will save my take on this until after others more experienced have given their opinion. Hopefully a vibrant and informative discussion will follow. I yearn for an answer that's more complex than say, "every top finisher sorts bullets".

Merry Christmas and Happy New Year to all.
 
Uniformity can only help not hurt. Since it is not required anyone with doubts needs not participate. I have never found gain by sorting cases by weight, so I no longer do it. There is nothing in the steps we do that equal the correlation between accessing the conditions and making the shot properly.
 
Texas10 said:
There arose a while back a discussion on sorting bullets not by weight, but by BTO or base to ogive. Experts agreed that this method was more beneficial to shooting smaller groups than sorting by weight, but for the life of me I could not understand how moving a seating depth by .001 or .002 could or would cause a measurable change in groups size, nor for that matter how a bullet that was a few tenths of a grain different in weight would have a negative effect on groups.

So my question to those bonafide experts here is this, what are you really accomplishing by sorting bullets either by weight or BTO? What factor makes say two bullets shoot identically, and yet a third land somewhere out in the boondocks?

Not being one to ask a question without first having thought about the answer, I began by researching how jacketed bullet are manufactured, and how small changes in bullet weight or profile might make a difference big enough to warrant the extra work.

This is where a guy who actually makes his own bullets will hopefully chime in with some real world experience.

I will save my take on this until after others more experienced have given their opinion. Hopefully a vibrant and informative discussion will follow. I yearn for an answer that's more complex than say, "every top finisher sorts bullets".

Merry Christmas and Happy New Year to all.
Click to expand...
Agree, Mr Litz once said sorting bto was more important than sorting bearing surface???

Bearing surface was the only thing I could see that might have made a major difference besides massive weight fluctuations at distance.
 
First, a difference in base to ogive will not change the seating depth as defined by where the ogive first contacts the lands and grooves, how far into it is or how far away it is. the Seating depth is determined by the ogive’s contact with the seating stem. True, a different amount of the bullet will be inside the case as base to ogive varies, but in the grand scheme of things, this has no bearing on accuracy.
Untill you start shooting true custom bullets, you will get variations in everything from shank diameter, ogive to base measurement, weight, and even the actual profile of the ogive it’s self.

I Make my own 30 caliber bullets for Short Range Score and my own 6mm for Long Range. There Is no way to measure any difference in one bullet to the next this side of a high resolution optical comparator. Semi custom bullets such as Berger, Sierra Match Kings, Hornady ELD Match, etc are a different story. They all vary from lot to lot in various ways.

Extreme accuracy begins with removing variables. That includes bullets that are identical in every respect. Then there is the loading procedure,making reasonably straight and uniform ammunition for the task at hand.

Then there is everything else.
 
The most consistent bullets I have found (I can't roll my own) are the new JLK Bullets from Ed Faber. I have spec'd these out in 6.5 mm for the 130 and 140 grain weights. OAL, weight, BTO, cartridge BTO (which measures the ogive consistency at a different point than the BTO measurement, since the CBTO is set with the seater stem), and another ogive measurement I took to check ogive consistency at 3 different diameters are all the best I've ever seen on production bullets. See my previous posts about these new bullets. And they are very accurate; i.e., they shoot tiny groups.
 
jackieschmidt said:
First, a difference in base to ogive will not change the seating depth as defined by where the ogive first contacts the lands and grooves, how far into it is or how far away it is. the Seating depth is determined by the ogive’s contact with the seating stem. True, a different amount of the bullet will be inside the case as base to ogive varies, but in the grand scheme of things, this has no bearing on accuracy.
Untill you start shooting true custom bullets, you will get variations in everything from shank diameter, ogive to base measurement, weight, and even the actual profile of the ogive it’s self.

I Make my own 30 caliber bullets for Short Range Score and my own 6mm for Long Range. There Is no way to measure any difference in one bullet to the next this side of a high resolution optical comparator. Semi custom bullets such as Berger, Sierra Match Kings, Hornady ELD Match, etc are a different story. They all vary from lot to lot in various ways.

Extreme accuracy begins with removing variables. That includes bullets that are identical in every respect. Then there is the loading procedure,making reasonably straight and uniform ammunition for the task at hand.

Then there is everything else.
Click to expand...
Jackie,

If you have a few minutes to expound on the bullet making, would you briefly hit upon what are the important steps and measurements that make a custom bullet more consistent? I.E. jacket source considerations and why, lead core cutting steps and how small variations in core and cup can make or break a hand made bullet?

So many use the term "keeping everything consistent". We measure this, we measure that , but when do we know that what we're doing is making a difference? Very often in life, just the belief that we're creating something better will often cause us to perform a task better. Increased confidence in one's shooting, for whatever the reason often leads to better results, yes?

And if that's the only reason to sort bullets, than that's good enough. But perhaps there are more concrete reasons to sort by BTO, and I suspect center of gravity is the real reason. What are your thoughts about center of gravity vs center of rotation, wobble, and precession in a cup and core bullet traveling Mach 2+ and spinning at 300,000 rpm?

Inquiring minds would like to know, and will appreciate your time spent sharing a small bit of your expertise.
 
Right or wrong BTO never made any sense to me verses bearing surface. The base of a boatail bullet never touches the barrel, so why would it be even relevant. Not to say one is right or wrong it just doesn't seem logical to me. I'll continue to sort by bearing surface. What I have found over the years is bearing surface sort usually end up with bullets that are the same weight also.
 
As told to me by a benchrest Hall of Famer
I quote
I can stick a 105gr bullet in the same hole as a 103gr, so if you want to sit around playing with yourself, you go right ahead!
Also added
The minimal amount of bearing surface in unsorted bullets is not enough to cause significant changes in preasure.

Occasionally I still play with my tool
I.E. my comparator, but for the most part just pull them from the box.
 
Base to ogive tells you how uniform the bullet maker is making that lot. bearing surface uniformity means a lot at 1000, I hold +- .0005... OAL. is what I look at first, if they are over the place I get rid of them, I had some that varied over .060 in a hand full then I cut some open to see what they look like when they seated the cores last is weigh them. before I wear out a good barrel with them. This is for long range, short range buy good bullet and load them....... jim
 
Bc'z said:
As told to me by a benchrest Hall of Famer
I quote
I can stick a 105gr bullet in the same hole as a 103gr, so if you want to sit around playing with yourself, you go right ahead!
Also added
The minimal amount of bearing surface in unsorted bullets is not enough to cause significant changes in preasure.

Occasionally I still play with my tool
I.E. my comparator, but for the most part just pull them from the box.
Click to expand...
Who compares the comparators ? :rolleyes:
 
I'm a Bench Rest shooter.
Now I make up my bullets by ogive measurements, .."jam or Touching" for example.

Then after all is made I sort by over all length. Put em in the 100 round box in that order.

This was suggested to me by several bullet makers and by established shooters.
My groups were halved @ 600 and my "WTH's" we're not near as big at score.

Did I just get better at it or were the custom bullets that much better or did sorting them do the trick?

A bit of all ....
I think might be the answer.

Having fun with my big boy toys is my goal .... And I sure did last season !
 
jackieschmidt said:
First, a difference in base to ogive will not change the seating depth as defined by where the ogive first contacts the lands and grooves, how far into it is or how far away it is. the Seating depth is determined by the ogive’s contact with the seating stem. True, a different amount of the bullet will be inside the case as base to ogive varies, but in the grand scheme of things, this has no bearing on accuracy.
Click to expand...
As Jackie points out, base-to-ogive differences have no bearing on actual seating depth relative to the lands.





 
I was thinking that what we are sorting out are bullets that can't be expected to fly as predictably as we need to be competitive. Whether sorting by weight, or BTO, or bearing surface, what we may in fact be identifying are bullets that will not fly well due to gyroscopic imbalance because the center of gravity of the lead core will be offset from optimum for the barrel we are shooting it from.

No doubt purchasing top quality bullets whose jackets are very consistent in wall thickness will help keep the center of gravity of the bullet in line with the axis of rotation while spinning at 280,000+ RPM, and this should help keep the bullet better stabilized during its flight.

And a slightly heavier bullet may indicate the center of gravity of the bullet is in a more forward position, giving it better upset resistance in long range situations while approaching subsonic speeds. Or not!

The question that comes to mind is this: Has anyone made any correlation between a lighter bullet within a lot and a further aft (shorter) BTO, or vice versa?

And if so, which one shot more consistently?

Apologies if I'm digging too deep, I have a curious mind that needs constant tickling.

I think what we really need is the Slo Mo guys and a high speed camera setup every 100 yds out to 1000 yds and video the bullet as it passes by.

That wouldn't cost too much, would it?
 
BTO will have an impact on the drag coefficient, thus the BC. Besides the potential impact on aerodynamic jump and bearing length, this is the biggest item I can think of offhand.

So my answer is consistent BC between projectiles.

Just my observation.. sorting is for consistency. Only your process and equipment can determine if the sorting adds value to the results.

As I'm new, this is picking pepper from the fly turds for me.
 
Simple solution, try 5 bto, 5 weighed, 5 oal, 5 bearing surface, and 5 just grabbed. Go to 100yd shoot same seating depth and powder charge. Study target, repeat on different day as close to same conditions as previous. Study both targets, Form your own conclusion about what worked consistently for you....post both targets for everyone to see...don’t use aluminum comparators!!!!!
 
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