Bullet Base to Ogive Grouping

[Straightshooter1]

The point of the exercise is the bullets get seated by the stem on your bullet seater. It contacts the exact same dimension on the nose of each of the bullets. So even though there are variations in the base to ogive measurement among your bullets, the Bullet stem places the bullets to the same spot. Which is why measuring bullets base to ogive is a waste of time.

Bart

I agree about measuring bullets BTO's as any difference in jump is NOT a issue for me since I don't load my cartridges to touch or jam the lands. But I do sort my bullets from the base to the point where my seater stem makes contact with the bullet. Since consistent seating depth is a big deal, I want my bullets seated to the same depth in every case case. Sorting this way works really well and it give me very consistent cartridges even though the CBTO can vary.

I know this topic has been discussed many times and I have read most of the threads regarding it, but I haven't seen much regarding how people actually group their bullets. I just measured 200 Berger 105gr Hybrids all from the same lot, using a Hornaday comparator mounted on a Mitutoyo "Absolute" caliper. Here is what I found:

View attachment 1290476

What I am looking for is a better understanding of how fine/course to group these. I am really considering just throwing them all together, since 99.5% fall within .004 and 86.5% fall within .002. Frankly, I doubt I can shoot the difference here. My discipline is primarily 600 yd. F-class.

Any thoughts would be appreciated.

I will sort my bullets by the method above in groups +/- .001. Like you've shown, it not unusual to have outliers, which I will use for fouling the barrel after a good cleaning or set them aside to be used for fire forming.

 

[PRR1957]

The only dimensional difference should be in the bullets bearing surface length. Ogive in relation to head space should be unaffected.

 

[dstoenner]

Correct me if I'm wrong, but how does BBTO effect jump? The die references off some point on the ogive and seats the bullets consistently from that point. The distance from that point to the bullet base has nothing to do with jump.

You are measuring at about the point the bullet would contact the lands. But the bullet is seated by a point much further up the nose. The base isn’t even referenced to where the COAL is going to happen. Therefore the ogive point is going to fluctuate up and down resulting in a seating error relative to your target seat.

 

[RegionRat]

When I was young and curious about these things, I would save up the ones on the two ends of the tails and the flyers and when I had enough of them, I would test.

 

[darkangel_r2]

I sort by bearing surface. Always use the same comparator on the same side of the bullet.

Bullet Sorting Experiment - Part One - Ammolytics

A detailed experiment to measure the actual effects of bullet sorting by weight and length for precision rifles.

blog.ammolytics.com

 

[BartsBullets]

My guess is you may find the egregious outlier from time to time.

At 600 yards, does it really matter?

At 1000 yards BC would be the greatest concern. Would that be measured by bullet OAL? Ogive is irrelevant at that point in the BC calculation?

Just curious. I was thinking about getting into bullet sorting, but do I really need to do another step...

When I sort bullets it’s ONLY by overall length. Because of BC.

 

[JMayo]

I set up my seating depth, best i can get it. Then sort by OAlength, row them up
Put em in the box as they stand, keeping the shortest from the longest.
Does it do chit ? I believe it does. Belief is a strong emotion.
My toys, my beliefs ...MY Way !
See ya at the range !

 

[JFrank]

I know guys that sort each bullet many ways.

Base to ogive
Bearing surface
Base to seater stem
Base to chamber ( dont ask me how)
OAL
Weight
Spin
X ray

 

[RGRobinett]

The point of the exercise is the bullets get seated by the stem on your bullet seater. It contacts the exact same dimension on the nose of each of the bullets. So even though there are variations in the base to ogive measurement among your bullets, the Bullet stem places the bullets to the same spot. Which is why measuring bullets base to ogive is a waste of time.

Bart

Presuming that all of the bullets were pointed using the same die, Bart has nailed the B:O question.
Following his outline, if bolt-face/case-head to ogive measurement varies, THAT would imply a 'mixed Lot': bullets from different point (nose-form) dies.
Bart also identified (#26) that, so long as bullets are formed in the same die, the only attribute, worth measuring, is OAL, which affects BC . . . RG

 

[BartsBullets]

I know guys that sort each bullet many ways.

Base to ogive
Bearing surface
Base to seater stem
Base to chamber ( dont ask me how)
OAL
Weight
Spin
X ray

Good news is they aren’t hurting anything.

Bart

 

[Ned Ludd]

A seating die stem contacts the ogive well out toward the meplat of the bullet. A caliper insert contacts the ogive slightly above the bearing surface close to where the bullet will first contact the lands. The bullet boattail and bearing surface are both well below these two points. Thus, sorting bullets by BTO dimensions is generally going to have little, if any, effect on seating depth as measured using calipers. In other words, the entire BTO dimension is outside the two critical contact points; i.e. the point near the meplat at which the seating die stem contacts and pushes the bullet down into the case neck during seating, and the point just above the top of the bearing surface where we actually measure CBTO (i.e. effectively, seating depth). Sorting bullets using the BTO dimension, which lies completely outside these two critical points is not going to affect seating depth.

What variance in bullet BTO can affect are the length of bullet bearing surface inside/contacting the case neck wall, and the effective/usable case volume. The first of these would relate to possible frictional differences between the bullet bearing surface and the case neck wall for bullets with different BTO dimensions, the second would relate to possible changes in pressure for a given load. The real question is whether the difference between either of these two variables would be large enough for bullets that vary in BTO dimension by only a few thousandths that it would make a significant difference on the target. Of course, that can only be decided by the individual after rigorous testing.

But consider what we are actually doing when we carry out a seating depth test. Effectively, a seating depth test is also moving the bullet boattail/bearing surface in/out of the neck, thereby potentially changing both the amount of bearing surface contacting the case neck wall, as well as the effective case volume. With regard to both friction between the bullet bearing surface/neck wall and the relative change in effective case volume, how much change in velocity/pressure does one typically observe during seating depth testing? The answer largely depends on the total test range over which the bullets are seated. Seating a jumped bullet .050" or further off the lands can noticeably increase pressure; changing the seating depth of a jumped bullet by only .010" or .020", not so much. If I cannot detect a significant change in velocity/pressure across a typical seating depth test with bullets seated from about .003" off the lands, to about .024" - .027" off the lands (essentially all of the bullets I shoot will tune in somewhere within this range), then as an F-TR shooter I am going to be relatively unconcerned about BTO variance of a few thousandths. For that reason, I also sort bullets by OAL only. Nonetheless, for shooting disciplines where the ultimate precision of a load is everything (i.e. BR), the effect of BTO length variance is a testable commodity. If you think it might make a difference, the easiest approach initially is to load a few bullets from the two BTO extremes (i.e. longest/shortest) and see if you can shoot the difference in terms of precision, or detect any difference in velocity/pressure. Then you will know whether sorting bullets by BTO will have a significant effect on precision in your hands.

 

[darkangel_r2]

When I sort bullets it’s ONLY by overall length. Because of BC.

Do you know which dimension varies the most? Nose, bearing surface, boat tail length? Are some dimensions more consistent than others due to the way bullets are made?

 

[BartsBullets]

Do you know which dimension varies the most? Nose, bearing surface, boat tail length? Are some dimensions more consistent than others due to the way bullets are made?

Bearing surface with custom bullets Varys very little and as I stated earlier doesn’t really matter when reloading. Boattail is the same.

Overall length varies because of the way the bullets forms to make the meplat. Typically the longer the bullet the smaller the meplat (equals slightly higher BC) the shorter the Bullet the bigger the meplat (lower BC).

 

[mikecr]

Good news is they aren’t hurting anything.

If they don't understand what they're doing, and acting on it, it's likely they're making things worse.

 

[mikecr]

Overall length varies because of the way the bullets forms to make the meplat. Typically the longer the bullet the smaller the meplat (equals slightly higher BC) the shorter the Bullet the bigger the meplat (lower BC).

Unless ogive radius varies,, which they do.

 

[BartsBullets]

Unless ogive radius varies,, which they do.

No they don’t. Not bullets made from the same point die.

 

[Lefty Trigger]

The only sorting I do is the color of the box they come in. I'm not good enough to try any other type of sorting, it just make my head hurt...

 

[wkdickinson]

No they don’t. Not bullets made from the same point die.

I think that is the key - we all assume that bullets from the same "lot" were made on the same die and that is obviously not the case. I don't really want to target Berger, but because the population we are considering was made by Berger, I guess we have no choice. Like all large scale product manufacturing companies, they likely have a "tolerance" of X +/- from the target length, BTO, wt, etc. Apparently that tolerance is/can be pretty wide.

 

[Bill Norris]

Only bullet measuring I do is bearing surface when trying a new unknown load. And only for comparison with other known loads.

 

[BartsBullets]

I think that is the key - we all assume that bullets from the same "lot" were made on the same die and that is obviously not the case. I don't really want to target Berger, but because the population we are considering was made by Berger, I guess we have no choice. Like all large scale product manufacturing companies, they likely have a "tolerance" of X +/- from the target length, BTO, wt, etc. Apparently that tolerance is/can be pretty wide.

Since I’m a custom bullet maker it’s not in my thought process of bullets coming out of a different die. But if guys are buying machine made bullets it’s a possibility.

Bart