107 pointed SMK BTO

[Mulligan]

Just opened a box of the factory pointed 107 Sierra Match Kings.
I measured BTO on them, the results;
12 measured .5305
75 measured .531
13 measured .532

I measured all of them twice just to be positive..

Question 1.) is it really worth the time to measure the other 1900?

Question 2.) does .001 BTO make a difference at 1000 yards?

Question 3.) is this kind of consistency normal?

I started shooting F-class a few months ago, pertty new to this.
Mulligan

 

[mikecr]

You went through the trouble to measure it, and I sincerely wonder Why.
So,, what does base to ogive variance mean to you?
Do you think it affects BC, in a specific way?
Muzzle velocity? Stability?

 

[Mulligan]

You went through the trouble to measure it, and I sincerely wonder Why.
So,, what does base to ogive variance mean to you?
Do you think it affects BC, in a specific way?
Muzzle velocity? Stability?

When we ( my son and his friends) shot high power we sorted all of our bullets in groups with about .003 difference BTO.
Our groups on target shrunk fairly dramatically at 600!yards after sorting.

 

[Cakes]

The guy is new. Why answer a question with a question??? Eric in DL

 

[shoot4fun]

I sort all my Berger's. I do it for two reasons; first one is I trim meplats and point them so sorting results in more consistency post-process and, second, there are always a few in a 500 box that are well out of range of the rest. Maybe one or two thousandths isn't enough to matter but that one that's way off will leave you scratching your head at the next match.

 

[billlarson]

I sort all my Berger's. I do it for two reasons; first one is I trim meplats and point them so sorting results in more consistency post-process and, second, there are always a few in a 500 box that are well out of range of the rest. Maybe one or two thousandths isn't enough to matter but that one that's way off will leave you scratching your head at the next match.

+2 AMAN........ I would use the 13 for siters..... and keep the others at opp. ends of range box....
bill

 

[Laurie]

You went through the trouble to measure it, and I sincerely wonder Why.
So,, what does base to ogive variance mean to you?
Do you think it affects BC, in a specific way?
Muzzle velocity? Stability?

Well ... it certainly does something! Loading 6.8SPC with el cheapo Remington 115gn FMJBTs, COALs were all over the place as were groups. A BTO check showed vast differences and a bit of batching saw consistent COALs and 3-4 inch 100 yard groups more than halved to around 1.5-inches. Not that I would normally bother with bullets like this, but these were so poor that they might as well be put straight into in the scrap metal skip at the local recycling centre as using them out of the plastic baggie was just a waste or powder, primer, and barrel life.

Yes, that's an extreme example, but the principle generally applies. I find that loaded round comparator OALs reduce using batched match bullets compared to results with unsorted examples in a typical out of the box 3 to 4 thou' range, and to me this is about getting another little bit of consistency - ie the amount of jump that the part of the bullet that is somewhere around lands diameter takes to hit those lands after ignition is the same for every round, or if seated into the lands is by the same amount to a single thou' for every round.

I've twice seen significant measurable improvements through this, thne first being 90gn VLDs in a super-freebore 223 Rem chamber which reduced ES/SD significantly, and secondly in some Sierra 7mm 180gn MKs that I got in bulk 1,000s at a silly price as the initial recipient gave up on them. BTO batching, trimming and pointing have transformed 1,000 yard 'elevations' from poor to as good as I can get with Berger VLDs.

With a range of one and a half thou', I doubt if I'd bother batching, but would likely still do a quick check on every bullet to weed out any occasional 'rogue' example. By coincidence, I also use 107gn SMKs, but these are the last of a large lot of 15-20 year old ones in the old Sierra cardboard 100-ct cartons, and they do need batching. Sierra has improved enormously in recent years.

 

[mikecr]

Well ... My questions have not been answered, and OP's questions have not been answered either.
I'm left to summarize the responses to 'it does something', and nothing specific,, which is meaningless.
These anecdotes go all over, loosely covering many abstracts, but not specific attributes of BTO.
Right?
'Base to Ogive' thats:
- Ogive datum, as affected by ogive radius
+ Bearing length, and not diameter
+ Base length, and not base angle, or end diameter

BTO = OGIVE DATUM + BEARING LENGTH + BASE LENGTH

Now, each of these are different, but not separated in BTO measure. So it seems to me that significance in BTO results is still a ways from being determined here. For example, you couldn't suggest that .003 of BTO departure means Higher ES, as your ogive datum stands unqualified, and ~.0025 of it could be in base length. It might all be in ogive datum variance. Neither affecting MV.
If one of the 3 attributes lowers BC, another could raise it as much. On seating, this is entirely about ogive radius, which is not determined, nor qualified with BTO measure. It's CBTO, as determined in seating testing, and as should be verified(every time) in reloading.
If meplat trimming from bullet base, this is purely OAL, and not BTO.
If meplat trimming from an ogive datum, again, this is not in BTO.

So if convinced that BTO 'does something' then I would think you would want to actually know what that 'something' is.
This is the nature of my stacked questioning. I'm seeking qualified, logical reasoning.
With this, either I, or someone here, could possibly answer OP's question. Until then, nobody can, as other answers are not credible.

 

[Laurie]

Right then nobody knows, and results from others are incredible. Fair enough, that's your view and your choice, and it's obviously a waste of time to say anything to you. Like everybody else, go out and do your thing, or in this case apparently nothing. I'm all for (other) competitors doing nothing ... the ones I worry about are those who do lots of things, find out what works for them, and then put in continuously improving scores as a result.

Just for the record though, I used to measure bearing surface length too, but stopped after Bryan Litz said on these forums it was wasted effort and BTO checking is all that's needed. I've never seen any reason since to regret keeping it simple.

.... and I understand perfectly well that bullet trimming affects OAL alone, but the reason I do it with these SMKs is that they have 1) very 'messy', uneven, and inconsistent meplats, and 2) because a common bullet length gives a more consistent result in pointing.

 

[billlarson]

The guy is new. Why answer a question with a question??? Eric in DL

+2............
mikecr, instead of rudely answering the mans question........("You went through the trouble to measure it" )....... like you know the answer to it.......
then asking your own questions hijacking his thread.....why not take the time to ask your own questions... in your own thread......????
bill larson

 

[dmoran]

Why I qualify bullets by "base to ogive" is: to measure for variation to near a point on the bullet where it will engage the rifling. Variation to that point will directly effect my seating "touch" number. Then when qualified to that point, all further measurements/qualifications forward have relevance from my "touch" as well, and to aid in pin-pointing where any further variation are. Such as near seater-stem diameter.
Donovan

 

[mikecr]

I'm trying to help. Notice there are no real answers to OP's questions..
It's nothing to be emotional about. Just basic reasoning.
Reloading is not like driving a car at night, swerving around the unknown for survival.
With reloading you have plenty of time to think about what you're doing, and act on your best rational understanding.
Without understanding, and knowing this, should you act? How do you know what action to take?

Have you considered that some of these bullets separated by BTO might actually equal the best bullets in the box?
All the bullets are unique in some regard. They hold their character. So it's logical to choose some aspect of that character that matters, and match them to this. For 1kyd shooting, I think, this is me, that matching BC matters most. I think there is nothing out of BTO that will affect MV, but could affect BC. So if I were to match anything about bullets, it would be BC. The biggest bang for the buck there is meplats, and qualified ogive radius is vital to the best in meplat work.
Your BTO culled bullets could match in BC. Your BTO matched bullets could be all over the map for BC.
If you agree, you can run the numbers, then you might understand that efforts in BTO can actually be counterproductive to this end.

dmoran, BTO does not qualify ogive radius.
BTO = AN OGIVE DATUM + BEARING LENGTH + BASE LENGTH
The only way to qualify ogive datum to that of land touching is to calculate that datum and then set it so with your tool(like with a blade mic).
Then, this datum is nearly all rearward on the ogive and meaningless to anything ahead of it (like for seater stem contact point).
BTO helps nothing w/resp to ogive radius (which affects all ogive datums at once).
The only marketed tool for qualifying ogive radius, is a Bob Green Comparator.

 

[dmoran]

mikecr -
Skip the rest of the bullet and just focus on base to ogive. Ones longer in length will have more bullet in the case, and vise-versa for shorter ones.
There for if qualified with a Bob Green only, any un-measured variation before his tool, will reflect in variations to how much of the bullet is seated into the case and to "touch". Which in all my experience and testing proves relevance, and is directly effecting load density, which effects pressure/velocity (hence accuracy and vertical dispersion) besides possible friction variance effects.
Donovan

 

[normmatzen]

DMORAN,

RIGHT ON!