Bob Green Comparator and bullet sorting

[lmorrison17]

OK what this tool actually compares is ogive profile variance.
the stem inside the tool is made to match most seater stems, obviously it can't perfectly match every stem from every manufacturer.
The body of the tool is reamed with a lead/throat that i believe is most common for that caliber, once again it cant be a perfect match for ever chamber.

WHat we are looking for is variation, were not measuring anything.

We sort into sublots by ogive profile.

The end result is a consistant seating depth for each sublot.

It has been my experience that a .003-.005 variation in seating depth can be significant and bearing surface variance is not even worth taking the time type the words.

A .040 variation in BS had no affect on my long range loads.

 

[mikecr]

As said, sorting with the BGC get's you to the same ogive radius, and with that your datums match for other measure(like seating), or actions(like meplat trimming). You are 1st qualifying bullet noses.

The BGC opens your eyes to many things,, about what you're actually doing, or not doing,, and it gets you thinking differently.

 

[bozo699]

OK what this tool actually compares is ogive profile variance.
the stem inside the tool is made to match most seater stems, obviously it can't perfectly match every stem from every manufacturer.
The body of the tool is reamed with a lead/throat that i believe is most common for that caliber, once again it cant be a perfect match for ever chamber.

WHat we are looking for is variation, were not measuring anything.

We sort into sublots by ogive profile.

The end result is a consistant seating depth for each sublot.

It has been my experience that a .003-.005 variation in seating depth can be significant and bearing surface variance is not even worth taking the time type the words.

A .040 variation in BS had no affect on my long range loads.

Really?..... Just curious how far are you shooting?... My findings were the opposite of that,..just a beginner trying to learn I guess.
Wayne.

 

[lmorrison17]

600 yds if you'll read back to the beginning of the thread you'll see CigarCop had a similar experience.
These were Berger 6.5 130 vld

 

[johara1]

A variation of .003-4 can completely miss the window…….. I maybe anal but my findings are somewhat closer to a .001 or less is better…. James O'Hara

 

[mikecr]

Wayne, why do you think bearing comparison, which typically includes base length and from unqualified noses, holds any value to us?
What is your logic behind it?

 

[johara1]

One other point, to measure from base to ogive doesn't work…… Bearing surface measurement does, and it does lessen the vertical and ES. I don't use BGC nor do plan to but i made my own from a old BSC and measure the over all loaded round as it would fit in the chamber and it did make a huge improvement…… jim

 

[lmorrison17]

After sorting with a BGC my base to ogive/seating depth stays the same.
I don't measure every round but screen through them pretty thoroughly.
My f-class results speak for themselves.

 

[johara1]

I thought we were talking accuracy not where or what you shoot, Bench rest is all about accuracy being in the middle and small is my only concern, and as you said i will let my results speak for themselves ……. jim

 

[Jay Christopherson]

this forum needs a "whip it out and compare it" emoticon... :

 

[Erik Cortina]

this forum needs a "whip it out and compare it" emoticon... :

Well, get to it Jay! ;D

 

[ZenOhSix]

I just purchased one of these BGC's. I think I have a general grasp of its overall purpose and value. I had a general usage question though, and curious to see how others do it their way.

When sorting into sub-lots, which "lot" do you use as your base for the general seating position? Meaning, if you had sorted through 500 bullets of 168gr SMK (308) and had the following lots:

1) 14 count
2) 400 count
3) 86 count

Assuming that Lot 1 is .001 under Lot 2, and Lot 3 is .001 above Lot 2; it would seem the common intended bullet size was lot 2 by pure count (400). Therefore, when seating your bullets do you use this LOT for your ideal OAL?

If so, here are a few subsequent questions:

1) I have purchased a Hornady Lock n Load OAL Gauge and Comparitor. I was planning on using a bullet from LOT 2 (above question) to check the rifling depth. Just to confirm above, I should use a LOT 2 bullet when gathering this data point?

2) I have purchased a Forster Ultra Micrometer Seater Die. Do I zero the Micrometer to the seating depth that is measured with the Hornady Lock n Load when the bullet is touching the Rifling, or at the backed off values (.020 - ??)? I would think it would make sense to base it off of whatever depth when the bullet touches the rifling; this would then allow me to make easy and accurate seating adjustments for the backed off values?

3) When I am ready to seat a bullet from Lot 3, I would need to back out my die, via the Micrometer, by one thousandth of an inch (as it is .001 longer than LOT 2)? By doing this, would I technically be increasing the OAL of the cartridge by .001?

This is where my mind is having trouble getting around the BGC tool and usage. I am trying to understand this, but I seem to be just going through the "proper" motions. Help?

Thanks,
Mike

 

[Marksman63]

If i can't they are fowlers or sighters

[br]
Not a specific criticism of you, Jim, but I see this frequently and folks should know that homophones are not interchangeable. [br]

Fowl´er
n. 1. A sportsman who pursues wild fowl, or takes or kills for food. [br]
As opposed to "fouler", a firearms-specific term for a shot fired to foul a barrel. Other commonly confused terms are "muzzle break" instead of the correct "muzzle brake" or "rifling lead" instead of "rifling leade".

Thanks! Very good note for non English/American speaking shooters.

 

[Steve Blair]

1) I have purchased a Hornady Lock n Load OAL Gauge and Comparitor. I was planning on using a bullet from LOT 2 (above question) to check the rifling depth. Just to confirm above, I should use a LOT 2 bullet when gathering this data point?

2) I have purchased a Forster Ultra Micrometer Seater Die. Do I zero the Micrometer to the seating depth that is measured with the Hornady Lock n Load when the bullet is touching the Rifling, or at the backed off values (.020 - ??)? I would think it would make sense to base it off of whatever depth when the bullet touches the rifling; this would then allow me to make easy and accurate seating adjustments for the backed off values?

3) When I am ready to seat a bullet from Lot 3, I would need to back out my die, via the Micrometer, by one thousandth of an inch (as it is .001 longer than LOT 2)? By doing this, would I technically be increasing the OAL of the cartridge by .001?

This is where my mind is having trouble getting around the BGC tool and usage. I am trying to understand this, but I seem to be just going through the "proper" motions. Help?

Thanks,
Mike

[br]
1. Any would do, but I usually start with the mean or largest sub-lot. [br]
2. When you run your seating depth test, use bullets from your chosen sub-lot and determine what seating depth provides the best grouping. The dimension that matters is cartridge base to ogive or distance of bullet from rifling leade. [br]
3. Yes, maintain the same cartridge base to ogive distance, regardless the sub-lot. That is technically correct, but even trimmed and pointed bullets vary a few thousandths in length to the meplat. Ignore it.

 

[Kyle Schultz]

I realize this thread is a little dated but I've been reading and rereading it trying to get things straight in my mind.

I've not been happy with the seating depth consistency of my 6.5x47 rounds. I'm using Lapua 123gr Scenar bullets. I'm seating with a Redding Competition die, which uses a seating sleeve, and measuring the BTO on the loaded rounds with a Hornady Bullet comparator.

Shown below is a picture with bullets sitting in both the comparator and the seating sleeve.



What's obvious is that the sleeve is indexing on the bullet much further up the nose than does the comparator. The comparator is indexing much closer to where I would think the bullet would actually contact the lands in the barrel.

It's my understanding that the BGC measures the distance between the ogive of the bullet (theoretically 0.256") and the bullet tip. If that's true, how can the BGC help me achieve more consistent seating depths? It seems to me that the BGC is only applicable if my seating die uses a stem (Forster for instance) rather than a sleeve.

 

[Jet]

Kyle

It measures the distance between the ogive and the point on the bullet that the seating stem contacts the bullet.

Rich

 

[jlow]

Re: BGC question

I just tested this (like, literally this week), after being certain I was right about needing to pre-sort by bearing surface or base-to-ogive. People I trust told me I was wasting my time, but I wanted to be right so I set out to prove it.

I could find no material difference between pre-sorting/BGC sorting, and BGC sorting alone. I'm not sorry to discard a practice that consumed a *lot* of my time that I've proved, to my satisfaction, provides no material benefit.

Don't waste your time pre-sorting before using the BGC. Use the BGC first, last, and only.

Jay one thing the Berger CO said that I too have found to make sense is there are at least two reasons to sort bullets by BTO.

One is if you are worried that there is significant variation and that it affects the performance of your load.

Assuming that you do not believe the above, the second reason is for QA i.e. you use it to find "bad" bullets from the batch. This I have personally found. These are bullets which are not slightly off in this measurement but way off and sometimes so far off that you can visually see that they are bad. Others are not so obvious. So with this method, you are not batching but throwing out the bad bullets because you know they will do terrible things to your precision.

 

[Kyle Schultz]

Kyle

It measures the distance between the ogive and the point on the bullet that the seating stem contacts the bullet.

Rich

Well that's the point of the question. If the BGC indexes off where the stem contacts the tip/upper nose of the bullet but my seating die uses a sleeve that contacts the bullet significantly further down the nose, the measurement is meaningless.

It seems to me (and I may be wrong) is that the BGC is useful for only gauging if the profile (based on the assumption that the profile is directly correlative to the distance between 2 points) of a bullet is consistent with that of it's brethern. I wonder if that's akin to weighing an empty case and equating that measurement with the case volume. It's pretty well established that's an invalid correlation.

But if the BGC measurement is indicative of bullet performance, it must be in terms of how consistently the bullet flies as compared to the other bullets in the box. I can't see where it would help me in the achieve a more consistent seating depth. This is what I'm trying to understand.

 

[dmoran]

Above is a picture of a bullet that I colored black with a Sharpie. Held flat and slid length ways across 400 sand paper, to show the actual bearing surface length of the bullet.
Then locked a caliper at the listed desired diameters, inserted the bullet to contact at those diameters on the bt, ogive, and nose, then spinning the bullet to scribe the lines.

Next picture below, I placed reference lines and letters to identify them by:

My own way is 3 measurements of qualification for lengths:
1 - from A to E for a first qualification
2 - from A to F for a second qualification
3 - the tare length between E and F is my final qualification of the lengths (which is what the Bob Green Comparator measures).

My reasoning is, I want consistent bullets to seating length, with relevance to BtO qualification 1st.
I personally find nil variance until after D (end of bearing) and don't concern myself with anything up to D for these reasons.

Just my way and why,
Donovan

 

[Kyle Schultz]

Donovan:

Your posting is very helpful.

Using your reference points, I thought the BGC is measuring the distance between G and E. Do I have that wrong?