Seating by ogive or COAL?

[kyotekiller25]

I have a couple questions here. So to start, I've been shooting long range, mainly 1K for the past 25 years, mainly hunting rifles and just 3 shot groups. In the beginning I seated to same COAL. As time progressed I started seating to the ogive. These days I can pretty much hold 4-6" 3 shot group at 1K laying prone/rear bag with my rifles. Which is good enough for me and what I'm doing anyway. I make sure all my rounds are identical to the ogive seating depth, after sorting bullets from longest to shortest, then starting out with the shorter ones I seat to the ogive I need, and turn the seater die down for the longer ones until they all match up ogive wise. It is a pretty lengthy and tedious process.

But, now a days I am almost more confused as when I started. I see people seating to COAL, versus the ogive and saying it's more accurate at long range. How can that be? I understand the BC part of it, but at the same time don't you want them all the same ogive/correlation to the lands also? You can't have both can you?

Its kinda hard for me to put this in words but if a guy seated all bullets to the same COAL, wouldn't there be a .001"-.010" difference in the ogive, or whatever variance is in the box of bullets at that point? Or vice versa by seating all to the same ogive, there'd be whatever difference in COAL due to the difference in overall bullet lengths?

Seems to me your always going to have up to say maybe a .010" variance in either ogive or COAL at that point, so which is typically more accurate at 1K+? Would love to hear from some of you better more experienced long range shooters on this and get some clarification, or at least how you do thing anyway.

Hoping I somewhat made sense rambling on here. Or maybe I'm just over thinking it all and just need to continue doing it the way I have been since I am still getting 1/2 MOA at 1K pretty routinely.

Thanks!

 

[Straightshooter1]

I have a couple questions here. So to start, I've been shooting long range, mainly 1K for the past 25 years, mainly hunting rifles and just 3 shot groups. In the beginning I seated to same COAL. As time progressed I started seating to the ogive. These days I can pretty much hold 4-6" 3 shot group at 1K laying prone/rear bag with my rifles. Which is good enough for me and what I'm doing anyway. I make sure all my rounds are identical to the ogive seating depth, after sorting bullets from longest to shortest, then starting out with the shorter ones I seat to the ogive I need, and turn the seater die down for the longer ones until they all match up ogive wise. It is a pretty lengthy and tedious process.

But, now a days I am almost more confused as when I started. I see people seating to COAL, versus the ogive and saying it's more accurate at long range. How can that be? I understand the BC part of it, but at the same time don't you want them all the same ogive/correlation to the lands also? You can't have both can you?

Its kinda hard for me to put this in words but if a guy seated all bullets to the same COAL, wouldn't there be a .001"-.010" difference in the ogive, or whatever variance is in the box of bullets at that point? Or vice versa by seating all to the same ogive, there'd be whatever difference in COAL due to the difference in overall bullet lengths?

Seems to me your always going to have up to say maybe a .010" variance in either ogive or COAL at that point, so which is typically more accurate at 1K+? Would love to hear from some of you better more experienced long range shooters on this and get some clarification, or at least how you do thing anyway.

Hoping I somewhat made sense rambling on here. Or maybe I'm just over thinking it all and just need to continue doing it the way I have been since I am still getting 1/2 MOA at 1K pretty routinely.

Thanks!

The problem with referencing to other people's CBTO is the differences in the caliper insert as there's often a significant difference in the measurement, just as there is with a cartridge's COAL. However, I think one can compensate for COAL by finding a corresponding bullet of the came OAL and using you're own caliper insert to determine the corresponding CBTO.

Unless you're seating to touch or jam, you really don't want to "chase the lands" as the correlation of the CBTO to the lands really isn't very important as seating depth is. This is why as they throat erodes, one can go for a very long throat erosion distance before ever having to make any adjustments to seating depth.

If you really want to get uniform seating depths, consider where you're seating stem contacts the ogive verses where you're caliper insert contacts the ogive. Seating depth is determined by where you're seating stem contacts the ogive, not where the typical CBTO is measured.

 

[kyotekiller25]

The problem with referencing to other people's CBTO is the differences in the caliper insert as there's often a significant difference in the measurement, just as there is with a cartridge's COAL. However, I think one can compensate for COAL by finding a corresponding bullet of the came OAL and using you're own caliper insert to determine the corresponding CBTO.

Unless you're seating to touch or jam, you really don't want to "chase the lands" as the correlation of the CBTO to the lands really isn't very important as seating depth is. This is why as they throat erodes, one can go for a very long throat erosion distance before ever having to make any adjustments to seating depth.

If you really want to get uniform seating depths, consider where you're seating stem contacts the ogive verses where you're caliper insert contacts the ogive. Seating depth is determined by where you're seating stem contacts the ogive, not where the typical CBTO is measured.

Makes a little sense, kinda. So by that you're saying to go by the COAL at that point and not the ogive, correct?

 

[CNC-Dude]

If you watch the podcast between Brian Litz and Erik Cortina this topic is discussed by them. It depends on the type of bullet you are using. If you are using an open tip bullet, then sorting them by OAL will make more of a difference at 1000 yards than by seating them by ogive.

 

[JFrank]

At minimum sort your quality bullets by OAL into batches of .001-.002
Using a quality die and comparator, confirm your seating depth by CBTO, ensure all the case neck prep is the same and trust the seater to do its job but varify results.
Know your seating window because as the throat erodes you may or may not want to advance the depth that equal amount.

 

[Orr89rocz]

If you sorted the bullets by base to ogive and then also by overall length as it base to tip, then cartridge oal and cartridge base to ogive on the comparator should be pretty close to same across the board

A box of bergers can vary as much as 0.015” in oal. Usually tighter for the majority in the same box. I sort them by oal to within 2-3 thousandths. Base to ogive seems to not vary much for me for a lot of bullets. Maybe .001. So technically everything should be held within 2-4 thousandths oal when seating to cbto. It seems to work ok for me.

 

[SeabeeKen]

When seating bullets of varying lengths to the same COL or CBTO it would seem to me to have more or less bullet inside the case which would vary pressure. Doesnt seem to be very consistent. Why not sort bullets into groups of same length which will give same CBTO and COL and protrusion into the case.

 

[kyotekiller25]

If you watch the podcast between Brian Litz and Erik Cortina this topic is discussed by them. It depends on the type of bullet you are using. If you are using an open tip bullet, then sorting them by OAL will make more of a difference at 1000 yards than by seating them by ogive.

I shoot ELDMs in all my rifles. The variance in bullet length and ogives can be usually anywhere from .005"-.010" in a box in my experience.

I just ordered 3 Forster Ultra Micrometer seater for each of my rifles, 223, 6 Creed, 7-300 Win Mag also. Been using the basic RCBS seater and I'm throwing those in the trash...Absolute garbage consistency with ELDMs.

 

[JFrank]

Make sure the ELDM tips are not making contact with the seater stem.

 

[Jeff Porter]

Let me throw you another curve ball. I have been having more success getting smaller rounder groups with lower SD and ES by seating to a seating depth inside the case. I see more consistency on paper by controlling the internal ballistics of the case. With a seater die that is made for the profile of the bullet I am using, I try to control the seating depth and not worry about jump to lands/ CBTO or the COAL. I check the bullet base to ogive and keep that under 0.002" variation. There is a risk that the bullet profile may vary between individual bullets such that the distance between the comparator contact point and the seater contact may vary more than 0.002" but I have not seen that as a huge problem with the .224 and .243 Berger's I am shooting. More variation in length on the bullets seems to occur from the seater stem contact point to the tip.

Ned has posted images of what I am talking about recently.

 

[Liven The Dream]

At minimum sort your quality bullets by OAL into batches of .001-.002
Using a quality die and comparator, confirm your seating depth by CBTO, ensure all the case neck prep is the same and trust the seater to do its job but varify results.
Know your seating window because as the throat erodes you may or may not want to advance the depth that equal amount.

Well said...............

 

[6Creed73]

I have a couple questions here. So to start, I've been shooting long range, mainly 1K for the past 25 years, mainly hunting rifles and just 3 shot groups. In the beginning I seated to same COAL. As time progressed I started seating to the ogive. These days I can pretty much hold 4-6" 3 shot group at 1K laying prone/rear bag with my rifles. Which is good enough for me and what I'm doing anyway. I make sure all my rounds are identical to the ogive seating depth, after sorting bullets from longest to shortest, then starting out with the shorter ones I seat to the ogive I need, and turn the seater die down for the longer ones until they all match up ogive wise. It is a pretty lengthy and tedious process.

But, now a days I am almost more confused as when I started. I see people seating to COAL, versus the ogive and saying it's more accurate at long range. How can that be? I understand the BC part of it, but at the same time don't you want them all the same ogive/correlation to the lands also? You can't have both can you?

Its kinda hard for me to put this in words but if a guy seated all bullets to the same COAL, wouldn't there be a .001"-.010" difference in the ogive, or whatever variance is in the box of bullets at that point? Or vice versa by seating all to the same ogive, there'd be whatever difference in COAL due to the difference in overall bullet lengths?

Seems to me your always going to have up to say maybe a .010" variance in either ogive or COAL at that point, so which is typically more accurate at 1K+? Would love to hear from some of you better more experienced long range shooters on this and get some clarification, or at least how you do thing anyway.

Hoping I somewhat made sense rambling on here. Or maybe I'm just over thinking it all and just need to continue doing it the way I have been since I am still getting 1/2 MOA at 1K pretty routinely.

Thanks!

When you say you see people seating by COAL...are you sure people aren't just referencing COAL when discussing a load?

For example, I measure CBTO when seating bullets because it's much more consistent, but if I'm discussing a load I reference COAL because my CBTO measurement is useless to anyone other than myself. There are too many different caliper inserts and even the same manufacturers can have variations with exactly where the insert measures the ogive. For that reason, I always use COAL when sharing load data.

 

[Straightshooter1]

Makes a little sense, kinda. So by that you're saying to go by the COAL at that point and not the ogive, correct?

Not exactly.

When I'm trying to get some idea of someone's cartridge seating depth, I'll want to know the COAL. Though a bullet's OAL can vary quite a bit, I'll try to use a bullet that has an OAL listed in QuickLoad or some reloading manual and load it into a dummy cartridge to the person's stated COAL. Then I'll take my caliper and measure the CBTO to get some idea, based on my particular caliper insert, what the seating depth is that's been stated for that COAL. It's still not very precise since bullet BTO's can vary as well. But this technique tends to give me some idea of where that person's CBTO is relative to my own caliper insert, which I find better than just trying to go by anyone's stated CBTO.

 

[kyotekiller25]

So for example here I'll use my 223 with 75g ELDMs.

My COAL to the lands is 2.510" I seat to 2.5" or .010" off

With my calipers and hornady comparator, my base to ogive measurement is 1.94" which is what I seat all my bullets to. Not the actual 2.5" as that varies a few thousandths here or there based on the length of the bullet, but my base to ogive measurements are all dead nuts at 1.94"

That's how I do it anyway. But when I say I see some guys seating to COAL, that just means I'd seat them all to 2.5" which, which would then mean I'd have inconsistencies at the ogive length. Seems either way you go, you're going to have some sort of inconsistency on one end or the other at the end of it.

If that makes sense. I'm off work with broken fingers, so I have way too much time on my hands lately, and probably overthinking things haha.

I just wanted to know which way is more accurate downrange, seating all the same from base to ogive, or base to bullet tip.

I've been doing base to ogive the last few years and it seems to be shooting better than base to tip, for me. 3 shot 1/2 MOA or 5 shot 3/4 MOA at 1K is plenty good for what I'm doing anyway, so I guess it's working.

I've even won a local PRS type match out to 1100 with my 7-300 Win Mag and 180g ELDMs, so I guess I'll just continue seating all the same from base to ogive, and let the overall length to the tips just be what it is at this point...

 

[Evan]

if you think about the firing pin pushing the case into the chamber, up against the shoulder before finally igniting the primer, you might conclude the best way to maintain the exact same bullet to barrel lands configuration would be to measure and control the distance from bullet ogive to shoulder datum, rather than OAL or BTO.

 

[Straightshooter1]

So for example here I'll use my 223 with 75g ELDMs.

My COAL to the lands is 2.510" I seat to 2.5" or .010" off

With my calipers and hornady comparator, my base to ogive measurement is 1.94" which is what I seat all my bullets to. Not the actual 2.5" as that varies a few thousandths here or there based on the length of the bullet, but my base to ogive measurements are all dead nuts at 1.94"

That's how I do it anyway. But when I say I see some guys seating to COAL, that just means I'd seat them all to 2.5" which, which would then mean I'd have inconsistencies at the ogive length. Seems either way you go, you're going to have some sort of inconsistency on one end or the other at the end of it.

If that makes sense. I'm off work with broken fingers, so I have way too much time on my hands lately, and probably overthinking things haha

What I was trying to explain was how I or anyone else, on the other side of this computer screen, can load up a cartridge with the same 1.94" CBTO with my comparator that's most likely very different that your comparator. My comparator could easily give me a .060" difference than yours (like the difference between a Sinclair comparator and the Hornady comparator).

Apparently, I misunderstood what you were trying to understand . . . ¯\_(ツ)_/¯

I just wanted to know which way is more accurate downrange, seating all the same from base to ogive, or base to bullet tip.

I've been doing base to ogive the last few years and it seems to be shooting better than base to tip, for me anyway. 3 shot 1/2 MOA or 5 shot 3/4 MOA at 1K is plenty good for what I'm doing anyway, so I guess it's working.

When we're talking about "seating depth" (that is, how far the base of the bullet goes into to case as measured from the base of the case), is best measured from where the seating stem contacts the ogive rather than where the typical comparator makes contact with the ogive. The difference between these two points of contact can be substantial (several thousandths), especially from one lot to another.

The typical comparator is good for finding the touch point on the lands where you can decide on a starting point for loading the cartridge (like .010 off the lands). To maintain whatever seating depth that .010 off the lands represents and do it consistently, you'll need a comparator that touches the same spot as your seating stem. Doing so, you can have variations is the CBTO (which doesn't really matter much) as the difference between those two contact points will vary. Note that using the seating stem contact point for seating depth isn't effected by variations a bullet's OAL's (base to meplat measurement).

 

[Murray Brook]

I generally always load using the CBTO measure, only thing to watch for in an hunting rifle is that they fit your magazine unless you single load.. In some hunting rifles I have the mag will not allow me to load say .015 off and fit in the magazine.

 

[K22]

COAL based on ogive that is the concept with the Frankfort Arsenal tool procedure which is what I have used for a very long time.

The procedure involves measuring the maximum COAL based on the ogive touching the lands. Because of variations in bullet ogives, caliper precision, and bullet tips, this process has some small inherent variation but is it precise enough for most shooting purposes if you do not want to sort bullets or use a bullet comparator.

Since I never seat close to the lands, most of the time about .020 to .015" or further off the lands, this procedure works quite well for me. I measure about 3 or 5 bullet from a lot and use the longest measurement as my max COAL for that bullet in that rifle.

 

[mikecr]

Your tested best seating window is about optimum ogive interface with bore, and it's huge to results.
It is independent of nose length, or bearing or base length.
It has nothing to do with seating depth in the neck.
It doesn't relate to what other people measure or recommend.

Test for best seating depth with a given bullet,, measure & log it's CBTO with any tool contacting the ogive somewhat near land contact datum(a point at least related to the bullet/bore interface),, and reproduce that.

If you want same bullet length attributes, then measure them separately.
That's totally different than setting ammo for what a gun tells you is the right CBTO.

 

[Ned Ludd]

What I was trying to explain was how I or anyone else, on the other side of this computer screen, can load up a cartridge with the same 1.94" CBTO with my comparator that's most likely very different that your comparator. My comparator could easily give me a .060" difference than yours (like the difference between a Sinclair comparator and the Hornady comparator).

Apparently, I misunderstood what you were trying to understand . . . ¯\_(ツ)_/¯



When we're talking about "seating depth" (that is, how far the base of the bullet goes into to case as measured from the base of the case), is best measured from where the seating stem contacts the ogive rather than where the typical comparator makes contact with the ogive. The difference between these two points of contact can be substantial (several thousandths), especially from one lot to another.

The typical comparator is good for finding the touch point on the lands where you can decide on a starting point for loading the cartridge (like .010 off the lands). To maintain whatever seating depth that .010 off the lands represents and do it consistently, you'll need a comparator that touches the same spot as your seating stem. Doing so, you can have variations is the CBTO (which doesn't really matter much) as the difference between those two contact points will vary. Note that using the seating stem contact point for seating depth isn't effected by variations a bullet's OAL's (base to meplat measurement).


View attachment 1540892

Nice to see you're using my pictures again without referencing the person that took the time to make that image...me.