Is there an alternative to the Accuracy One Seating Depth Comparator?

[JEFFPPC]

Bobs tool measures only a bullet from one ogive to a wider ogive, in an attempt to sort out variance in shape. It has nothing to do with a loaded round or brass

David

He made two tools. I have and use them both.

 

[padom]

I should probably keep this to myself ( and I usually delete these post after a few days) but I really prefer not using a caliper or switching back and forth while measuring from the case head. the A-1 set up is fast and accurate to .0005 for checking each round as seated, the best I’ve used in a decade. It may ease the cost to know the indicator can be used with their other tools with just a body swap.

My exact setup. I have 2 actually. One for primers and one for seating depth. Super fast, no calipers.

 

[LRPV]

Sorry to inform ya,
Read Post #5
I understood what he meant to begin with
---
Everyone - Read the title
The OP stated "Seating Depth"
He wants to be able to measure CBTO


not shoulder bump, a few people are confusing the two

Actually, the title of this thread is as follows…

Is there an alternative to the Accuracy One Seating Depth Comparator?​

In case you don’t know how that tool works, it measures from the case shoulder to ogive on the bullet. It does this job very well and very accurately. The man who designed the tool shoots in actual benchrest competitions and generally whoops everyone’s ass. Lol.

Now, it probably doesn’t measure from the exact shoulder datum and not to the exact seater stem contact or lands contact on the ogive either but when using carefully sized brass and good bullets, it does its comparative measuring job quite well and to answer the OP question about an alternative to this particular tool, no. I don’t believe there is an alternative that does what this tool does.

 

[jimmymac]

I never used a seating depth tool that measures from a datum on the shoulder of the case to the ogive of the bullet so please forgive my ignorance when I ask why that is a better method for seating depth? I am having a hard time wrapping my head around that one because in my world when I size cases, my shoulder bump is not identical on all sized cases. Close, but no cigar! So it stands to reason that if the shoulder bump dimension varies from case to case, then the measurement from that point to the ogive will also vary using a tool that measures in this fashion. Am I then fiddling with my seater die from case to case to chase the desired shoulder datum to ogive dimension I’m after? None of this makes sense to me.

 

[William Vogel]

I never used a seating depth tool that measures from a datum on the shoulder of the case to the ogive of the bullet so please forgive my ignorance when I ask why that is a better method for seating depth? I am having a hard time wrapping my head around that one because in my world my when I size cases, my shoulder bump is not identical on all sized cases. Close, but no cigar! So it stands to reason that if the shoulder bump dimension varies from case to case, then the measurement from that point to the ogive will also vary using a tool that measures in this fashion. Am I then fiddling with my seater die from case to case to chase the desired shoulder datum to ogive dimension I’m after? None of this makes sense to me.

Your shoulder bump should stay within +/-0.0005 if your brass and brass prep is consistent. Mine does. I also see no advantage to using datum to ogive if datum is derived from case head and 0ed to produce a different number used for multiple cases. Seems like stacking tolerances. Getting down on the ogive where rifling contact occurs also seems dangerous because the bullet taper at this point would be low enough that the effort to close the measurement device could “press” the bullet into the gauge at different depths easily unless the effort pressure was made consistent with a measurement gauge also. The feel of jamming a bullet into the lands during chambering vs touch or jump is hardly noticeable. My ammunition is consistent enough and proven at short range that external ballistics impart more inconsistencies in POI than internal ballistics. I’m still between 3/4 to 1/2 MOA at 700 and 800 yards using a Hornady comparator. I do all my own chambering and rifle setup in house. Bedding, assembly and machine work.

 

[jimmymac]

Your shoulder bump should stay within +/-0.0005 if your brass and brass prep is consistent. Mine does. I also see no advantage to using datum to ogive if datum is derived from case head and 0ed to produce a different number used for multiple cases. Seems like stacking tolerances. Getting down on the ogive where rifling contact occurs also seems dangerous because the bullet taper at this point would be low enough that the effort to close the measurement device could “press” the bullet into the gauge at different depths easily unless the effort pressure was made consistent with a measurement gauge also. The feel of jamming a bullet into the lands during chambering vs touch or jump is hardly noticeable. My ammunition is consistent enough and proven at short range that external ballistics impart more inconsistencies in POI than internal ballistics. I’m still between 3/4 to 1/2 MOA at 700 and 800 yards using a Hornady comparator. I do all my own chambering and rifle setup in house. Bedding, assembly and machine work.

My shoulder bump variation is within normal limits for what I am trying to achieve, so my question still stands.

 

[ELR LVR]

I never used a seating depth tool that measures from a datum on the shoulder of the case to the ogive of the bullet so please forgive my ignorance when I ask why that is a better method for seating depth? I am having a hard time wrapping my head around that one because in my world when I size cases, my shoulder bump is not identical on all sized cases. Close, but no cigar! So it stands to reason that if the shoulder bump dimension varies from case to case, then the measurement from that point to the ogive will also vary using a tool that measures in this fashion. Am I then fiddling with my seater die from case to case to chase the desired shoulder datum to ogive dimension I’m after? None of this makes sense to me.

Agreeing with this ^^^
---
The Sinclair Comparator nut gives exact CBTO numbers every time.
---
Since the seating operation pushes at the base of the case in the shellholder
Id rather take my seating depth measurements from the same spot since that is a constant
the shoulder is not a constant, the mouth is not even a constant
only the base / very bottom is.
---
It's like measuring cartridge OAL a different way than from base to tip
Why overcomplicate something simple by throwing possible variables in?
the Bullet is also chambered from the base to where the ogive meets the rifling
That is the number I need to know how far off or into the lands I am.
That is where I believe it is best to measure

 

[JFrank]

No one is over complicating the task, it’s simplifying ..
The A-1 may not be of value to some fella’s and that’s fine but for myself it’s not only faster but it’s eliminating the calipers and comparators from the equation and the minor variations and uncertainty that goes with them.
If you’re happy with the current seating results for your applications then by all means carry on.

 

[marchboom]

Some very interesting takes on this subject. Gives me concerns to think about.

Thanks

 

[LRPV]

I want to preface this by saying I'm not 100% that measuring with this tool is the best way to do it or not but as mentioned before, the guy that invented this tool has won damned near all there is to win in 600 BR over the last couple years and hasn't done too bad at 1k either.

I always see these claims that guys are bumping every piece of their brass to the .0005" and I'm going to admit that I don't get that kind of consistency. I've got a couple of different ways to manage that task and none of them are very consistent for me.

What I can be very accurate and consistent with is bullet seating from base of case to ogive on the bullet. I use the best long range bullet on the planet, sort them a little bit and rub them just right while doing my best at prepping brass. For argument sake, lets say that my base to ogive measurements are all perfect and exactly the same. Now, when I chamber that round every one of those bullets will be sitting in the exact same place in relation to the lands. IF we can all agree that the firing pin will shove the round forward until the shoulder contacts the chamber. Say you have .002" variance in your shoulder bump, you now have introduced a seating depth variance of .002"

What this tool can do in this scenario is let you sort out any headspace discrepancies and group those together or relegate the outliers to sighters.

The other part of using this tool is speed. I can probably measure 2-3 rounds in the time it would take me to measure with the NUT or other comparator attached to my calipers.

I hope this helps. I didn't proofread it. Have to go unload a truck. Keep the thread going. it's always nice to learn how people do their thing.

 

[HTSmith]

I want to preface this by saying I'm not 100% that measuring with this tool is the best way to do it or not but as mentioned before, the guy that invented this tool has won damned near all there is to win in 600 BR over the last couple years and hasn't done too bad at 1k either.

I always see these claims that guys are bumping every piece of their brass to the .0005" and I'm going to admit that I don't get that kind of consistency. I've got a couple of different ways to manage that task and none of them are very consistent for me.

What I can be very accurate and consistent with is bullet seating from base of case to ogive on the bullet. I use the best long range bullet on the planet, sort them a little bit and rub them just right while doing my best at prepping brass. For argument sake, lets say that my base to ogive measurements are all perfect and exactly the same. Now, when I chamber that round every one of those bullets will be sitting in the exact same place in relation to the lands. IF we can all agree that the firing pin will shove the round forward until the shoulder contacts the chamber. Say you have .002" variance in your shoulder bump, you now have introduced a seating depth variance of .002"

What this tool can do in this scenario is let you sort out any headspace discrepancies and group those together or relegate the outliers to sighters.

The other part of using this tool is speed. I can probably measure 2-3 rounds in the time it would take me to measure with the NUT or other comparator attached to my calipers.

I hope this helps. I didn't proofread it. Have to go unload a truck. Keep the thread going. it's always nice to learn how people do their thing.

Well said. At least now I understand.

 

[DHuffman]

I think that's as simple an explain as possible @LRPV well said.

I've used the A1 tool for several years. Someday maybe something better will come along and I'll try it with an open mind but I'll never go back to the base to ogive method.

The most important thing about using the tool IMHO is NOT trying to somehow reconcile/verify shoulder to ogive with base to ogive...
That area between the base and the shoulder IS in fact the inconsistency we are trying to take out of the process.

 

[DLT]

What is the theoretical gain of using shoulder days to give datum???
Look to the most accurate shooters process. Make sure shoulder bumps are repeatable and seating depth is repeatable! Rest is just adding time and cost!! And probably not adding any accuracy.

I wonder the same too. Not the first I have heard about measuring from the shoulder to the bullet ogive. I just don’t understand. If you know how much your bumping and where your touch point is are the main things……. to me anyways

 

[DHuffman]

Here's the part I don't understand. People who have not tried this and clearly do not understand it still maintain vehemently that the old way is better, simpler and costs less.

If someone could explain this in simple terms I can understand that'd be awesome LOL

 

[DHuffman]

Agreeing with this ^^^
---
The Sinclair Comparator nut gives exact CBTO numbers every time.
---
Since the seating operation pushes at the base of the case in the shellholder
Id rather take my seating depth measurements from the same spot since that is a constant
the shoulder is not a constant, the mouth is not even a constant
only the base / very bottom is.
---
It's like measuring cartridge OAL a different way than from base to tip
Why overcomplicate something simple by throwing possible variables in?
the Bullet is also chambered from the base to where the ogive meets the rifling
That is the number I need to know how far off or into the lands I am.
That is where I believe it is best to measure

I don't really know what to say to you at this point.
It's been explained fairly well in my opinion. I've used the shoulder method for several years and used it in competition with a fair amount of success.

I can honestly look back and see where this method brought an incredible increase in seating consistency and my match results noticably improved at the same time.

Yet you as a person who clearly has never tried it and doesn't understand it continues to tell people they are wrong and your way is better.

im just going to say I disagree with everything you say above in this post because I have used both methods being discussed and can speak from experience.

The shoulder is more of a constant than the entire case concerning the touch point/ogive

The distance between the ogive and shoulder is much shorter than the case base to ogive, that alone makes it more consistent and eliminates any inconsistencies between the shoulder and the base.

 

[DHuffman]

I never used a seating depth tool that measures from a datum on the shoulder of the case to the ogive of the bullet so please forgive my ignorance when I ask why that is a better method for seating depth? I am having a hard time wrapping my head around that one because in my world when I size cases, my shoulder bump is not identical on all sized cases. Close, but no cigar! So it stands to reason that if the shoulder bump dimension varies from case to case, then the measurement from that point to the ogive will also vary using a tool that measures in this fashion. Am I then fiddling with my seater die from case to case to chase the desired shoulder datum to ogive dimension I’m after? None of this makes sense to me.

The first thing you have to do is "take the leap of faith" that the shoulder to ogive is more constant than base to ogive by eliminating most of the case from the measurement.

Then as Jason said you have to accept the firing pin puts the case shoulder onto the chamber shoulder. If you can accept that then all that remains is the distance from the shoulder to the ogive.

By fiddling with the seater all we're doing is adjusting the seating depth to the case not the lands.
By your own admission your shoulder bump is not as consistent as you'd like, mine either so I take that out of the measurement eliminating that variable.

 

[Silo1616]

This sentence is the key to this discussion:

"IF we can all agree that the firing pin will shove the round forward until the shoulder contacts the chamber."

Seems logical, but is their proof this is happening?

 

[WSnyder]

Seems logical, but is their proof this is happening?

The people using the tool suggest that measuring shoulder to ogive and maintaining that as the constant has given them better results which suggests the case shoulder is being pushed against the shoulder of the chamber. I don’t see what else might explain their results.

 

[JFrank]

This sentence is the key to this discussion:

"IF we can all agree that the firing pin will shove the round forward until the shoulder contacts the chamber."

Seems logical, but is their proof this is happening?

we don’t have transparent chambers, but we do have trace evidence of the phenomenon see post # 51

when we size cases for our comp chambers we’re creating about .002 headspace, putting that into perspective that’s approx a human hair between the bolt face and case head, when the firing pin strikes the primer the combustion begins, now whether the pin drives the case forward or instantaneous expansion forces the case shoulder to the chamber shoulder doesn’t really matter because the fact remains it gets there and when .001 difference in seating depth can change the long range target I want to be confident of accurate and consistent seating depth from shoulder to ogive.

 

[DHuffman]

The people using the tool suggest that measuring shoulder to ogive and maintaining that as the constant has given them better results which suggests the case shoulder is being pushed against the shoulder of the chamber. I don’t see what else might explain their results.

Seems like a reasonable deduction from an open minded individual!

I honestly can't prove that the firing pin drives the case shoulder to the chamber shoulder but when I find my off the lands point using a dummy round that freely chambers that in my opinion leaves only the shoulder contact.

This is kinda where the leap of faith comes in. Just because you can't prove something's happening doesn't mean it's not happening.

I'm open to reasonable explanations to the contrary from anyone with actual experience using the method. Regardless my experience and results have told me all I need to know at this point.