Seating depth changing?

[MJN030]

Sorry. Check all the bullets you are loading and sort based on ogive I guess . It is possible that ogive measurement is not 100% the same from bullet to bullet out of the same box.

Im out .

Have a nice day.

 

[Huntnful]

Ok. You do you .

If you don't want to understand it, that's fine. I wasn't being insulting, just explaining your misunderstanding is all.

 

[Dean2]

If the brass measures say 3.214" for example,
And the next one measure 3.218" and the next one is 3.216" then when you seat the bullet the depth of the bullet will be different .

Trim all of your empty cases to the shortest piece of brass you are trying to load .
Again, these are hypothetical numbers in this discussion .

But trim ALL of your cases to the same length is what I'm trying to say.

I'm sure you've already done this . But it is something to look at .

Thanks
Marc

Ok. You do you .

This is not a case of you do you!. Some things are opinion or preference, some things are facts. 2+2=4 is not an opinion or preference. Your favourite color is. @Huntnful is right, your statement that different neck lengths affects COAL is simply wrong. Neck length, or varying neck lengths, have nothing to do with OAL or COAL and that is a fact, not an opinion.

If you post things that are wrong and someone takes the time to correct you, learn from it, rather than puffing up and trying to defend something that isn't right. The internet has a ton of wrong info on it and it is growing rapidly. Lets try not to add to it here on LR Hunting.

 

[Pops Fitch]

As mentioned, back off a tiny bit and adjust for each load…..or for precise seating depth get yourself an in-line seater and arbor press……IF that couple of thousands difference bothers you that much.

Love my Forster equipment for exact and repeatable loads where the Dillon does the fun loads and pistol load work. It's ok to have more than one machine. I personally have 7 including shotgun equipment. What makes it really easy is a change out system such as Inline Fabrication.

 

[MJN030]

This is not a case of you do you!. Some things are opinion or preference, some things are facts. 2+2=4 is not an opinion or preference. Your favourite color is. @Huntnful is right, your statement that different neck lengths affects COAL is simply wrong. Neck length, or varying neck lengths, have nothing to do with OAL or COAL and that is a fact, not an opinion.

If you post things that are wrong and someone takes the time to correct you, learn from it, rather than puffing up and trying to defend something that isn't right. The internet has a ton of wrong info on it and it is growing rapidly. Lets try not to add to it here on LR Hunting.

Look . I wasn't trying to "puff up "
The topic of discussion was around why his seating depth was changing I merely asked if the length of the shells were all the same .

I do understand it . You are using a comparator to measure from the bottom of the shell to the ogive of the bullet .

The ogive of the bullet could be different from one bullet to another in the same box .

Certainly they will be very close to each other but that was not the question .

This is not a case of you do you!. Some things are opinion or preference, some things are facts. 2+2=4 is not an opinion or preference. Your favourite color is. @Huntnful is right, your statement that different neck lengths affects COAL is simply wrong. Neck length, or varying neck lengths, have nothing to do with OAL or COAL and that is a fact, not an opinion.

If you post things that are wrong and someone takes the time to correct you, learn from it, rather than puffing up and trying to defend something that isn't right. The internet has a ton of wrong info on it and it is growing rapidly. Lets try not to add to it here on LR Hunting.

Maybe there is a misunderstanding here .


When you're measuring seating depth by CBTO (Cartridge Base To Ogive), you're measuring from the case head to a specific point on the bullet's ogive using a comparator insert—not to the bullet tip.

This method is much more consistent than measuring overall length (COAL), but it still isn't perfect. Small variations from one loaded round to another are normal.

Here are the main reasons CBTO can vary:

1. Bullet-to-bullet ogive variation

Even premium bullets are manufactured with tolerances. The comparator contacts the bullet at a specific diameter on the ogive, and that point may not be located in exactly the same position on every bullet.

For example, a box of match bullets might vary by ±0.001–0.003 inch in CBTO before seating. Hunting bullets can vary even more.

This is why two cartridges seated with the same die setting can produce slightly different CBTO measurements.

2. Seating stem contact point

The seating stem inside the die rarely contacts the bullet at the exact same point as your comparator insert.

The seating stem typically pushes on a larger area of the ogive near the nose. If the bullet shape varies slightly, the stem can push different bullets to slightly different positions.

This effect is more noticeable with:

• Polymer-tipped bullets
• Secant-ogive bullets
• Soft-point hunting bullets

3. Case shoulder position (headspace variation)

CBTO is measured from the case head. If your cases don't all have identical shoulder positions after sizing, your CBTO measurements will vary even when the bullet is seated identically relative to the case mouth.

For example:

• Case A shoulder datum: 2.0540 inches
• Case B shoulder datum: 2.0555 inches

If both bullets are seated to the same depth relative to the neck, the measured CBTO of the loaded rounds will differ by 0.0015 inch.

This is one reason precision reloaders carefully control shoulder setback.

4. Neck tension differences

Variations in:

• Neck wall thickness
• Inside neck diameter
• Annealing consistency
• Lubrication inside the neck

can change how much resistance the bullet encounters during seating.

Greater resistance can sometimes cause the bullet to seat slightly differently.

5. Press and die alignment

Minor variations in:

• Shellholder dimensions
• Press flex
• Ram alignment
• Case runout

can create small differences in seating depth.

6. Measurement technique

The comparator tool itself can introduce variation.

Inconsistent caliper pressure, failing to fully seat the comparator insert, or measuring at a slight angle can easily create ±0.001 inch differences.

 

[82nd Bill]

Look . I wasn't trying to "puff up "
The topic of discussion was around why his seating depth was changing I merely asked if the length of the shells were all the same .

I do understand it . You are using a comparator to measure from the bottom of the shell to the ogive of the bullet .

The ogive of the bullet could be different from one bullet to another in the same box .

Certainly they will be very close to each other but that was not the question .



Maybe there is a misunderstanding here .


When you're measuring seating depth by CBTO (Cartridge Base To Ogive), you're measuring from the case head to a specific point on the bullet's ogive using a comparator insert—not to the bullet tip.

This method is much more consistent than measuring overall length (COAL), but it still isn't perfect. Small variations from one loaded round to another are normal.

Here are the main reasons CBTO can vary:

1. Bullet-to-bullet ogive variation

Even premium bullets are manufactured with tolerances. The comparator contacts the bullet at a specific diameter on the ogive, and that point may not be located in exactly the same position on every bullet.

For example, a box of match bullets might vary by ±0.001–0.003 inch in CBTO before seating. Hunting bullets can vary even more.

This is why two cartridges seated with the same die setting can produce slightly different CBTO measurements.

2. Seating stem contact point

The seating stem inside the die rarely contacts the bullet at the exact same point as your comparator insert.

The seating stem typically pushes on a larger area of the ogive near the nose. If the bullet shape varies slightly, the stem can push different bullets to slightly different positions.

This effect is more noticeable with:

• Polymer-tipped bullets
• Secant-ogive bullets
• Soft-point hunting bullets

3. Case shoulder position (headspace variation)

CBTO is measured from the case head. If your cases don't all have identical shoulder positions after sizing, your CBTO measurements will vary even when the bullet is seated identically relative to the case mouth.

For example:

• Case A shoulder datum: 2.0540 inches
• Case B shoulder datum: 2.0555 inches

If both bullets are seated to the same depth relative to the neck, the measured CBTO of the loaded rounds will differ by 0.0015 inch.

This is one reason precision reloaders carefully control shoulder setback.

4. Neck tension differences

Variations in:

• Neck wall thickness
• Inside neck diameter
• Annealing consistency
• Lubrication inside the neck

can change how much resistance the bullet encounters during seating.

Greater resistance can sometimes cause the bullet to seat slightly differently.

5. Press and die alignment

Minor variations in:

• Shellholder dimensions
• Press flex
• Ram alignment
• Case runout

can create small differences in seating depth.

6. Measurement technique

The comparator tool itself can introduce variation.

Inconsistent caliper pressure, failing to fully seat the comparator insert, or measuring at a slight angle can easily create ±0.001 inch differences.

Good write up and I agree with this. I would only add that the primer seating can affect CBTO readings. If the primer is seated above the case head the CBTO will indicate longer than it really is.

 

[Bitteroot]

A seating comparator that gauges off the case shoulder to a similar contact point as the seater die has proven to be the most accurate I've seen or used. Of course it always helps when you're using good bullets that have a consistent nose geometry. lol without that we might as well just not worry about seating changes

 

[dstancu]

Good write up and I agree with this. I would only add that the primer seating can affect CBTO readings. If the primer is seated above the case head the CBTO will indicate longer than it really is.

That is a possibility, but primer seating protruding over the case head is actually dangerous, a no-no, exposing the most sensitive part of the cartridge to bumps that can set the hole thing alive. In that case, forget about CBTO and accuracy, one may get hurt or have property damaged!
The primer should be slightly below the case surface, even if just for a few thousands, for safety reasons.
There is a very simple test to avoid that situation: if you set the cartridge upright on a flat surface , it should be very stable, no wobble at all. Of course, you can also measure the depth with an instrument. If not, you may have an exposed primer, even if it's not discernable by just looking at it.

 

[dstancu]

A better caliper won't give you more consistent readings and analogue is not less accurate than digital if you can see the graduations. How you use them is what creates consistency. Jaws 90 degrees to what you are measuring, measure at exactly the same place, and use the same pressure on the thumb wheel. I have Micrometers that measure to .00005 and consistency is even more important with them.

Best bullet puller by far is the Hornady press mounted system. Fast, accurate and the bullets are reusable.

View attachment 762333

You can get a power version for your Lyman that uses a battery powered drill to turn the cutter. Have used one for years. Lyman with power adaptor.

View attachment 762334

If you do lots of trimming they have a self powered version.

View attachment 762335


The same applies to using powder throwers and seating bullets. Using the exact same sequence, stroke, speed and pressure, are all critical to consistency and will impact the consistency of the outcome.

Agreed, a good bullet puller is a must have in my view. I was frustrated by the cheap inertia (hammer) bullet puller and its shortcomings. I looked around for reviews and opinions, and bought the RCBS bullet puller. It is a bit slower to set and operate than the Hornady cam-lock type, but it seems built somewhat stronger.
Both are way better for repeated use, and preserving components for re-use. Once mounted, you can pull about 10 bullets per minute, and you are less wary to experiment further with loads and seating depths. If you reach some limits (e.g. pressure), you can easily re-use what you decide to not fire.

 

[robert rex]

Use a LE Wilson micrometer in-line seating die. Using an AMP press I've seated bullets that were at 90psi and 175psi and they both measure exactly the same base to ogive. Strangely enough when fired at 100 yrds the both went thru the same hole and were within 10ft/sec of each other. If you move a LE Wilson die .0005 deeper it will seat .0005 deeper....exactly. Now does seating depth matter? Absolutely, that's why your seating tool has to be excellent.

 

[MagnumManiac]

I would like to interject here regarding COMPARATOR TOOLS of any description.
To trust them in ANY way as being ACCURATE is foolhardy. They are NOT accurate measuring tools, they're thwart with misalignment, wrong dimensions both in height, hole diameter and OD. If you measure the slot accurately, you will easily see no 2 are the same.
Use them as intended, compare several pieces across the entire batch and take an average, especially on CBTO, it will make barely a difference on target beyond 600 unless the discrepancy is large, like above .005".
Averages of .002"+/- are neither here nor there in the grand scheme of things.

Cheers.

 

[Bitteroot]

For those whom desire taking their program to the next level, the little things do matter and affect the target to a degree.
Sorting non custom bullets can be time consuming and somewhat maddening but for those that do wish to take the plunge I'll point out a couple of things.
The relationship between the bullet ogive and seater contact point ( nose geometry ) is very important simply because when we adjust the seater .001 we want the ogive to throat relationship to move .001 as well so with that in mind I start by sorting base to seater stem contact point using a comparator approx the same diameter as the stem.
I sort those into batches of .002 then sort the best of those by base to ogive into .002 batches.
I take the best of those and sort them by overall length for long range competition.
At 1000 yards overall length does indeed make a difference.
I did this for a few years a finally just started buying custom bullets and only sort by overall length now.
I'm much happier and so are my targets.

Coming full circle to seating variations~ If your intentions are to shoot small at long range, seating depth matters.

Stay centered
B