Consistant seating depth...

[Webster]

I just started shooting mid range 600 yards and am experiencing problems getting consistant seating depth in the case.
I'm shooting a 6BRA chambered by Ronnie Long, Lapua brass, Varget, Federal primers and 105 Berger Hybrids.
I cannot get 2 bullets in a row to seat the same depth, I sent the Wilson seater stem to Ronnie because it was was not making the consistant proper contact on the bullet.
He opened it up a slight amount and polished it to what now appears to be perfect contact with the tip of the bullet.
I've measured BTO on the bullets and all of them appear to be within + - .0015 yet when seating I'll get .004 - .010. difference.
Needless to say 2 1/2 hrs later " actually longer " and only 75 rounds loaded is getting to the point the hassle of loading is outwaying the enjoyment of shooting.
Any advise would be appreciated.
Dave

Just a thought, something to think about. If your seater stem makes contact any where on the ogive a very slight change in the diameter at the point of contact might make a 5-10 thou difference in where the seater contacts the ogive? Your sliding a ring down a taper. Are we making the assumption that the seater contact is at the same location on every bullet? Maybe some geometery whiz guys could make a mathematical example. Would it make sense for the seater to contact the ogive 5-10 thou above the bearing surface. My standard Wilson micrometer seater leaves a ring contact mark in the middle of the ogive almost a 1/4" above the bearing surface. I used valve grinding comound to get the seater to better match my bullet without marking it. But this didn't change the contact location.

I think you could make an example by sliding a ring down a simple triangle taper. The math would be easy. I think i'll try it.

 

[Ned Ludd]

My understanding is the OAL of a HP bullet varies more than the BTO because of the very tip of the bullet and that the swage die controls the rest of the bullet. When I look at the tips of HP's, I see variations in thousandths just to the way/where the tip is cut.
I just inked a Hornady 68 HPBT and seated it with a Forster. The contact point is ~ 60% of the distance from the start of the ogive to the tip of the bullet.

No doubt the consistency of the bullet BTO dimension versus nose length/ogive is due to the manufacturing process. Also, the critical contact points can certainly vary in location on the bullet ogive. The image above is merely meant to illustrate the general concept of the two critical contact points and how they can affect seating depth consistency. There can also be other reasons why someones setup might not exactly mirror the image above. For example, caliper inserts from different companies do not necessarily have the same diameter holes. Likewise, seating die stems from different companies can vary, and there can also be Lot-to-Lot diametral variance of the bullet ogives at a given point. Nonetheless, we can usually improve seating depth consistency via bullet sorting and/or a rigorous step-by-step examination of the process itself.

 

[jelenko]

Just a thought, something to think about. If your seater stem makes contact any where on the ogive a very slight change in the diameter at the point of contact might make a 5-10 thou difference in where the seater contacts the ogive? Your sliding a ring down a taper. Are we making the assumption that the seater contact is at the same location on every bullet? Maybe some geometery whiz guys could make a mathematical example. Would it make sense for the seater to contact the ogive 5-10 thou above the bearing surface. My standard Wilson micrometer seater leaves a ring contact mark in the middle of the ogive almost a 1/4" above the bearing surface. I used valve grinding comound to get the seater to better match my bullet without marking it. But this didn't change the contact location.

I think you could make an example by sliding a ring down a simple triangle taper. The math would be easy. I think i'll try it.

Interesting point.
I'm asking Forster how tolerant seating depth is with changes in the shape of the ogive.

 

[6Creed73]

Bullet base-to-ogive length has little to do with maintaining consistent seating depth. In contrast, bullet nose length can have a significant impact on consistent seating depth because the two contact points critical for maintaining consistent seating depth are located on the bullet ogive. The two critical contact points are where the seating die stem contacts the bullet out toward the meplat and "pushes" it during the ram downstroke, and the point on the bullet ogive just above the top of the bearing surface where the caliper tool insert seats when we measure:

View attachment 1517589

Bullet length variance in the nose region between the two critical contact points can have an undesirable effect on seating depth consistency. In order to reduce this effect, one can sort bullets using a tool such as Bob Green's Comparator (https://greensrifles.com/new-product-page), which effectively sorts bullet by the distance between the two critical contact points. Alternatively, if the bullets used have a fairly consistent BTO dimension, then the majority of any OAL length variance will by definition reside in the nose region. Thus, one can sort bullets by OAL as sort of a poor man's Bob green Comparator, as long as the BTO dimension of the bullet is consistent.

Once any obvious potential issues with the seating die stem and/or press have been ruled out, and the bullets have been length-sorted to maximize consistency between the two critical contact points, there are still other things that can be checked or tested if the seating depth inconsistency still remains. For example, excessive neck tension (interference fit) can affect consistent seating depth, so that is probably worth checking. The use of some form of neck lubrication may also be of benefit. The bottom line is that with issues of this sort, it is often necessary to evaluate possible variables (i.e. "causes") one by one until the culprit can be found and eliminated.

I don't knock anyone for sorting bullets, I used to sort but didn't see results that were worth the time, at least not worth it to me. I think sorting has more benefit when talking about BC and long range shooting vs seating consistency...especially in the case of the OP. He said he's seeing variations of .004 to .010. Even factory seconds don't have that much variation in BTO.

 

[Evan]

It made an immediate difference in my groups when I made a tool and measured/uniformed the dimensions from case shoulder to bullet ogive. In theory, if you have bumped all your shoulders identically, then the base of case to bullet ogive would be the same, but at least in my process, it’s not. My base to shoulder measurement does wander slightly. If your shoulder to bullet ogive measurement is consistent, then the relationship of bullet to lands is consistent when the firing pin forces the case shoulder into the chamber during ignition, regardless of how far anything is from the base of the case. The accuracy one seating depth comparator is a tool that makes this measurement, if you don't have the tools to make one yourself.

 

[6Creed73]

It made an immediate difference in my groups when I made a tool and measured/uniformed the dimensions from case shoulder to bullet ogive. In theory, if you have bumped all your shoulders identically, then the base of case to bullet ogive would be the same, but at least in my process, it’s not. My base to shoulder measurement does wander slightly. If your shoulder to bullet ogive measurement is consistent, then the relationship of bullet to lands is consistent when the firing pin forces the case shoulder into the chamber during ignition, regardless of how far anything is from the base of the case. The accuracy one seating depth comparator is a tool that makes this measurement, if you don't have the tools to make one yourself.

I agree, the shoulder to bullet ogive is probably the most important measurement when it comes to seating depth/distance to lands. I've contemplated getting the Accuracy One tool several times...I need to just bite the bullet and get it.

I have their primer pocket and primer seating depth tool and it's very high quality.

 

[Straightshooter1]

Bullet base-to-ogive length has little to do with maintaining consistent seating depth. In contrast, bullet nose length can have a significant impact on consistent seating depth because the two contact points critical for maintaining consistent seating depth are located on the bullet ogive. The two critical contact points are where the seating die stem contacts the bullet out toward the meplat and "pushes" it during the ram downstroke, and the point on the bullet ogive just above the top of the bearing surface where the caliper tool insert seats when we measure:

View attachment 1517589

Bullet length variance in the nose region between the two critical contact points can have an undesirable effect on seating depth consistency. In order to reduce this effect, one can sort bullets using a tool such as Bob Green's Comparator (https://greensrifles.com/new-product-page), which effectively sorts bullet by the distance between the two critical contact points. Alternatively, if the bullets used have a fairly consistent BTO dimension, then the majority of any OAL length variance will by definition reside in the nose region. Thus, one can sort bullets by OAL as sort of a poor man's Bob green Comparator, as long as the BTO dimension of the bullet is consistent.

Once any obvious potential issues with the seating die stem and/or press have been ruled out, and the bullets have been length-sorted to maximize consistency between the two critical contact points, there are still other things that can be checked or tested if the seating depth inconsistency still remains. For example, excessive neck tension (interference fit) can affect consistent seating depth, so that is probably worth checking. The use of some form of neck lubrication may also be of benefit. The bottom line is that with issues of this sort, it is often necessary to evaluate possible variables (i.e. "causes") one by one until the culprit can be found and eliminated.

this!! ^^^^^

 

[Ned Ludd]

I don't knock anyone for sorting bullets, I used to sort but didn't see results that were worth the time, at least not worth it to me. I think sorting has more benefit when talking about BC and long range shooting vs seating consistency...especially in the case of the OP. He said he's seeing variations of .004 to .010. Even factory seconds don't have that much variation in BTO.

I routinely sort bullets by OAL for the purpose of generating more consistent points (i.e. pointing/tipping bullets). A typical Lot # of Berger bullets will have from .010" to .015" OAL variance, minimum. If one includes a small number of extreme outliers, the overall length variance is even greater. In the same bullets, the BTO variance is markedly less. Although it will depend in part on the intended application, one of the major points for sorting bullets is to remove the extreme outliers; i.e. "culling".

The OP stated that he observed as much as .004" to .015" variance in seating depth, not BTO. His reported BTO variance was +/-.0015". If a specific Lot# of bullets has nose length variance of .010" to .015", of course not all of that OAL variance will lie between the critical contact points. Thus, the effect of OAL variance will depend on the amount of length variance that actually lies between the critical contact points. Nonetheless, length variance between the critical contact points can create seating depth inconsistency. That inconsistency can be minimized by bullet OAL sorting. As always, the choice of whether to length sort bullets lies with the individual.

 

[Webster]

I routinely sort bullets by OAL for the purpose of generating more consistent points (i.e. pointing/tipping bullets). A typical Lot # of Berger bullets will have from .010" to .015" OAL variance, minimum. If one includes a small number of extreme outliers, the overall length variance is even greater. In the same bullets, the BTO variance is markedly less. Although it will depend in part on the intended application, one of the major points for sorting bullets is to remove the extreme outliers; i.e. "culling".

The OP stated that he observed as much as .004" to .015" variance in seating depth, not BTO. His reported BTO variance was +/-.0015". If a specific Lot# of bullets has nose length variance of .010" to .015", of course not all of that OAL variance will lie between the critical contact points. Thus, the effect of OAL variance will depend on the amount of length variance that actually lies between the critical contact points. Nonetheless, length variance between the critical contact points can create seating depth inconsistency. That inconsistency can be minimized by bullet OAL sorting. As always, the choice of whether to length sort bullets lies with the individual.

Do they make the seater stems as shallow cups because there cheaper to make? If the seater pushed closer to the bearing surface they would have to be much deeper cups and cost a lot more to make.

 

[6Creed73]

I routinely sort bullets by OAL for the purpose of generating more consistent points (i.e. pointing/tipping bullets). A typical Lot # of Berger bullets will have from .010" to .015" OAL variance, minimum. If one includes a small number of extreme outliers, the overall length variance is even greater. In the same bullets, the BTO variance is markedly less. Although it will depend in part on the intended application, one of the major points for sorting bullets is to remove the extreme outliers; i.e. "culling".

The OP stated that he observed as much as .004" to .015" variance in seating depth, not BTO. His reported BTO variance was +/-.0015". If a specific Lot# of bullets has nose length variance of .010" to .015", of course not all of that OAL variance will lie between the critical contact points. Thus, the effect of OAL variance will depend on the amount of length variance that actually lies between the critical contact points. Nonetheless, length variance between the critical contact points can create seating depth inconsistency. That inconsistency can be minimized by bullet OAL sorting. As always, the choice of whether to length sort bullets lies with the individual.

I agree, differences in OAL can vary much more than BTO. I may have misunderstood, but I think the OP was saying his variation in seating depth was by measuring CBTO, not OAL.

If that's the case, with a variance in bullet BTO of .0015, sorting them would have very little affect on his seating depth (CBTO) variations of .004 - .015.

But if he is measuring by OAL, I agree with you...sorting them will have an impact on his measurement. I think most serious reloaders measure seating depth By CBTO though. Or are you saying the stem contacts closer to the nose than the ogive and that where the variation may be coming from? Either way...I also shoot the 105 Hybrids and I don't sort...my seating variation is rarely more than .0005. I think there is something else going on here.

 

[Ned Ludd]

Do they make the seater stems as shallow cups because there cheaper to make? If the seater pushed closer to the bearing surface they would have to be much deeper cups and cost a lot more to make.

I don't pretend to understand the financial decisions made by companies in the reloading industry. However, I think there is a more obvious reason for the current design of seating dies. If one wanted a seating die stem that contacted and "pushed" on the bullet very close to the point on the ogive that first contacts the rifling, I believe it might necessitate having a much wider hole through the die than might be desirable. Otherwise, the metal of the seater stem itself might need to be pretty thin out near the edges. I'm guessing it could be done, as Bob Green's tool works on a similar principle. However, the fact that it has not been done across the board with seater dies suggests the manufacturers must have reasons why they have chosen not to pursue that approach.

 

[Bc'z]

Again, why sort by OAL? The dimension you want to 'control' is the BTO.

CBTO is what your after for sure.
Knowing the most variance is going to be ahead of the ogive sorting by length separates that variance into smaller groupings. Now your seater is a inanimate tool that you set to your desired CBTO providing your not bottoming out your meplat into your seater stem.
I believe you'll find a very consistent CBTO if you try it.

There was just a article in the bulletin within last 2 weeks of US Army marksmanship team doing this very method as well.

 

[Ned Ludd]

I agree, differences in OAL can vary much more than BTO. I may have misunderstood, but I think the OP was saying his variation in seating depth was by measuring CBTO, not OAL.

If that's the case, with a variance in bullet BTO of .0015, sorting them would have very little affect on his seating depth (CBTO) variations of .004 - .015.

But if he is measuring by OAL, I agree with you...sorting them will have an impact on his measurement. I think most serious reloaders measure seating depth BY CBTO though.

This has nothing to do with measuring loaded rounds using COAL. I completely agree with you that CBTO is the measurement with the greater meaning in the context of consistency and serious reloading.

Regardless, look again at the illustration I posted above. Any length variation between the critical contact points will show up as seating depth inconsistency. The seating die stem pushes against the bullet at a point farther out on the ogive toward the bullet meplat. The caliper insert seats at a point on the bullet ogive closer to the top of the bearing surface. If the nose length of bullets between those two critical contact points is not uniform (which it generally won't be unless they have been length sorted), the result will be seating depth variance consistent with the length variance between the critical contact points. It has to be that way, as the distance between the point where the seating die stem contacts and pushes the bullet into the case and the point at which we measure is fixed for a single bullet. If two different bullets have a difference distance between the critical contact points, the resultant seating depth as measured by CBTO will not be the same.

 

[6Creed73]

This has nothing to do with measuring loaded rounds using COAL. I completely agree with you that CBTO is the measurement with the greater meaning in the context of consistency and serious reloading.

Regardless, look again at the illustration I posted above. Any length variation between the critical contact points will show up as seating depth inconsistency. The seating die stem pushes against the bullet at a point farther out on the ogive toward the bullet meplat. The caliper insert seats at a point on the bullet ogive closer to the top of the bearing surface. If the nose length of bullets between those two critical contact points is not uniform (which it generally won't be unless they have been length sorted), the result will be seating depth variance consistent with the length variance between the critical contact points. It has to be that way, as the distance between the point where the seating die stem contacts and pushes the bullet into the case and the point at which we measure is fixed for a single bullet. If two different bullets have a difference distance between the critical contact points, the resultant seating depth as measured by CBTO will not be the same.

I get what you are saying now...I agree, there is probably more inconsistency on the part of the bullet where the stem contacts. It just hasn't been my experience that it's enough to affect seating depth much. I'm using the same bullet as the OP and I get very consistent seating without sorting.

I use a Whidden seating die. Later, I'll break it down and see where it contacts the bullet, because I'm curious now.

 

[Bill Norris]

Make sure you are using the same smooth stroke when seating. I can push my bullet in further if I push hard and bounce my press handle. Precision tools are fantastic but it is still important to FEEL a operation.

This has been more help in seating depth consistency than anything I've tried so far. Pressure on the press handle and no bounce at the bottom of the stroke is key at least with my Rockchucker.

 

[6Creed73]

This has been more help in seating depth consistency than anything I've tried so far. Pressure on the press handle and no bounce at the bottom of the stroke is key at least with my Rockchucker.

Agreed, no bounce or pressure at the bottom of the stroke is important. This is a reason why I like seating on a press that has a hard stop. I let it lightly hit the stop, that way I know I'm stopping the same every time.

 

[William Vogel]

I have a hard time believing that the Berger bullets are the problem. I shoot the 105 Hybrid Target and I have several thousand. I’ve never gotten these inconsistent seatings from my 6Dasher loads. I also shoot Hornady ELDM in 223AI, 6.5 Creedmoor and 308 and also get very little inconsistent seatings. I don’t know what might be happening here.

 

[wkdickinson]

Think about what we are doing with the seating die - there is an exact distance between the shell holder and the seating stem. That dimension never changes, unless you change it. However, the seating stem references in a different place than either where the bullet engages the rifling, or where the comparitor engages the ogive. Assuming you have reasonably consistent neck tension (and I'm not even sure that is all that important)and the distance between the CB and the seating stem doesn't change, then what you are dealing with is measurement error (from measuring at different places) and/or bullet form inconsistancy.

 

[Bill Norris]

Think about what we are doing with the seating die - there is an exact distance between the shell holder and the seating stem. That dimension never changes, unless you change it. However, the seating stem references in a different place than either where the bullet engages the rifling, or where the comparitor engages the ogive. Assuming you have reasonably consistent neck tension (and I'm not even sure that is all that important)and the distance between the CB and the seating stem doesn't change, then what you are dealing with is measurement error (from measuring at different places) and/or bullet form inconsistancy.

In my experience varying neck tension does have an affect on seating depth consistency.

 

[Jeff Porter]

Nomex underwear on so I can throw in my pre inflation $ 0.02.

My experience with a load shooting well as the throat erodes ( not chasing the lands ) has led me to sort bullets by BTO (base to comparator touch point ) and then control the CBTO of the loaded rounds under 0.002”. This keeps the base of the bullet at the same location in the case neck and this seating depth control has shown to be more indicative of controlling a loads tune than jump to touch point.

YMMV but this seems to be working for me.