Consistant seating depth...

[Pete Wass]

I discovered a long time ago that most seater stems are wrong. I experimented until I use a 30 Cal stem to load 6mm and 358 to load 30's . What matters is where the ogive will engage the lands. It is possible to load rounds that are exactly the same length, I do it every time I load.

I had a conversation with an engineer at one of the die companies. He said they were aware of the issue with the stem situation but did not want to retool or words to that effect. A stem should touch the ogive close to where the bullets will engage the lands to get consistency. Some lots of bullets are more uniform than others but there are very few perfectly consistent ogive lengths.

 

[jelenko]

I’m guessing your seating them quite deep to accomplish that, I’ve not shared that experience using 103 -108 class bthp but there’s always the exception.

It's with 223 bullets when loading for AR15 mag length. I've recently bought PRI mags for some extra length.

 

[20PPC]

I finished up loading what I needed for next week's match at Palmetto, finally ! !
I measured oal of the remaining bullets I have and ended up with a variance of .012 which I sorted into 4 groups hopefully this will help.

 

[gunsandgunsmithing]

Got another stem to try for grins? I've had a redding stem to crack and do that but not a wilson.

 

[Longtrain]

Lots of good measurement advice above…IMO the bullets can vary in different places, resulting in different lengths.
Food for thought…if you’re measuring to have a specific place in relation to the lands. With most 6mm Improved cartridges your distance to the lands is going to grow about .004” every 100 rounds, so as you shoot and if you don’t adjust the sealing depth you’ll be missing your mark where you fell accuracy is best.
(I have found that it really doesn’t matter on the target, but that’s me, other shooters mileage may vary)

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[William Vogel]

I finished up loading what I needed for next week's match at Palmeto, finally ! !
I measured oal of the remaining bullets I have and ended up with a variance of .012 which I sorted into 4 groups hopefully this will help.

That’s a lot of variation. I don’t usually see more than +/-0.001. Every once in a while I’ll get 0.003.

 

[SSchnd]

Agree with checking the seating stem with magnifying glass, the stem seating cone may have a micro crack allowing the cone to expand providing mixed seating depths, easy to check. I keep an extra stem on hand, If I hear or get a sticking snap when pulling the handle back up I know my stem has cracked. It will be very hard to see with out magnifying view.
Ask me how I know.

 

[fisherman987]

I want to say again in order to help you the best I can, in order to get the closest consistency possible without a ton of bullet sorting, I urge you to start by sorting all your bullets from the same lot by bullet overall length in groups that fall within .002 or .003 at the most. Keep them identified in zip lock baggies. When you load for a match or when you are doing load development only load using bullets from the same baggie. When you sort by overall length, you will see how dramatic a difference you'll find from bullet to bullet.

 

[Henryrifle]

If you are using premium brass (Lapua) and great projectiles (Berger) and using a quality press and quality dies and having seating depth issues that measure .004 to .010 different and you are not seating into the donut or using a compressed load then you almost surely have a neck tension issue or very inconsistent neck friction issue resulting from over cleaning the brass. If you are cleaning in stainless steel media, you can also experience peened necks that, if not addressed, would contribute to this issue.

Hank

 

[K22]

Have you actually tested these reloads on target? Do you really need that kind of seating depth precision? Just asking.

Before I jumped "off the cliff" with all kinds of equipment and prolong processes I would at least do some shooting and see if you current reloading equipment / procedure is producing reloads within your acceptable accuracy requirements.

 

[wkdickinson]

I think what you are experiencing is the difference between where the seating stem contacts the ogive and where your comparitor contacts the ogive. I had the same problem for a long time. One day I turned a new comparitor insert on the lathe to as close a diameter as I could measure to the seating stem. Using the new insert, the lengths were very consistent. IMO the underlying cause for this, is inconsistency in the ogive "profile".

 

[powderbrake]

Call up L E Wilson and order a VLD seating stem for your seating die. The standard die comes with a standard seating stem, and the VLD seating stems are for VLD Secant or Tangent/VLD Blend.

 

[ShtrRdy]

I finished up loading what I needed for next week's match at Palmeto, finally ! !
I measured oal of the remaining bullets I have and ended up with a variance of .012 which I sorted into 4 groups hopefully this will help.

This sounds to me like you are measuring to the tip of the bullet. If this is true then you can expect a large variation in length.

 

[Ned Ludd]

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:



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.

 

[jelenko]

I want to say again in order to help you the best I can, in order to get the closest consistency possible without a ton of bullet sorting, I urge you to start by sorting all your bullets from the same lot by bullet overall length in groups that fall within .002 or .003 at the most. Keep them identified in zip lock baggies. When you load for a match or when you are doing load development only load using bullets from the same baggie. When you sort by overall length, you will see how dramatic a difference you'll find from bullet to bullet.

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

 

[marchx]

I finished up loading what I needed for next week's match at Palmeto, finally ! !
I measured oal of the remaining bullets I have and ended up with a variance of .012 which I sorted into 4 groups hopefully this will help.

Hi, I am experiencing the same problem as you.

I load 6BR and using Lapua brass after 3rd firing my seating force variance seems significantly higher than before (I assume about 30% on average). This results in inconsistent seating depth. My seating depth variance in population of 30 round in the above case s is .003 on average. It's unacceptable for my assumed standard- I aim at .001 variance.

In order to combat the first problem- inconsistent neck tension manifesting via seating force variance you have to either master the annealing process or buy new brass. I chose the second scenario. Neck tension consistency lasts up to 3rd firing.

Let's say you don't have fresh brass and you do not anneal. you just want to get the consistent seating depth. I use an arbor press and Wilson seating die- I anticipate .003 variance and start seating bullets .003 longer than final CBTO and adjust the seating depth in second step if needed.

 

[jelenko]

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.

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.

 

[6Creed73]

Consistent seating depth almost always comes down to brass prep in my experience. I don't sort my bullets and my seating depth is rarely more than .0005 variance. If your brass necks aren't consistent, there will be variations in drag/pressure as the bullet seats which will cause inconsistent seating depth. This is something I've spent a lot of time working on. In my experience, these are the things that help with consistent seating depth.

1. Anealing
2. Consistent chamfer with slight bevel
3. Graphite or Neolube inside of neck
4. Mandrel as last step before seating. Use the mandrel just before seating

I was about to load some up so decided to record it and put my money where my mouth is....I can do this all day and get an extreme spread of .0005. I can't express enough how much difference it makes to use the mandrel right before seating.

 

[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.