Vertical with powder / Horizontal with seating depth

[CharlieNC]

Discussions related to ladder testing, ocw, etc nearly always include "choose powder charge for minimal vertical, then tune horizontal with seating depth". Historical posts show numerous examples of positive compensation and the nodes for vertical, but I don't ever remember seeing any followup selection of seating depth for horizontal uniformity; group size yes, but not specifically horizontal. I ask because when I run a ladder (typically 2-3 shots each charge) I nearly always find the effect on horizontal poi follows what is happening with vertical poi so the charge node for both is the same. Then my followup with seating depth shows relatively minor optimization for group sizes, but no specific tuning for horizontal alone. Are there occasions when something else is going on that I have not observed, or is this axiom for horizontal tuning more of an urban legend?

 

[seymour fish]

Discussions related to ladder testing, ocw, etc nearly always include "choose powder charge for minimal vertical, then tune horizontal with seating depth". Historical posts show numerous examples of positive compensation and the nodes for vertical, but I don't ever remember seeing any followup selection of seating depth for horizontal uniformity; group size yes, but not specifically horizontal. I ask because when I run a ladder (typically 2-3 shots each charge) I nearly always find the effect on horizontal poi follows what is happening with vertical poi so the charge node for both is the same. Then my followup with seating depth shows relatively minor optimization for group sizes, but no specific tuning for horizontal alone. Are there occasions when something else is going on that I have not observed, or is this axiom for horizontal tuning more of an urban legend?

Assuming long range and a set up that demonstrates positive compensation, it has been suggested here that tuning for a group shape taller than it is wide is advantageous

 

[Milo 2.0]

Discussions related to ladder testing, ocw, etc nearly always include "choose powder charge for minimal vertical, then tune horizontal with seating depth". Historical posts show numerous examples of positive compensation and the nodes for vertical, but I don't ever remember seeing any followup selection of seating depth for horizontal uniformity; group size yes, but not specifically horizontal. I ask because when I run a ladder (typically 2-3 shots each charge) I nearly always find the effect on horizontal poi follows what is happening with vertical poi so the charge node for both is the same. Then my followup with seating depth shows relatively minor optimization for group sizes, but no specific tuning for horizontal alone. Are there occasions when something else is going on that I have not observed, or is this axiom for horizontal tuning more of an urban legend?

I think I am following you, you're saying the spread each way is close to identical?
If so, try adding some neck tension, I threw the .002" rule out a long time ago and rarely take a measurement today. I've brought in more groups at distance in with neck tension after shooting an ocw at 500 yards.
I am not a benchrest shooter, just an average joe, do what you may with the advice.

 

[mikecr]

I call BS on it.
If you do actual full seating testing, you will see nothing 'minor' about seating, and that there is no directional trend other than overall opening & closing to grouping.

Yeah, I've also seen the generalizations about discounting horizontal in ladders. Don't do that.
A barrel, and where it points, and where it throws bullets, is not just up & down. Hell the entire shooting system moves, and every bit of that system, including your rests, affects POI. If you rest a thumb on the tang, you can throw shots 1" @500yds. Will that be horizontal or vertical? It could be any direction.

 

[Terry]

Discussions related to ladder testing, ocw, etc nearly always include "choose powder charge for minimal vertical, then tune horizontal with seating depth". Historical posts show numerous examples of positive compensation and the nodes for vertical, but I don't ever remember seeing any followup selection of seating depth for horizontal uniformity; group size yes, but not specifically horizontal. I ask because when I run a ladder (typically 2-3 shots each charge) I nearly always find the effect on horizontal poi follows what is happening with vertical poi so the charge node for both is the same. Then my followup with seating depth shows relatively minor optimization for group sizes, but no specific tuning for horizontal alone. Are there occasions when something else is going on that I have not observed, or is this axiom for horizontal tuning more of an urban legend?

Tony Boyer and Gene Beggs have written on this. It's real. Jam your bullets and shoot at 100. you will see two holes side by side. As you seat them deeper this will go away.

 

[mikecr]

Just 'jam your bullets' and you'll have 2 holes side by side....WOW
And there was no qualification behind that assertion?

 

[CharlieNC]

Turns out all the bullets I shoot like jump, but that is a bit of a tangent. Mainly I'm questioning the oft quoted " powder for vertical, depth for horizontal" without having ever seen an example of the application, given I have not observed it myself.

 

[BoydAllen]

I know a well respected shooter who tends to favor the LT powders and he soft seats with quite a bit of success.

 

[butchlambert]

I spoke with a shooter from Oklahoma, Darrell Loker I believe, and he did extensive testing in a tunnel. As I remember it, Darrell said either neck tension affected horizontal and bullet seating depth affected vertical. This was the last thing that he adjusted after getting his best load.

 

[mikecr]

The only time you could observe this or that -and assert anything about it, is when you've thoroughly removed every abstract except for the adjustment in question, and qualified that assertion(every bit of it).
So 2 holes beside each other with a jam seating of a 6PPC can mean pretty much diddly to a 300WSM with different bullets, seated elsewhere, and 20kpsi lower in pressure.

I know we don't have every answer yet, but before accepting folklore, shouldn't we ask ourselves WHY it would be this way,, and then IF it applies under other circumstances.
For decades mob consensus was that VLDs had to be jammed to shoot well. Yet, all it took was an actual seating test to prove otherwise for many. That's someone wondering IF it was true, or hogwash.

 

[Bart B.]

Tony Boyer and Gene Beggs have written on this. It's real. Jam your bullets and shoot at 100. you will see two holes side by side. As you seat them deeper this will go away.

Sounds plausible if someone can explain the physics involved to change how the barrel vibrates different in the horizontal axis. Until then, I'm skeptical. I've jammed a couple thousand bullets into the lands and horizontal stringing equaled free chambered ones same load and rifle. Zero changes a little that's all.

Out of square case heads cause horizontal shot stringing 3 to 9 o'clock with 2 lug bolts in battery with a lug at 6 and 12 o'clock in the receiver ring. Bullets jammed or free seated, same horizontal spread.

 

[MagnumManiac]

As Mikecr said, where the barrel points is not linear to up and down.
The barrel oscillates in vibration, which is an oval pattern, whether it’s up and down, side to side or diaganol to bore line is not out of the question. In fact, as velocity increases the oscillation is changing, which is why we shoot for the tightest round group.

In a ladder, horizontal at the same elevation is what I look for, it matters not, at the first instance, if the shots are 4-6” apart, it’s the elevation that matters.

I honestly don’t believe that seating depth changes horizontal in most instances. I can say that I have never seen it myself, if I understand correctly, that bullets that group side by side suddenly move into a circular group by changing seating depth. I have seen changing seating depth bring ALL shots in closer, but this is different to my mind.

Cheers.

 

[Dusty Stevens]

I think the wind is more responsible for horizontal dispersion than anything. Without windflags and the knowledge to use them has caused many a sleepless nights chasing gremlins. Just putting one in your backyard to watch while you sit in a chair is an eye opener.

 

[6BRinNZ]

I call BS - unless someone can clarify with harmonic theories that seating depth will only affect horizontal. Then I would post my pictures of seating depth tests.
I've got powder charges that show strips, shrinking groups out to a strip and similar with seating depth. this makes sense to me as I don't see how any one change can only affect the bullet exit in only one plane (horizontal)

 

[dmoran]

Here's a 1000yd seating ladder (4-thousandth increments):


Red +.006" /\ Blue +.010" /\ Green +.014"

 

[JimSC]

I have been reading Boyers Rifle Accuracy book lately and find his ideas in chapter 22 and 23 concerning horizontal and vertical stringing interesting.

Here are two different bullets , same rifle, different day. 70 Nosler RDF and 80 Berger VLD. You can see the transition on the Vertical to horizontal then back to vertical with the Nosler. The Bergers seemed to love .075 jump as well as .010 into the lands. Both had bad horizontal at .025. Both are long high BC bullets

 

[mikecr]

There is a big difference between actual seating testing, and mere group shaping with minor tweaking of seating inside a window (like an 8thou beyond touching).
This may be a source of disconnect in these discussions.

I consider actual/full seating testing to be similar to Berger's recommended. This is the coarse adjustment to results, and the affects are way beyond any powder adjustments(which are fine).

After powder/ladder testing, the grouping can be shaped with minor wiggles of seating inside it's window. This is no more or less to development significance than adjusting powder +/- a couple kernels, or adjusting neck grip length +/- 10thou. Not that these adjustments are equivalent in results, nor insignificant, just that they're smaller in adjustment potentials than broad declarations qualify to support.
For example, a vast notion that 'seating = horizontal' would likely fail too many tests to be at all believable. After all, truths pass all tests, and anybody who's done full seating testing has seen the notion would not pass tests.

Now if someone declared that with[xx/yyy/zz.zzz] system they can tweak some or remaining horizontal out with minor seating adjustment? That's a whole lot easier to believe.
And if someone countered "I can tweak out some or remaining vertical with minor seating". That's believable too.

 

[ClassCat]

No one takes wind into consideration.

 

[JimSC]

I still have 80 of those Noslers left, sometime this summer I want to try to tweak that Nosler .025 load in .005 increments up and down and see if the groups tighten and second test leaving it a .025 off and tweaking the powder charge.

 

[JFrank]

I call BS - unless someone can clarify with harmonic theories that seating depth will only affect horizontal. Then I would post my pictures of seating depth tests.
I've got powder charges that show strips, shrinking groups out to a strip and similar with seating depth. this makes sense to me as I don't see how any one change can only affect the bullet exit in only one plane (horizontal)

6BR in NZ
I'm going with you on this one.
Tuning loads is fickle, I get tighter groups with seating not just horizontally but vertical as well I may have to go back and forth a couple of times , I'm always concerned with wind and mirage skewing test however when I hit the magic load nothing seems to effect it. I had a test going yesterday in horrible conditions I almost went back home rather I stuck it out fearing the worst but at the end - there it was 1.25 at 550
Go figure
SPJ