Seating depth…what does it do?

[kthomas]

With all of your years as a test shooter for manufacturers, are you willing to share your knowledge and experience? I’m seriously curious to hear your opinions.

I'm not a test shooter for manufacturers, you must have me mistaken for someone else.

 

[kthomas]

Yes it matters. Here's what it looks like in pictures. Two-shot groups.


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Classic example of using sample sizes that have no statistical relevance in which we can draw conclusions from.

I don't mean this to offend, it seems all reloaders are guilty of this. As a community, we have an abhorrent understanding of statistics and statistical analysis, which leads to very flawed conclusions.

 

[Jager]

Classic example of using sample sizes that have no statistical relevance in which we can draw conclusions from.

I don't mean this to offend, it seems all reloaders are guilty of this. As a community, we have an abhorrent understanding of statistics and statistical analysis, which leads to very flawed conclusions.

No offense taken.

Statistics are relevant in some places. Not in others.

When I'm running a seating depth test I'm not at all looking for statistical confirmation. I'm mostly looking for all those loads that don't work - which is most of them.

Two shots is ridiculous from a statistical standpoint, of course. But once that second shot has edged out away from the first, the group isn't going to get any smaller. And I don't need to see any more.

Which is not to say that once I see a two-shot "group" that look promising I call it a winner and call it a day. The load(s) that look promising will most certainly get their chance to prove their repeatability. Or not.

 

[Acyr]

Classic example of using sample sizes that have no statistical relevance in which we can draw conclusions from.

I don't mean this to offend, it seems all reloaders are guilty of this. As a community, we have an abhorrent understanding of statistics and statistical analysis, which leads to very flawed conclusions.

What if he could replicate this test multiple times? Would it matter then? All reloaders are not guilty of this. As a statistical expert you should know better than to draw those conclusions.

 

[kthomas]

What if he could replicate this test multiple times? Would it matter then? All reloaders are not guilty of this. As a statistical expert you should know better than to draw those conclusions.

I'm certainly not a statistical expert (I seem to get mistaken for someone else on this specific forum frequently).

Replication is key. If those tests were conducted 10, 20, 100+ times with identical results, that would certainly be a better data set to draw conclusions from. There are certainly limitations to the test however, such as the degree of precision to which the seating depths really are, taking into account any error of the operator and the degree of precision of said calipers, amongst other things. There's also limitations to how the testing is done, specifically from the shooter side - there'll certainly be induced error, which would be impossible to parse out with such small data sets.

And this hypothesis of bullets coming into and out of "nodes" - what is the explanation for that? What is the mechanism that allows that happen? There seems to be a lot of conjecture around what the projectile is doing and what's influencing its behavior. No one is quite able to really explain that. I would love to see some detailed and scientifically conducted tests on this, rather than the observational/anecdotal data of low quality that we always see.

All that said, I would be very interested in seeing this test duplicated many times over, to see if the results repeated themselves consistently.

 

[gunsandgunsmithing]

I haven't chased lands in a bbl since I started using tuners in about 2007. That should answer the question a lot of people have here...."in bore time"...or exit time relative to muzzle position...That's tuning in a nutshell.

 

[Acyr]

I'm certainly not a statistical expert (I seem to get mistaken for someone else on this specific forum frequently).

Replication is key. If those tests were conducted 10, 20, 100+ times with identical results, that would certainly be a better data set to draw conclusions from. There are certainly limitations to the test however, such as the degree of precision to which the seating depths really are, taking into account any error of the operator and the degree of precision of said calipers, amongst other things. There's also limitations to how the testing is done, specifically from the shooter side - there'll certainly be induced error, which would be impossible to parse out with such small data sets.

And this hypothesis of bullets coming into and out of "nodes" - what is the explanation for that? What is the mechanism that allows that happen? There seems to be a lot of conjecture around what the projectile is doing and what's influencing its behavior. No one is quite able to really explain that. I would love to see some detailed and scientifically conducted tests on this, rather than the observational/anecdotal data of low quality that we always see.

All that said, I would be very interested in seeing this test duplicated many times over, to see if the results repeated themselves consistently.

I agree that higher sample rates are usually more valid statistically. However, there are shooters out there that are qualified to shoot small samples and get accurate data. I don't know @Jager qualifications as a shooter but to dismiss his results outright is a mistake.
As far as nodes go it is a simple matter of harmonics. Shoot enough test groups and you will be enlightened.
I learned early on in life that speaking in absolutes only served to make me look uneducated.
You don't know what you don't know.

 

[kthomas]

I agree that higher sample rates are usually more valid statistically. However, there are shooters out there that are qualified to shoot small samples and get accurate data. I don't know @Jager qualifications as a shooter but to dismiss his results outright is a mistake.
As far as nodes go it is a simple matter of harmonics. Shoot enough test groups and you will be enlightened.
I learned early on in life that speaking in absolutes only served to make me look uneducated.
You don't know what you don't know.

That's the whole point of my post - we generally talk in absolutes despite a lack of quality data that would otherwise allow us to do so. What I'm saying is that there isn't enough information to draw any conclusions from those tests, there's nothing absolute about that.

And I'm sure Jager is a good shooter. We shouldn't conflate shooting skills with statistical analysis, the two are independent of each other.

On its own, the data that Jager presented is essentially meaningless. If it can be replicated over and over and over again, then it may mean something (though there are obvious shortcomings we have to recognize). But that data presented on its own is meaningless. 5+ years ago I would've agreed with the analysis whole heartedly, but with the numerous shooting and testing I've done over the past few years, I need much more data before I can draw any conclusions. The more I shoot and test things, the more I realize how meaningless small sample sizes are, and how much myth and lore there truly is in this sport.

 

[davidjoe]

That higher peak pressure when jamming or touching the lands, relative to jumping, isn’t just harder on the brass, it’s necessarily harder on the throat and the first portion of the barrel.

That first steel that the bullet encounters is straining and stretching under extreme pressure restricting the bullet, is nearly the only thing holding it back (along with its own inertia) and is a very small surface area of steel being acted upon.

One could consider all the cumulative case head wear and deformation of every piece of brass fired through a barrel, and the forces stretching and widening the single throat, as two sides of the same coin.

 

[Steve Blair]

I shot this seating depth test 28 October. Rifle is a BAT 3LL in a Manners F-Class stock, 34" Brux 9.75" twist, Ø1.25" straight, .300WSM with .280" freebore. Load is 66.5 grains H4831SC of a slightly slow lot behind Berger 230 Hybrids. Velocity is ~2850 with 5-shot groups ~8 fps ES. The numbers in the boxes are CBTO. My other rifles in 6 BR and .284 Shehane do not behave like this. My .300 WSM (through several barrels from two vendors) is exceptionally tolerant to charge weight and seating depth.

 

[BoydAllen]

That higher peak pressure when jamming or touching the lands, relative to jumping, isn’t just harder on the brass, it’s necessarily harder on the throat and the first portion of the barrel.

That first steel that the bullet encounters is straining and stretching under extreme pressure restricting the bullet, is nearly the only thing holding it back (along with its own inertia) and is a very small surface area of steel being acted upon.

One could consider all the cumulative case head wear and deformation of every piece of brass fired through a barrel, and the forces stretching and widening the single throat, as two sides of the same coin.

A good friend has found that for his rifles that throat erosion is more jumped than with bullets seated into the rifling. Your thing about higher pressures ignores the fact that most of us work up our loads with a seating depth, starting low. We do not take a load that is already on the warm side and go from jump to touch or into the rifling. We work it up in the rifling. As far as brass life goes, you can get to high pressures jumping. It is a matter of burn rate and charge weight.

 

[BoydAllen]

On the two shot test and statistics thing, The very best of components and rifles (good enough to compete in registered benchrest competition) tend to repeat very well. The two shot method is not to produce a final result but to spot where you should test using more shots per group. None of us who have done this really care about the opinions of the statistics bunch (Yes I did have a college course and really do understand sample size.) because we have done it successfully many times, and IMO results trump theory every time. If you are testing a good rifle, shooting over flags, with good wind conditions, and there is paper between two bullet holes at 100 yards, adding more shots will not make the group smaller.

 

[Dusty Stevens]

On the two shot test and statistics thing, The very best of components and rifles (good enough to compete in registered benchrest competition) tend to repeat very well. The two shot method is not to produce a final result but to spot where you should test using more shots per group. None of us who have done this really care about the opinions of the statistics bunch (Yes I did have a college course and really do understand sample size.) because we have done it successfully many times, and IMO results trump theory every time. If you are testing a good rifle, shooting over flags, with good wind conditions, and there is paper between two bullet holes at 100 yards, adding more shots will not make the group smaller.

And if that horrendous 2 shot group wasnt you or the wind theres no need in testing it again

 

[BoydAllen]

I never found seating depth to be a significant element in developing accurate loads. I'm referring to the seating depths often reported in published reloading data for specific bullets, especially in the Sierra and Nosler reloading manuals.

My seating depth rules are: first, the overall length of the cartridge must fit the magazine, second, the OAL must be at least .010" from the lands to prevent jamming a bullet into the lands, and third, the OAL must allow for at least one bullet diameter to be inserted into the neck in order to provide sufficient neck tension. This has worked for me for as long as I have been reloading.

The most significant element I've found in producing accurate reloads is the selection of the bullet assuming you're using a powder that is suitable for the cartridge that you are loading for.

I do not know of any competiton shooter who would refer to a loading manual for seating depth....none.

 

[K22]

I do not know of any competiton shooter who would refer to a loading manual for seating depth....none.

I don't follow them either, instead I apply the rules I stated. It's just that I've never found that varying seating depth made much difference in group size. However, I don't load or shoot to the level of those top competitors, and I would always defer to them because of the ultimate precision that they achieve.

What I have discovered is that the bullet can really make a big difference. For example, I've done some extensive load testing for the 87 Vmax Hornady bullets in my 243's when I couldn't obtain my favorite bullet, the 85 Sierra BTHP. No matter what I tried, powder charge, different powder, primer, seating depth, etc. that bullet just wouldn't shoot well in my Custom Hart Barrel Rem Model 7, Browning X bolt and Rem 700. Yet, it shot ok in my Tikka T3X. When I say wouldn't shoot well I'm talking about 1 1/2 to 1 3/4 moa, well above my standard of 1/2 to 5/8" moa.

 

[BoydAllen]

I don't follow them either, instead I apply the rules I stated. It's just that I've never found that varying seating depth made much difference in group size. However, I don't load or shoot to the level of those top competitors, and I would always defer to them because of the ultimate precision that they achieve.

What I have discovered is that the bullet can really make a big difference. For example, I've done some extensive load testing for the 87 Vmax Hornady bullets in my 243's when I couldn't obtain my favorite bullet, the 85 Sierra BTHP. No matter what I tried, powder charge, different powder, primer, seating depth, etc. that bullet just wouldn't shoot well in my Custom Hart Barrel Rem Model 7, Browning X bolt and Rem 700. Yet, it shot ok in my Tikka T3X. When I say wouldn't shoot well I'm talking about 1 1/2 to 1 3/4 moa, well above my standard of 1/2 to 5/8" moa.

Do you ever seat bullets so that they are longer than touch?

 

[Turpentine]

I only know that I am far too ignorant to contribute anything meaningful here when it comes to the ”Why”. Compared to most of you guys, I’m basically the equivalent of a poorly trained space ape and that’s on a good day. No offense implied to space apes, they do a hell of a job and have my admiration. I only know that once I find the sweet spot for the powder I’m using and velocity range the rifle seems to prefer, changes in seating depth make groups bigger or smaller. Sometimes dramatically so. I tend to gravitate toward the smaller. Carry on!!!

 

[Bill Norris]

I only know that I am far too ignorant to contribute anything meaningful here when it comes to the ”Why”. Compared to most of you guys, I’m basically the equivalent of a poorly trained space ape and that’s on a good day. No offense implied to space apes, they do a hell of a job and have my admiration. I only know that once I find the sweet spot for the powder I’m using and velocity range the rifle seems to prefer, changes in seating depth make groups bigger or smaller. Sometimes dramatically so. I tend to gravitate toward the smaller. Carry on!!!

I totally agree with you. Once powder type and charge is established in either of my rifle load testing then seating depth either in or out of the lands changes group size.

 

[Turpentine]

On the two shot test and statistics thing, The very best of components and rifles (good enough to compete in registered benchrest competition) tend to repeat very well. The two shot method is not to produce a final result but to spot where you should test using more shots per group. None of us who have done this really care about the opinions of the statistics bunch (Yes I did have a college course and really do understand sample size.) because we have done it successfully many times, and IMO results trump theory every time. If you are testing a good rifle, shooting over flags, with good wind conditions, and there is paper between two bullet holes at 100 yards, adding more shots will not make the group smaller.

I get it. Makes sense. If you can shoot. The only fly in that ointment is it may not apply to people who shoot like me. Very poorly to worse at times. Sometimes so poorly it even surprises me. A good many of my shots are followed by mild expletives and complete wonder.
All BS aside. If my 1st two aren’t good, adding another doesn’t generally make things any better. The only one time I may re address that particular charge weight and seating depth is if my chronograph numbers are really consistent for those first two.

 

[K22]

Do you ever seat bullets so that they are longer than touch?

No, never. The reason is that I'm a hunter first and foremost. I can't afford to have a bullet lodge in the lands when I extract an unfired round.

Had this happen once due to me inadvertently seating an 85 Sierra BTHP too long. In my Tikka and Browning, the ogive of this bullet is such that I cannot seat it anywhere the Sierra book value or SAMMI max COL. I have to seat at 2.620 to be .010" off the lands. Anyway, the bullet stuck in the lands, and I ended up with powder in the mag well - a mess. Fortunately, I carry a cleaning rod in the truck and was able to knock the bullet out, so it didn't ruin my hunt.