Seating depth…what does it do?

[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.

 

[jackieschmidt]

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.

That is a great point.
As a strictly Competition Shooter, I never thought of that.

It’s not like you can just dump it on the slighter.

 

[wkdickinson]

If you ever shot thru a test barrel youd see the pressure change of the changing case volume. That may give you more of an idea of how and why it changes

I have wondered for awhile now if we aren't considering the wrong end of the bullet when talking about seating depth. I wonder if the important variable here is the variation in the case volume as it relates to how deep or shallow the bullet is seated in the case?

 

[Alex Wheeler]

As a 50/50 competitor/hunter I had a 280 ai that shot unreal jammed .020". I killed 4 elk that way. I just shoot them where they shoot best. To each his own.

 

[Turpentine]

I have wondered for awhile now if we aren't considering the wrong end of the bullet when talking about seating depth. I wonder if the important variable here is the variation in the case volume as it relates to how deep or shallow the bullet is seated in the case?

I just this week have been dealing with that very thing working up 147 eldm’s in 6.5-06. I’m touching lands at 3.40 conservatively. My sweet spot is Approx. 16 thousandths off at 3.384 There isn’t much loading info for the 6.5-06 out yet on this bullet that I could find. Hornady seats its 140 class bullets at COL 3.265. in my older manual. Hodgdon lists a 143eldx at 3.34 but I’m not sure if the ogive isnt pushed a bit farther forward in the 143 vs the 147. I should have some 143s soon to compare. Sierra lists a 155 smk at 3.30. That gave me an extra .044 to .089 difference from the seating depth the respective companies likely used to compile their pressure data. I worked up very cautiously with H4831sc, and Fed 210m and arrived at a very accurate node at 53.4-53.6 grains in 270 Winchester brass and Federal brass. This charge weight gave me single digit ES and SD. Numbers for both case types. Velocity was slightly higher in Federal which made sense because the case weight was 15 grains heavier than the Winchester. Cases didn’t show any hint of pressure nor did any of my measurements indicate excessive pressure. Bolt lift was identical, easy one finger lift just like my lightest charges. I mentioned these results and had a comment that I was likely in excess of 61K + pressure which concerned me so I asked if anyone could get me a Quickload printout with my barrel length, seating depth, case type, bullet, primer etc. I don’t want to run over pressure loads for all the obvious reasons.
The Quickload printout shows practically mirror images of my workup velocities per charge weight from 51.6 to 53.6 with pressure at 56,990 for the 53.6 charge weight. This is reassuring and at least gives me a little peace of mind. It would be interesting to compare Quickload results and subsequent pressures at the shorter, published seating depths and note barrel time changes as well.
I had almost identical results in my 308 when I installed my Wyatt bottom metal and Mag. I went from seating 2.81 to 2.86 with my bullet and a load of Varget that was showing slight pressure signs a 2.81. At 2.86 the slight pressure signs disappeared and bolt lift was normal instead of slightly stiff. Also accuracy increased significantly at 2.86.
This is likely old news to a lot of you guys. But interesting to this country bumpkin as I do not have any intentions of running over pressure loads in either rifle and wanted to make sure I was relatively safe.

 

[Jager]

Regarding pressure, and how it changes as one makes increasing changes in seating depth... here is that information for the seating depth test I uploaded in post #90:




If you start from a bullet jumping, and march towards the lands, you'll see very slight decreases in pressure and velocity at each increment, as case volume slowly increases. That will then reverse as you approach hard jam, as the bullet suddenly has much more resistance to initial movement.

Those pressure curve and velocity changes are absolutely part of the picture. But they are very, very slight for each increment of change.

Here, "Predicted Velocity" and "Predicted Pressure" are from QuickLoad. CSTO is cartridge-shoulder-to-ogive.

 

[Turpentine]

Regarding pressure, and how it changes as one makes increasing changes in seating depth... here is that information for the seating depth test I uploaded in post #90:


View attachment 1389576

If you start from a bullet jumping, and march towards the lands, you'll see very slight decreases in pressure and velocity at each increment, as case volume slowly increases. That will then reverse as you approach hard jam, as the bullet suddenly has much more resistance to initial movement.

Those pressure curve and velocity changes are absolutely part of the picture. But they are very, very slight for each increment of change.

Here, "Predicted Velocity" and "Predicted Pressure" are from QuickLoad. CSTO is cartridge-shoulder-to-ogive.

Interesting and useful info. I’m just trying to learn here. Curiosity I guess.
It would seem to me that the pressure curve would also be different for jump versus jam. Even if total pressure is the same. For jump does pressure build more slowly because of less initial resistance then increase sharply when the bullet contacts the lands? As opposed to jam where it would seem initial pressure would rise very quickly because there is increased resistance from the beginning? Of course I have no idea if that would matter but it’s still interesting