Seeking empirical evidence to support or refute powder/seating-depth nodes

[Huntnful]

I have been reloading since the early 90's and have always believed that consistency is the key to accuracy. To this end I have always tried to be meticulous with regards to seating depth, powder charge, neck tension, primers, brass and bullets. Recently I have seen some compelling evidence that challenges my long held belief that small changes in seating depth and powder charge affect accuracy to the degree I previously thought. I am still trying to sort it all out and trying to reproduce, for myself, some of the evidence I have seen from others. If I can achieve the same accuracy at reasonable seating depths (0.020" - 0.050" off the lands) then I can stop fussing with that part of the loading process and focus on other steps that may be more critical to accuracy.

I believe that the condition and consistency of the inside of the neck of the case is FAR more important than seating depth personally. I haven't seen anything super drastic (and proven repeatable) from seating depth, but I've absolutely seen it from inconsistent necks and neck tension.

 

[Phil Rizzo]

Run them clean or dirty inside, lubed or brushed, just make sure they are all the same…and an arbor press with a gauge/indicator allows you to cull the occasional oddball.

 

[cajun]

https://precisionrifleblog.com/2020/04/05/bullet-jump-load-development-data/

https://precisionrifleblog.com/2020/03/21/bullet-jump-and-seating-depth-reloading-best-practices/

If you want to nerd out. If it's true that seating depth doesn't matter then a lot of really good shooters have been really wrong for a long time. The truth is you cant shoot 30 rounds for every small change you'll burn out your throat before you find a load. I'm not sure what the real " truth" is.

 

[Doghunter23]

https://precisionrifleblog.com/2020/04/05/bullet-jump-load-development-data/

https://precisionrifleblog.com/2020/03/21/bullet-jump-and-seating-depth-reloading-best-practices/

If you want to nerd out. If it's true that seating depth doesn't matter then a lot of really good shooters have been really wrong for a long time. The truth is you cant shoot 30 rounds for every small change you'll burn out your throat before you find a load. I'm not sure what the real " truth" is.

I have read these articles and agree with what they found. Also different bullet styles have different responses to seating depth. Like flat base respond much differently to seating depth than say hammers do. I have found very little variation in precision shooting them. I can get better precision with say a cup and core flat base at close range but can't run the same velocity. If they are basically saying that every bullet style is different and hybrid bullets were designed to be very forgiving over a wider range of seating depths. Then I say of course they were designed that way!

 

[Veteran]

I am new (since 2019) to the long range shooting community and admittedly my experience is limited. I have been frustrated with all the voices claiming their methods are "how it should be done". I am not inferring that their methods don't work, what I am saying is that if so many different methods all produce the same results, accurate loads, then logically not all of the processes in the various methods are as significant as believed. In other words, the methods may work, but not for the reasons we believe. My goal is, through applying the scientific method, to sort out what actually makes a difference in the reloading process and what is just the deeply held dogma of the community.

I deeply appreciate and respect the experience and knowledge of those in this community, and their willingness to share it. I know that their methods work and produce accurate results, all I am trying to do is figure out why. After recently stumbling across the following information, I have radically changed my thoughts on how I approach reloading. I thought the community might benefit from the information they proffer.

I am looking to have an honest discussion about the information linked below and to hear your opinions, many with infinitely more experience and knowledge than I. If you take the time to review either of them, I would welcome your insight, obviously your have been doing this a lot longer than I.

Rifle Nodes: How You’ve Been Wasting Your Time and Money on Load Development

Everything you know about rifle nodes and load development might be wrong. Click here to see the results for yourself.

www.outdoorlife.com

Bullet Seating Depth absolutely matters, and the reason it matters is because of rifle system harmonics. How deep you seat the bullet, has an effect on
bullet exit timing at the muzzle. Not just due to the micro effect in milli seconds from spacing the bullet further from the muzzle, but due to the interaction of the
ignition and combustion pressure in the chamber, burn rate of the powder,
and the difference in pressure and velocity and the pressure and velocity waves in the barrel, and the direction the muzzle is pointing at bullet exit, ie, rifle system harmonics.

I and many others have posted a lot of material about harmonics, and cited many white papers, and the web site of varmintal.com where you can drink from the firehose of science all you want. Varmint AL worked at Lawrence Livermore labs and modeled systems with FEA analysis. Finite element Analysis. He had a lot of fun in modeling rifle systems using these sophisiticated cell to cell models, to predict the effects of harmonics. There may even be a model on bullet seating depth on his web site? I don't recall. But, he certainly looked at different powders, varying barrel lengths and lots of other variables. Its all related and it all relates to the positon of the muzzle and where it is pointing at bullet exit mill-seconds timing.

I promise you, if you want to understand the science and the WHY bullet seating depth matters, and how it plays out scientifically in accuracy results, the answer is in rifle system harmonics and the physics related to bullet exit timing versus the position of the barrel for any given rifle at bullet exit time from the muzzle.

There is your answer, there is your mission, there is your field of study, and the results can be quantified scientifically with sophisticated FEA modeling, incorporating physics, chemistry, mathematics, harmonics, and then by actual empirical results on the target.

Go To! You have a lot of studying and homework to do.

 

[VenatusDominus]

Bullet Seating Depth absolutely matters, and the reason it matters is because of rifle system harmonics. How deep you seat the bullet, has an effect on
bullet exit timing at the muzzle. Not just due to the micro effect in milli seconds from spacing the bullet further from the muzzle, but due to the interaction of the
ignition and combustion pressure in the chamber, burn rate of the powder,
and the difference in pressure and velocity and the pressure and velocity waves in the barrel, and the direction the muzzle is pointing at bullet exit, ie, rifle system harmonics.

I and many others have posted a lot of material about harmonics, and cited many white papers, and the web site of varmintal.com where you can drink from the firehose of science all you want. Varmint AL worked at Lawrence Livermore labs and modeled systems with FEA analysis. Finite element Analysis. He had a lot of fun in modeling rifle systems using these sophisiticated cell to cell models, to predict the effects of harmonics. There may even be a model on bullet seating depth on his web site? I don't recall. But, he certainly looked at different powders, varying barrel lengths and lots of other variables. Its all related and it all relates to the positon of the muzzle and where it is pointing at bullet exit mill-seconds timing.

I promise you, if you want to understand the science and the WHY bullet seating depth matters, and how it plays out scientifically in accuracy results, the answer is in rifle system harmonics and the physics related to bullet exit timing versus the position of the barrel for any given rifle at bullet exit time from the muzzle.

There is your answer, there is your mission, there is your field of study, and the results can be quantified scientifically with sophisticated FEA modeling, incorporating physics, chemistry, mathematics, harmonics, and then by actual empirical results on the target.

Go To! You have a lot of studying and homework to do.

I absolutely agree the rifle system harmonics relative to exit timing of the projectile are what effect the accuracy (cone of dispersion) of the system. But I am also starting to believe that a few thousands of an inch change in the starting position of the projectile has a minimal effect on that timing relative to the massive effect of the conversion of potential energy to kinetic energy inside the case. IF you could make that energy conversion 100% consistent, then yes, by changing the starting position of the bullet you could change the timing of its exit. But given the relatively huge variation of that energy conversion compared to the relatively minute changes in starting position, I am no longer convinced it matters as much as I once believed.

 

[Veteran]

I absolutely agree the rifle system harmonics relative to exit timing of the projectile are what effect the accuracy (cone of dispersion) of the system. But I am also starting to believe that a few thousands of an inch change in the starting position of the projectile has a minimal effect on that timing relative to the massive effect of the conversion of potential energy to kinetic energy inside the case. IF you could make that energy conversion 100% consistent, then yes, by changing the starting position of the bullet you could change the timing of its exit. But given the relatively huge variation of that energy conversion compared to the relatively minute changes in starting position, I am no longer convinced it matters as much as I once believed.

Oh, I said as much in my post.
Just moving the bullet likely doesnt have proportionately the same impact on the bullet exit timing as does the impact on pressure and the combustion process in the chamber.

The burn rate of the powder is changed by that pressure and burn rate is a non linear equation.

You can end up with more or less pressure and velocity than you would predict in a linear equation because that explosion acts in a non linear fashion.

We all know burn rate is non linear from shooting RL 26 on a 105 degree day.......

So, yes, a small thousands here or there on seating especially if you are getting into or away from the lands can give you magnitudes more change than you might expect.

And yes, milli seconds here and there on exit timing is the whole game with respect to harmonics
and accuracy. Go do your homework. Go look at millisecond differences in the FEA modeling vs. on target accuracy.

And every rifle system is different, every bullet shape and weight is different. Every powder and powder bullet/ Burn rate interaction is different. All of the above vs. the distance to the lands, and compared to the fill capacity of the brass case being used is different.

Every last detail and how all of those details interact in any specific case are all going to matter but in different ways, all depending.......so you might find a case where seating doesnt matter as much maybe due to bullet shape and design like hammers. Other cases using big fat blunt nosed bullets, I guarantee you will matter more.

I'm gonna quote Dirty Harry......

A scientist wanna be has to know his limitations........

It all depends......in one design that is bullet driven, what matters most will differ from a different design case that is more explosion and combustion driven.

It all matters. Every detail.

 

[VenatusDominus]

Oh, I said as much in my post.
Just moving the bullet likely doesnt have proportionately the same impact on the bullet exit timing as does the impact on pressure and the combustion process in the chamber.

The burn rate of the powder is changed by that pressure and burn rate is a non linear equation.

You can end up with more or less pressure and velocity than you would predict in a linear equation because that explosion acts in a non linear fashion.

We all know burn rate is non linear from shooting RL 26 on a 105 degree day.......

So, yes, a small thousands here or there on seating especially if you are getting into or away from the lands can give you magnitudes more change than you might expect.

And yes, milli seconds here and there on exit timing is the whole game with respect to harmonics
and accuracy. Go do your homework. Go look at millisecond differences in the FEA modeling vs. on target accuracy.

And every rifle system is different, every bullet shape and weight is different. Every powder and powder bullet/ Burn rate interaction is different. All of the above vs. the distance to the lands, and compared to the fill capacity of the brass case being used is different.

Every last detail and how all of those details interact in any specific case are all going to matter but in different ways, all depending.......so you might find a case where seating doesnt matter as much maybe due to bullet shape and design like hammers. Other cases using big fat blunt nosed bullets, I guarantee you will matter more.

I'm gonna quote Dirty Harry......

A scientist wanna be has to know his limitations........

It all depends......in one design that is bullet driven, what matters most will differ from a different design case that is more explosion and combustion driven.

It all matters. Every detail.

Agreed, every detail matters. So...my previous method for working up a load for seating depth was a ladder starting at -0.020" (to stay out of the lands and possible carbon build up in the throat as the barrel fouls) and moving in -0.006" increments to -0.074". Shooting 3 shot groups and evaluating for group size. I know now that those 3 shot groups were nothing more than RANDOM points on the bell curve and not representative of any changes in seating depth. Shooting ten 3 shot groups at each seating depth to find the real effects of the seating depth changes is not practical from a cost/time/barrel life standpoint. How then are you quantifying the effects of your seating depth changes on accuracy?

 

[Veteran]

Agreed, every detail matters. So...my previous method for working up a load for seating depth was a ladder starting at -0.020" (to stay out of the lands and possible carbon build up in the throat as the barrel fouls) and moving in -0.006" increments to -0.074". Shooting 3 shot groups and evaluating for group size. I know now that those 3 shot groups were nothing more than RANDOM points on the bell curve and not representative of any changes in seating depth. Shooting ten 3 shot groups at each seating depth to find the real effects of the seating depth changes is not practical from a cost/time/barrel life standpoint. How then are you quantifying the effects of your seating depth changes on accuracy?

I dont follow. Are you saying you did not see any change in your groups from starting point to end point when you did this?

Seems like unless you are using a Berger hybrid or a Hammer bullet which can be relatively insensitive to bullet seating due to bullet design and shape, going from .02 to .074 off the lands you would have seen something, all other variables being held constant.

 

[RichCoyle]

What you could do is use a cartridge that does not erode the barrel very much. When I did my 2000 round test with a .223 it only moved the throat .021" (if I remember correctly) it was in the early 90s when I did it.

 

[VenatusDominus]

I dont follow. Are you saying you did not see any change in your groups from starting point to end point when you did this?

Seems like unless you are using a Berger hybrid or a Hammer bullet which can be relatively insensitive to bullet seating due to bullet design and shape, going from .02 to .074 off the lands you would have seen something, all other variables being held constant.

I did see changes. I detailed my results in post #102 on the previous page. I then took the best seating depth based on the 3 shot ladder and loaded 30 of them and posted the findings in #102. My ten 3 shot groups at -0.035" produced a combined group statistically identical to the combined 30 shots from the ladder test with three shots at ten different seating depths (-0.020" to -0.076"). I am shooting 147 ELDMs.