If I'm working up a load for use in a magazine, I will make it just fit in the mag. Then I work my powder load until I find the lowest SD/ES at the speed I'm looking for. If I'm building a load and I'm not worried about mag length, then I start .030" off the lands and find my powder charge with lowest SD/ES. After I have the powder charge I like then I tweak my seating depth to see where I get the best accuracy. Most of the time it's between .015" and .030" jump. Finally I will check my accuracy and precision at 500yds or more.
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Seating depth tests
- Thread starter Korhil78
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Mikecr
Well-Known Member
That's not full seating testing, so it could work, or it could be dead wrong.
Let's say that full seating testing would indicate 70thou off as best coarse seating. But you didn't do that testing and went through your powder testing at less than best seating(something pulled outta your butt).
Now if all you cared about was ES, and NOT grouping, then seating isn't going to affect that. But if you were trying to tune your powder load for best grouping -while at less than best seating, you may have wasted your time. Also, if you try to do any coarse seating adjustments from best powder load, to find best seating, that won't really work either. The seating adjustments from there would collapse your tune, masking what seating alone would be doing. So you'd likely never get to the 70thou best seating with that.
It's best to do full seating testing first, and/or with powder backed away from expected tune. Then go into powder testing with that best coarse seating. Then go back to fine seating for tightest group shaping.
To understand this you have to accept the perspective that seating is not tuning, and should be handled separately from tuning.
Seating is prerequisite to best/worst results -regardless of tune.
Don't believe me?
Take a great shooting load for what it is, noting muzzle velocity.
Coarsely adjust seating to open grouping results as much as you can. Tweak a kernel or two powder to restore original MV, and notice that it doesn't fix the results. In fact, no amount of powder can make up for bad seating results.
I have well built hunting gun that is solid 1/3moa at 300yds. Good little shooter.
I could screw with powder load to cause opening to maybe 1/2moa (with horrible load density). I'd have to change powders to get worse in tune.
Yet, bullet seating 20thou deeper, right now, would take the gun to ~3/4+.
I seen it and know from full seating testing.
If you think any amount of powder load change makes a difference there, you're very wrong. Powder won't even begin to touch that.
If I fully powder developed at that 20thou deeper than best, I might get down to 1/2moa, but never 1/3 (far harder to reach).
Let's say that full seating testing would indicate 70thou off as best coarse seating. But you didn't do that testing and went through your powder testing at less than best seating(something pulled outta your butt).
Now if all you cared about was ES, and NOT grouping, then seating isn't going to affect that. But if you were trying to tune your powder load for best grouping -while at less than best seating, you may have wasted your time. Also, if you try to do any coarse seating adjustments from best powder load, to find best seating, that won't really work either. The seating adjustments from there would collapse your tune, masking what seating alone would be doing. So you'd likely never get to the 70thou best seating with that.
It's best to do full seating testing first, and/or with powder backed away from expected tune. Then go into powder testing with that best coarse seating. Then go back to fine seating for tightest group shaping.
To understand this you have to accept the perspective that seating is not tuning, and should be handled separately from tuning.
Seating is prerequisite to best/worst results -regardless of tune.
Don't believe me?
Take a great shooting load for what it is, noting muzzle velocity.
Coarsely adjust seating to open grouping results as much as you can. Tweak a kernel or two powder to restore original MV, and notice that it doesn't fix the results. In fact, no amount of powder can make up for bad seating results.
I have well built hunting gun that is solid 1/3moa at 300yds. Good little shooter.
I could screw with powder load to cause opening to maybe 1/2moa (with horrible load density). I'd have to change powders to get worse in tune.
Yet, bullet seating 20thou deeper, right now, would take the gun to ~3/4+.
I seen it and know from full seating testing.
If you think any amount of powder load change makes a difference there, you're very wrong. Powder won't even begin to touch that.
If I fully powder developed at that 20thou deeper than best, I might get down to 1/2moa, but never 1/3 (far harder to reach).
dbyes
Member
My ES/SD changes with seating depth keeping the same powder load. So if I have a low ES/SD and change seating depth the( numbers) ES/SD change and so far I can have a .4 group and the numbers stink and a big group with little numbers. so this thread is really interesting to me so I can learn
Mikecr
Well-Known Member
I'm sure there is a reason for that other than seating adjustments in general. Perhaps a precarious tension or load density situation.
That best grouping isn't following lowest MV variances is nothing new.
It's why OCW testing alone rarely leads to best grouping potential. It only resolves most 'forgiving' loads.
MV will change somewhat due to seating depth but I think what Mikecr is saying is that it's not comparable to the amount of change in ES/SD that you will have when you do powder charge development. This could be due to primer or the low powder charge itself.
I did a seating depth test the other day with a lower end powder charge. I only went from .010-.050 because I didn't have a lot of time but the ES from .010-.050 was only 46 FPS for 15 shots in one rifle and 44 ES for 15 shots in another rifle. That's not much considering the amount you changed seating depth.
Try changing powder charge and see how much your ES is. So in relation, powder charge difference will change group size somewhat but not near as much as it changes ES.
I did a seating depth test the other day with a lower end powder charge. I only went from .010-.050 because I didn't have a lot of time but the ES from .010-.050 was only 46 FPS for 15 shots in one rifle and 44 ES for 15 shots in another rifle. That's not much considering the amount you changed seating depth.
Try changing powder charge and see how much your ES is. So in relation, powder charge difference will change group size somewhat but not near as much as it changes ES.
I'm familiar with the Berger seating depth test.I just assumed that you would have to develop a load based on some sort of ladder test for powder first. Otherwise where do you start. I work up a powder charge ladder at 20 off to find a node on the high end then do a seating ladder. Never heard of doing a seating test first.
Rhovee
Well-Known Member
- Joined
- Jun 29, 2017
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I see it all the time. Seating DOES effect ES/SD. Multiple different rifles/bullets/powders. Certain bullets have tendencies for jump. I start there. Then powder. Then if i have to, do seating depth test with .005 in to about .040 off max. I do mostly shoot Berger's.
Seating depth absolutely can and does effect vel and as its deviation which anyone can see over a chrono.
There is a balancing act of give and take between powder charge and bullet land relationship.
Do a quick search on the subject and its clearly documented by numerous experienced shooter of numerous precision rifle disciplines
There is a balancing act of give and take between powder charge and bullet land relationship.
Do a quick search on the subject and its clearly documented by numerous experienced shooter of numerous precision rifle disciplines
Mikecr
Well-Known Member
With a good powder node ES/SD doesn't run away while seating changes are representing only minor pressure changes. And unless coming into or off lands, or donuts, seating barely affects velocity.
BrentM
Well-Known Member
Seating depth changes the volume inside the case. Yes it can and does change velocity potential which means it changes pressure. Generally you have to be on the extreme side of things to see the changes OOOOORRRRR you are not in a velocity stabile node. Extreme is something jammed in the lands to .250 out (think factory ammo).
Most people, even today, still think 100 yard groups is meaningful for long range shooting. Shooting a OCW or other ladder and dialing the rifle to that range and tweaking seating depth to get that bughole is still popular. However, if you are not in velocity stabile node, or in between a node, you can easily see a ES/SD go to crap.
For those who tune by velocity stability and stay in the middle of the node, the seating depth tests usually have minimal to NO affect. Since we are on a hunting page my thoughts are this: at a minimum seat the bullet in the neck of the case 1 diameter width deep. This should give enough bearing surface to neck to ensure concentricity and consistency of tension. Seat somewhere between 10-50 thou off the lands, as long as it means criteria #1, and then test powder charge. If your mag is short for the freebore then seat to max COAL that'll run in the mag, test powder.
Ive been doing the Satterlee method for a while now and it always works for me. I have not yet had a velocity stabile node that didn't shoot well at distance, took no seating depth testing, and may even produce bugholes at the zero distance(50,100,200...your choice). Now my criteria accuracy may not be good enough for you. I am super happy with .5 moa off my bipod, prone, with a rear bag, in the field at 400-600. Once I feel I can print several .5 level groups at that range I'll take it to 750-1100 to confirm data.
Most people, even today, still think 100 yard groups is meaningful for long range shooting. Shooting a OCW or other ladder and dialing the rifle to that range and tweaking seating depth to get that bughole is still popular. However, if you are not in velocity stabile node, or in between a node, you can easily see a ES/SD go to crap.
For those who tune by velocity stability and stay in the middle of the node, the seating depth tests usually have minimal to NO affect. Since we are on a hunting page my thoughts are this: at a minimum seat the bullet in the neck of the case 1 diameter width deep. This should give enough bearing surface to neck to ensure concentricity and consistency of tension. Seat somewhere between 10-50 thou off the lands, as long as it means criteria #1, and then test powder charge. If your mag is short for the freebore then seat to max COAL that'll run in the mag, test powder.
Ive been doing the Satterlee method for a while now and it always works for me. I have not yet had a velocity stabile node that didn't shoot well at distance, took no seating depth testing, and may even produce bugholes at the zero distance(50,100,200...your choice). Now my criteria accuracy may not be good enough for you. I am super happy with .5 moa off my bipod, prone, with a rear bag, in the field at 400-600. Once I feel I can print several .5 level groups at that range I'll take it to 750-1100 to confirm data.
Lets make a few assumptions first. Lets assume a straight chamber and ammo load. Bullet is in perfect alignment with the bore. Lets assume a perfect load density of say 100%. Lets assume fuether that there is no velocity change with seat chanhe or that its adjusted for.
Now with that setup what do people think is the reason changing bullet ogive to land relationship effects POI consistency? What is it that the change is effecting. As even in **** near perfect BR chambers and ammo that have as close to perfect bore alignment to bullet we still are adjusting bullet seating effect group size.
If it was barrel bend modes low freq harmonics they would have to be erratic to do this and they tend to be quite consistent. Point being the bullet would exit at the same angle and thus group well.
So what is it we are effecting by making this relational change?
Now with that setup what do people think is the reason changing bullet ogive to land relationship effects POI consistency? What is it that the change is effecting. As even in **** near perfect BR chambers and ammo that have as close to perfect bore alignment to bullet we still are adjusting bullet seating effect group size.
If it was barrel bend modes low freq harmonics they would have to be erratic to do this and they tend to be quite consistent. Point being the bullet would exit at the same angle and thus group well.
So what is it we are effecting by making this relational change?
I believe seating depth relates to barrel harmonics or barrel timing if you will. This is why if you are in a large powder node you don't see a radical change in poi or velocity with seating depth changes. Think of it this way. At a given velocity the time it takes the bullet to travel down the barrel is x. If you move the bullet closer or further from the lands you change the timing of the bullets exit from the muzzle. A stable velocity node is actually a spot in the barrels vibration where it is at the top or the bottom of its travel and not moving up or down rapidly. This is why if you do a ladder test with incremental powder charges sometimes a lower charge weight will impact higher on the target. It is exiting the barrel at a higher point in the barrels travel.
Mikecr
Well-Known Member
My theory: Bullet coupling to bore. A quality of connection.
Analogy: Ping Pong balls coupling to the Powerball tube they're sucked into. Some rattle a bit before full entry, some slip straight in. On a micro scale, slowed way down, there would likely be measurable reasons for the difference.
But on OUR only scale, it seems chaos. This, much like the apparent chaos with primer swapping. And there are repeatable reasons for result differences there as well.
I'm not suggesting an alignment issue, nor a timing issue, These fail tests regarding seating results.
But instead, a condition of bullet SPEED at coupling. Affecting that coupling.
For example, a bullet hitting the lands slow may couple well, then with more run/speed couples worse,, then with a little further run/speed couples well again,, then faster still and back to worse, etc. Like it's in & out of harmonics.
True or not, this passes tests as far as seating being independent of load, having only a slightest affect to tuning, but being a huge potential issue to results.
Just like primers.
These are potential issues that we clear with testing adjustments.
Analogy: Ping Pong balls coupling to the Powerball tube they're sucked into. Some rattle a bit before full entry, some slip straight in. On a micro scale, slowed way down, there would likely be measurable reasons for the difference.
But on OUR only scale, it seems chaos. This, much like the apparent chaos with primer swapping. And there are repeatable reasons for result differences there as well.
I'm not suggesting an alignment issue, nor a timing issue, These fail tests regarding seating results.
But instead, a condition of bullet SPEED at coupling. Affecting that coupling.
For example, a bullet hitting the lands slow may couple well, then with more run/speed couples worse,, then with a little further run/speed couples well again,, then faster still and back to worse, etc. Like it's in & out of harmonics.
True or not, this passes tests as far as seating being independent of load, having only a slightest affect to tuning, but being a huge potential issue to results.
Just like primers.
These are potential issues that we clear with testing adjustments.
Yes that is my point or theory. Most all of us know the owc and optimum barrel time theories. The two theroies both support or are proofs in support of each other. There is also plenty of support for low freq harmonic or barrel bend modes but they tend to be gradual and smooth like the way groups tend to cloverleaf around a center. Many on here know these theories.
Normally a typical barrel of lengths we use have bullet exit in the 3rd and 4th pressure wave cycle. That pressure wave ideally for a wide node would be as close to breech when the bullet is exiting the muzzle.
In the same manner when the bullet is just leaving the case and in the process of fully engraving the bearing surface the powder kernels are becoming fully ignted etc. This is a critical and equally volatile period as it pertains to effects on burn rate/pressure curve. If the bore diameter is distorted during this initial phase of the powder burn and pressure curve it creates a frictional change that then effects those properties. Outside being in the middle of a node this can cause large effects for extremely small changes or variables. A thou or two of seating depth a variation in bullet OTB measurement. The time period of when that initial pressure wave returns to the breech can happen in this same critical period of powder ignition and bullet engraving. The other thing is large changes going from jump to into lands can effect barrel timing enough to possibly have bullet exit at pressure wave reaching or getting close to muzzle. This could either cause the load to exit the node or put it near the edge where changes in enviornmental factors could cause it to exit the node.
To me the ideal configuration would be to have the pressure wave (1st cycle return) away from the breech with the bullet in the first couple inches and again as far away from the muzzle during bullet exit time which would likely be 4th cycle. Pressure wave speed is for practical purposes consistent.
I subscribe to the conclusion of Chris Long and his paper as he was the first time I saw this put forth in such a way. I certainly hadn't thought of it. Me dumb trigger puller maybe a bit smarter than your average backwoods hunter. I recall when he was still working on it and had initially released it. I sent many emails testing data points and theories. I had considered bullet alignment possibilities for seating depth effects. If this had been true there should not have been large changes from touching the lands thru to engraving at various depths. It should have gotten worse or better but not moved in and out and in for group size.
Considering this theory Chris put forth it fits as jumping vs engraved effects bullet progress per time differently. You also effect barrel exit time with seating changes. But this may not be an issue if you are in the middle of a node (which OWC can help find without data equipment ) you will still be in the node and a small adj in powder will get you back to middle.
I played with this so much I worked loads up using pressure trace using a cooler and heating pad to see how much barrel exit time changed relative to pressure wave. Point was if a person developed a load in middle of winter 30°F you might want to hedge the exit time with pressure wave so that both it and peak summertime heat 90°F would keep both loads equally from that collision point at the muzzle.
People can just do OCW or use quickload and a chrono to tweak it to use barrel exit time and need not worry about all the hows and whys. Tweak bullet seating however you wish to tighten groups. Its always a good idea to have the lowest SD/ES.
I can not help but jump down the rabbit holes as to the whys behind it all. One of the reasons I have ended up with the equivelent of a home ballistic lab.
Is this correct for its part of the puzzle? I think so. It has real world as well as scientific viable support. But who knows. As the variable of group size gets smaller for a given distance I think other areas such as barrel bend modes etc come in. If not then we would not see all those tuners attached and adjusted during BR matches which do not apply to our type of shooting
Normally a typical barrel of lengths we use have bullet exit in the 3rd and 4th pressure wave cycle. That pressure wave ideally for a wide node would be as close to breech when the bullet is exiting the muzzle.
In the same manner when the bullet is just leaving the case and in the process of fully engraving the bearing surface the powder kernels are becoming fully ignted etc. This is a critical and equally volatile period as it pertains to effects on burn rate/pressure curve. If the bore diameter is distorted during this initial phase of the powder burn and pressure curve it creates a frictional change that then effects those properties. Outside being in the middle of a node this can cause large effects for extremely small changes or variables. A thou or two of seating depth a variation in bullet OTB measurement. The time period of when that initial pressure wave returns to the breech can happen in this same critical period of powder ignition and bullet engraving. The other thing is large changes going from jump to into lands can effect barrel timing enough to possibly have bullet exit at pressure wave reaching or getting close to muzzle. This could either cause the load to exit the node or put it near the edge where changes in enviornmental factors could cause it to exit the node.
To me the ideal configuration would be to have the pressure wave (1st cycle return) away from the breech with the bullet in the first couple inches and again as far away from the muzzle during bullet exit time which would likely be 4th cycle. Pressure wave speed is for practical purposes consistent.
I subscribe to the conclusion of Chris Long and his paper as he was the first time I saw this put forth in such a way. I certainly hadn't thought of it. Me dumb trigger puller maybe a bit smarter than your average backwoods hunter. I recall when he was still working on it and had initially released it. I sent many emails testing data points and theories. I had considered bullet alignment possibilities for seating depth effects. If this had been true there should not have been large changes from touching the lands thru to engraving at various depths. It should have gotten worse or better but not moved in and out and in for group size.
Considering this theory Chris put forth it fits as jumping vs engraved effects bullet progress per time differently. You also effect barrel exit time with seating changes. But this may not be an issue if you are in the middle of a node (which OWC can help find without data equipment ) you will still be in the node and a small adj in powder will get you back to middle.
I played with this so much I worked loads up using pressure trace using a cooler and heating pad to see how much barrel exit time changed relative to pressure wave. Point was if a person developed a load in middle of winter 30°F you might want to hedge the exit time with pressure wave so that both it and peak summertime heat 90°F would keep both loads equally from that collision point at the muzzle.
People can just do OCW or use quickload and a chrono to tweak it to use barrel exit time and need not worry about all the hows and whys. Tweak bullet seating however you wish to tighten groups. Its always a good idea to have the lowest SD/ES.
I can not help but jump down the rabbit holes as to the whys behind it all. One of the reasons I have ended up with the equivelent of a home ballistic lab.
Is this correct for its part of the puzzle? I think so. It has real world as well as scientific viable support. But who knows. As the variable of group size gets smaller for a given distance I think other areas such as barrel bend modes etc come in. If not then we would not see all those tuners attached and adjusted during BR matches which do not apply to our type of shooting
