Ladder test then OAL ?

[gle3105]

I just started using ladder testing about a year ago. Then I started using the 10 round load method looking for the smallest deviation/ flat spot. Once found I worked with that area of powder charge.
So once found and happy with es/dev my question would be , for the same bullet and changing the oal wouldn’t the es/dev change again?
I‘m thinking it would change due internal case capacity and pressure.
Possible noticeable in smaller cases not so much in larger?
Over thinking it?

 

[RustyInBend]

Possibly over-thinking it ... shoot it and find out. I had the same question on three different 6.5-CM rifles all with different seating depths due to magazine length. I figured I'd just try the charge that gave me single-digit SD's (5.1-ish) and see what happened. Whether through incredible skill, divine providence, or blind ass luck ... they all shot single-digits with varying COAL's. Problem solved.

 

[D-4297]

Many over-think the whole SD/ES issue , thinking that it's the Holy Grail of accuracy . I have seen 200 - 18's shot with a SD of 24 , and that quickly taught me that chasing the SD number didn't get me to 200's or high X count . Many bullets have a seating depth that is nearly common in most rifles . For instance ; nearly every F-class shooter I know does exactly what you have done when developing a "new" powder load , but if they are shooting a Berger Jugg OTM or Target , they seat the bullet at .015 off , and go from there . Adjusting seating depth as a follow-up . I have seen my SD number get higher , which perplexed me , because my X-count got higher , too . Now , I don't worry about the SD number , but I do care about the X - count . Let the Target tell you . Numbers Lie . Targets don't .

 

[NorCalMikie]

Shoot for group. Best? Adjust the powder charge. Only then adjust the seating depth.
ES/SD ? What's that? Same with FPS. Never seen a target gripe about speed not being fast enough.
And try 5 shot groups. Won't waste as much ammo.
And make sure you only change ONE THING AT A TIME!! If you don't , you'll get dizzy from going around in circles.

 

[INTJ]

I generally run a powder ladder then a seating ladder. ES/SD are only rough indicators, it's group size that matters.

 

[6bra1k]

ladder it to log VELOCITY and check for possible ACCURACY NODES.
that means you need to log each shots location and velocity.
you need to know you have min wind conditions so you are evaluating shots not wind.
then go to a 3 shot test of what looks good, then 5 shot test. then start adjusting oal.

 

[RegionRat]

Just some food for thought.

With a "10 shot Satterle" method, can a sample of 1 for each step really tell us there is a "flat spot" or would that evaporate on the next try?

With one sample per charge, would we really see the SD/ES?... or how many shots would we invest in each charge level to establish a stat? Starts to sound like more questions than answers doesn't it?

That is not to say a single sweep isn't a useful starting point, it is to say that isn't an ending point nor is it a copy of the Audette Ladder method since the Audette method emphasized shot fall rather than velocity.

There is nothing wrong with taking a risk on getting the single charge sweep to show us the potential nodes based on shot fall, but there has been too much emphasis given to using a single sweep to look for velocity flat spots that may or may not exist... and even of they did exist they wouldn't be the priority over tuning for group size nodes which may not line up with the tightest SD/ES.

If you are going to try a charge sweep method, use the distance to leverage the results. This often means sacrificing the horizontal windage values by looking at only the vertical values. You would then take those nodes and either repeat the test for verification or take one or two of those nodes and focus your efforts on them with verification and seating depth refinements.

I will also add that the majority of seating depth sweeps I have run will actually reduce velocity with increased seating depth, which runs counter to the concepts that reduced case volume increases pressure/velocity. (The math models don't need to match those results to add their value. But let's not go down too many rabbit holes in one thread. We will leave math models alone for today.)

If you were also to run a single sweep for seating depth steps I would recommend the same philosophy, i.e., don't emphasize the speed but do emphasize the shot fall. It takes fine steps to see the optimal seating depth nodes so don't jump over them. What you are looking for is the same as the charge tests, the shot fall of several steps should display a node that is worth going back and investigating and most guns and bullets will show more than one node outside of the jam zone.

BTW, all of these methods, good and bad, get confusing results if any important part of the system is so out of balance that it overshadows the results of the variables being tested. If your shooting, the gun, the prep work, etc, are not up to the same levels, then you can't see the difference. Keep things in balance and perspective when setting goals.

By taking the most information from the ladders and selecting the best potential nodes, you usually end up burning less money and time to tune a gun/load. Too much emphasis on shortcuts and speed generally leaves more questions than answers with money spent and more required to get to your goal. YMMV

Good Luck!

Happy New Year!!!

 

[gle3105]

RegionRat , Now this is interesting. Counter intuitive.

”I will also add that the majority of seating depth sweeps I have run will actually reduce velocity with increased seating depth, which runs counter to the concepts that reduced case volume increases pressure/velocity.”

Reduced velocity but psi gain noticed?

 

[RegionRat]

RegionRat , Now this is interesting. Counter intuitive.

”I will also add that the majority of seating depth sweeps I have run will actually reduce velocity with increased seating depth, which runs counter to the concepts that reduced case volume increases pressure/velocity.”

Reduced velocity but psi gain noticed?

Not the kind of pressure change that challenges safety margins. Even jam on typical match rifles is only about a four or five KSI increase on the peak. The velocity is from an integration of the pressure over time, so the peak pressure and the area under the curve are not the same thing.

Keep in mind, we are talking about seating depth testing, which is very different than the problems encountered with topics like accidental or uncontrolled bullet set backs that do have a potential for a dangerous increase in pressure.

The terminology isn't standardized, so I will call something like a sweep from touching lands to 80 thousandths of jump in five mil steps (seventeen steps) a wide sweep. There are competing theories for what causes changes in group performance with changes in seating depth and I'm too lazy to write that much today.

It is true that you have to factor for increased pressure in the context of internal case volume for a given charge. Pressure and velocity are related, but are also dependent upon concepts that are an integral of time. Rather than turn this into a math class, how about I show a typical plot of a wide seating test instead.



That is what a 6 Dasher with Varget does as you seat the bullet deeper and deeper. The speed drops about 35 fps, it doesn't increase.

This kind of plot isn't unique to the Dasher or 6mm, lots of other guns and calibers do the same things, i.e., decrease velocity with seating depth. I don't fret if the Quckload or GRT doesn't model the behavior one way or the other. If and when I am worried about pressure, I break out the strain gage kit and get to work. YMMV

Happy New Year!!!

 

[wkdickinson]

If you want to do an interesting experiment, load 4 rounds for each of the 10 power charge increments. Then shoot a 1-shot OCW test. Follow it with a 3-shot test for each of the 10 increments. Plot the 1 shot test on a graph and see what you think it tells you. Then build a graph using box-plots that show all 3 shots for each increment. Then average the 3 shot groups and plot the averages. Now compare them and see if there is any correlation.

Personally, after having done that test a number of times I have stopped using OCW. I much prefer to let the target tell tell me which charge weight groups the best. Then once I develop a load with best charge weight I do the same for "jump".

Only after I've found that "best" combination will I use my chrono. Then I will usually shoot 25 rounds to establish a good average velocity to calculate sight setting from. I usually I also check the SD and ES of that 25 round group, but I am not too concerned about those numbers, if the load groups well.

 

[Dave M.]

Many over-think the whole SD/ES issue , thinking that it's the Holy Grail of accuracy . I have seen 200 - 18's shot with a SD of 24 , and that quickly taught me that chasing the SD number didn't get me to 200's or high X count . Many bullets have a seating depth that is nearly common in most rifles . For instance ; nearly every F-class shooter I know does exactly what you have done when developing a "new" powder load , but if they are shooting a Berger Jugg OTM or Target , they seat the bullet at .015 off , and go from there . Adjusting seating depth as a follow-up . I have seen my SD number get higher , which perplexed me , because my X-count got higher , too . Now , I don't worry about the SD number , but I do care about the X - count . Let the Target tell you . Numbers Lie . Targets don't .

Please clarify for the OP if you mean 0.015” off hard jam? Or 0.015” off the lands (ie jumping)? Big difference.
Dave

 

[D-4297]

Clarification : I referenced .015 in my previous post . I do not JAM anything . The measurement is .015 off of touch from the Leade . There are some TR Shooters who Jam bullets , but I'm not one of them , and I don't know to many TR shooters that do . Seating depth according to performance on target .

 

[mikecr]

To me, it doesn't makes sense to test powder with untested seating.
And I know that adjusting seating from a powder node will just collapse that node, masking my seating test.
So I run full seating testing, and I do primer swap testing, before powder development.

As far as some 10-shot shortcut? I have no faith in shortcuts.

 

[INTJ]

To me, it doesn't makes sense to test powder with untested seating.
And I know that adjusting seating from a powder node will just collapse that node, masking my seating test.
So I run full seating testing, and I do primer swap testing, before powder development.

As far as some 10-shot shortcut? I have no faith in shortcuts.

I started to say that isn't what I usually see in 1000 yd BR tuning, but I guess it more if a "it depends."

A very thorough way to tune is powder, seating, and powder again. That said, once I have settled on seating--which I can't do if I didn't have a very good powder node, I usually chase the lands and test powder to fine tune the day before the match. Most of the time the powder and seating I found initially will hold though the season.

There is an interrelationship between seating and powder charge and primer and neck tension. When one gets to far out of whack the other(s) have to be adjusted.