SD and Barrel Harmonics

E

ekp

Guest
I am about to use a chronograph for the first time to work up some loads for my rifles. I have used the ladder approach in the past and the modified ladder approach which compares the group to center of target and eliminating loads that are farther away from the center. Standard deviation of velocities and which load gives you the best harmonics of a barrel intuitively would seem to be not correlated. My question would be which load would you use the one with less SD or the one with the better harmonics and can you make a correlation?
 
What range are you using the ladder test for? I've done them a 1000 yards and have used the group that stayed together best and was not affected by the wind even though some of the groups were in a straight line they were affected more by the wind, but I was told that that was the load to us. I went with my thoughts and finished second for score out of over 100 shooters. The Chronograph can be used to tell you what velocity your gun is working at, so when you change lots of powder you can get back to where you were.

Joe Salt
 
Joe, excellent answer. I have a question. If he found a load that had exceptional ES, that was somewhere near the velocity that seemed to be the best for that barrel, as far as accuracy, would you think that a tuner could be adjusted to bring the node to the low ES load? Just a thought...
 
I am afraid that only 100 yds is available to me. I know that the range is limited but I did see a difference between loads to center to point of aim. I am assuming that the load closest to the center of point of aim is the sweet spot of harmonics. Now applying the chronograph I may find a difference in SD. After finding the sweet spot I was going to adjust group size with seating depth. I guess the question would be what role does the chronograph have in load development vs the ladder.
 
Boyd I'm seeing more and more guys using tuners at or range and once you get a good ES. of under 10fps I think playing with the tuner will help.I look for the bullets in the group to cluster two to three shots in one hole! thats at 1000. EKP yes I think you're doing the right thing by playing with the seating depth, I know at 1000 yards it has helped me get the vertical out of the group. Some guys say increase the powder to get the vertical out, I had a ES. of 6fps so thought I'd play with the seating depth and it worked. Like I've said before it would be easier to show you things in person than for me to put it all in writing.

Joe Salt
 
ekp said:
I am about to use a chronograph for the first time to work up some loads for my rifles. I have used the ladder approach in the past and the modified ladder approach which compares the group to center of target and eliminating loads that are farther away from the center. Standard deviation of velocities and which load gives you the best harmonics of a barrel intuitively would seem to be not correlated. My question would be which load would you use the one with less SD or the one with the better harmonics and can you make a correlation?
Click to expand...

This is probably a mistake, but I'm going to opine.

:)


IN MY OPINION, if one has to work up loads only at 100yds, then "SD" overrides anything "harmonic." (((I use ES but that's just me, I think SD is a crutch)))

IT IS MY OPINION that your statement above about "intuitively not correlated" is correct.

5 fps of velocity does equal near on an inch of vertical at 1000yds.

And (IMO) "harmonics" are used to OVERRIDE, or compensate for variations in velocity and are therefore yardage specific.

al
 
Alinwa I have never got my ES. under 5or6fps some say they have but I've never seen it in a print out on a chronograph! All I was trying to explain about the ladder test was if you have a load that is straight across with say half inch of vertical but has ten inches of wind, and another group has two or three inches of vertical with only one inch of wind and prints higher in the test, I can fix the vertical. So if you have a load that shoots in the wind I'm going to try and improve on that. Hate trying to read wind, not good when I do! Boyd thanks that means a lot coming from you.



Joe Salt
 
U all lost me at the last turn. :rolleyes: I am not familiar with ES maybe someone could enlighten me. I know that I am handicapped at 100 yds but I have to make it work for me. So that being said is Sd any use to me in load development. As it turns out the loads with the smallest Sd is the same load that seems to show me the best harmonics. I have found in life that conclusions I have made when uneducated in any endeavor I usually have to cast aside when I become more informed. So the information I have provided should be considered in that light.
 
Now we're just getting confused :)

Basically, "lissen to Joe!!!" You're getting advice from one of the great current shooters.

I'm agreeing with him altho it may not be evident because I'm not clear to everyone.

ES is Extreme Spread, it's SD without the math.

al
 
Al,
I'm pretty sure that you know better. If you subtract the lowest velocity of a string of shots, from the highest, you get the Extreme Spread (ES), the difference between the lowest measured value and the highest.

On the other hand, using all of the values, and plotting them on a line graph with number of shots that had a particular range of velocities along the left side, and those ranges of velocities on the bottom, your should get what is called a normal distribution, that can also be described as a bell shaped curve. The top of the curve is the value that has the greatest number of occurrences, or in a velocity test, shots. SD stands for Standard deviation, which basically tells you how bunched up the other data points are around the average value, otherwise known as the mean. With a low SD the curve is taller and skinnier, and with a large one it is shorter and wider. The problem is that the number does not do you much good because it is the extremes in velocity within a record group that determine how much vertical, that is attributable to differences in velocity, that you will have. For that reason, I thing in this application, ES is a more useful number. This does not invalidate the use of SD for other applications, where it is quite useful. Here is some links that explain what SD is, and how to calculate it. http://en.wikipedia.org/wiki/Standard_deviation
http://www.mathsisfun.com/data/standard-deviation-formulas.html

The real reason for any confusion is that chronographs will give both ES and SD for a string of shots, to shooters who, in many cases, have no idea what the numbers represent, because they are so fortunate as to never have had to sit through a semester of statistics.

Feel free to make corrections. It has been 45 years since I took statistics in the business department of OU.
 
If the goal is to obtain a ES of 3-5 fps...I am not even in the same country let alone the ballpark.
 
EKP, Boyd and al are into the number stuff like Charles E is I just use the smallest numbers I can get, then play with things till they look pretty on paper. I'm going to sit down sometime and try writing everything I've ever tried on paper. Think out of the box as they say,you never know what might work! I'll give you a couple more things to keep you going annealing, neck tension, polish inside of necks and molly inside necks for more uniformed seating depth. Good luck.

Joe Salt
 
I once had a short range bench rest friend help me develop a load, he had reloading stuff set up for the range and we loaded there as we shot. He would load one case and I would shoot he would add 1 or 2 tenths of a grain I don't remember which and I would shoot again. I held same point of aim for all shoots and the impacts went higher and higher on the target till there were about 3 that were the same and then they started going down the target. We averaged the top shots that had no vertical and that was the load. I imagine you guys do this or something like to find the high node or the low node, but it was new to me and I thought it worked fine.
 
That is the ladder method and is supposed to be conducted at at least 200yds. I do not have a range that goes out that far so I try to make due with 100 yds. The method I use uses a round robin firing sequence so as to eliminate fouling and heat as a variable. The load that comes the closest to the point of aim is supposed to be the best load for the rifle. Group size is then adjusted by seating depth. I try to follow this methodology but sometimes I fail and fall into looking for the best group.
 
Joe Salt said:
EKP, Boyd and al are into the number stuff like Charles E is I just use the smallest numbers I can get, then play with things till they look pretty on paper. I'm going to sit down sometime and try writing everything I've ever tried on paper. Think out of the box as they say,you never know what might work! I'll give you a couple more things to keep you going annealing, neck tension, polish inside of necks and molly inside necks for more uniformed seating depth. Good luck.

Joe Salt
Click to expand...

nope, not me...... as I've said over and over SD is a crutch. I count TWO velocities, High, and Low :) Sure, I look at what's in between, a little, just like I keep a running tally of groceries in my cart, or make sure my last fry gets some ketchup.... but figgering SD????

Never.

I understand SD

I understand statistics.

I understand the accountant that took two shots. One hit 6ft to the right, he dialed over and hit 6ft to the left, BINGO! and he went home happy.

I'm on your side Joe.

al
 
elp,

I was going to stay out of this because I figured that someone would address a incorrect assumption you have in your tuning. The group that hits closests to you point of aim or as you also put it, in the middle of the ladder test should be the best, is the furthest from the truth. What you will be setting yourself up for is remarkable amount of vertical when you least expect it. You want to work the highest and lowest points. See which of these gives the best ES and work from there. Stay out of the middle of the harmonic path....period.

Hovis
 
ekp said:
That is the ladder method and is supposed to be conducted at at least 200yds. I do not have a range that goes out that far so I try to make due with 100 yds. The method I use uses a round robin firing sequence so as to eliminate fouling and heat as a variable. The load that comes the closest to the point of aim is supposed to be the best load for the rifle. Group size is then adjusted by seating depth. I try to follow this methodology but sometimes I fail and fall into looking for the best group.
Click to expand...

What you are looking for in a ladder test is small groups from shots with a range of powder charges. It doesn't matter where the center of the group is. Some focus just on small vertical from the ladder test, but tuning also effects horizontal. Changing anything, including seating depth, after the ladder test means you may no longer be tuned.

Listen to Hovis, I think he just said essentially the same thing.

Cheers,
Keith
 
Hovis Isn't the Ladder test suppose to show you which load gives you as little vertical as possible, that is closes to the point of aim? What I'm saying, I have had groups that were close to the center with no vertical but they always spread out horizontally in the group. So this is no good for the shooting I do! So what I'm saying is I'd rather have a group that was not affected by the wind, the vertical can be dealt with by changing seating depth or other mean. I'm talking three inches of vertical at 1000!

Joe Salt
 
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