Can SD and ES be a shortcut for accuracy

Discussion in 'Reloading' started by CA48, Aug 6, 2010.

  1. CA48

    CA48 Well-Known Member

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    At the house I have about 100 yards to play with and a back stop, at where I shoot I have about 2500 yards to play with but its a little bit of a drive. what I'm getting at is for less intensive load development, (for now) because of time available is it safe to say the load with the lowest SD and ES will be the most accurate at longer ranges. I would not always think so but would like to hear everyone's input. Loading for a 338 EDGE AI 300 SMK's planning on starting at 90.0 gr of H-1000 and working my way up. I know i could shoot groups at 100yd but I would like to see how it groups further out, although it may do well at 100 this does not always mean the same for extended ranges, although I will check out groups at 100 also.
     
  2. J E Custom

    J E Custom Well-Known Member

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    All that a good SD and ES does is tell you that you have a good powder, primer,case and bullet
    weight combination. It may be accurate or not but if you have good accuracy to then you have
    found the load for long distance.

    In the process of working up a load the SDs and ES are what I start with when I get them down
    (Preferably below 10 SD) then I start altering seating depth to improve accuracy or change to
    another brand/type of bullet of the same weight to find out what the rifle likes.

    I found that by using this method it saved me many loads and much time to get to the load that
    I needed.

    J E CUSTOM
     

  3. Jumpalot

    Jumpalot Well-Known Member

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    I would not start at 90 grains. My old lot of H1000, I was good at 93 grains. With my new lot, I'm getting flattened primers and ejector marks at 89.5 grains.
     
  4. groper

    groper Well-Known Member

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    In short, you MUST have a good ES and SD as a prequirement to an accurate long range load. You MUST ALSO have good accuracy in terms of group size which may not have anything to do with ES or SD, but more likely barrel harmonics or bullet types and seating depths.

    The reason ES and SD is important, is huge vertical impact variation at long range due to the muzzle velocity differences.

    In your circumstance, you can still develop a good long range load at 100yds by shooting your groups at 100yds THRU a chronograph at the same time. If you see very tight groups (accuracy) and the chrono is giving you very low ES and SD numbers with the tight groups, youve found a load with great long range potential and then you can take it your long range shooting spot and test it there at distance.

    If you get good SD ES numbers but the accuracy is poor, then you need to keep trying different seating depths or powder/primer combinations before wasting your time and heading out to your long range spot.

    make sense?
     
    Last edited: Aug 7, 2010
  5. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    The only thing that I will add to this is that 100yrds does not always show the accuracy potential of a load. My hunting rifle shoots the same group at 100 as it does at 200, and almost holds the same group at 300. I think there are a lot of loads thrown out because they do not look good at 100yrds. When in fact they were very good loads.

    I still shoot at 100yrds, but not necessarily for group. I run through the chrono, and watch the target. If the load is big at 100 then I don't bother. But if it is close to 1" then I will try it at 200yrds before discarding it.

    Good luck,

    Steve
     
    Last edited: Aug 7, 2010
  6. CA48

    CA48 Well-Known Member

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    Alright thanks every one for a better understanding on the subject
     
  7. Sako7STW

    Sako7STW Well-Known Member

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    Humor a NUB. What is SD and ES? How do you calculate it?
     
  8. trebark

    trebark Well-Known Member

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    SD = standard deviation
    ES = extreme spread

    You find this by shooting threw a chronograph. For instance, you might load five rounds with a given powder load. You then shoot each round through a chronograph and record the velocities of each.

    Let's say you get the following velocities of 2890, 2895, 2900, 2905, 2910. This would give you an ES of 20 (2910-2890 = 20) and SD = 7.9 (can't tell you how to calculate SD, I just use Excel)

    Do you understand why it is important to have a low SD and ES?
     
  9. nheninge

    nheninge Well-Known Member

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    ES and SD are excellent for determining a loads potential. But.... there are literally hundreds of factors that determine accuracy at long range. Can you see multiple wind changes over your intended distance, can you input altitude, humidity, distance accurately (under stress), can you see the target though your optics, is temperature affecting your velocity, is your target moving, is there an updraft/downdraft......you get my drift...???

    100 yard sub MOA groups (with low ES and SD) are often "orgasmic"... but like real life, when you are done, they leave you asking for more....
     
  10. Sako7STW

    Sako7STW Well-Known Member

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    Thanks so much for that explanation. It does make since to me. I just dont know all the abbreviations and lingo. To me thats would be common sense. The more consistent the round the more consistent the shot should be. I know alot of people that are happy if they can hit a milk jug at a hundred yards 3 times and go hunting with that result. They then shoot box after box out hunting and cant understand why. Now I can tell them they have a High SD and maybe ES and walk off LOL.
     
  11. Good

    Good Well-Known Member

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    I feel that a low SD and single digit ES will be an accurate round at any distance provided everything else remains the same. As long as you don't have scope movement, a different hold on the gun, all seating depths are the same, etc., then that will be an accurate round. I'm not very experienced, but as far as I can tell, consistency equals accuracy.

    Of course there are always exceptions to this. There might be a bullet that just absolutely likes a particular velocity range. The ES might not be the lowest, but the bullet just likes that twist rate, velocity, and everything else that is in the package providing for an accurate load. It is very likely that this round might be more accurate than the round with single digit ES. My job is to find the most accurate round, whether that is the round with the lowest ES and SD or not.

    Right now, we're digging the 208 AMAX with 48.4g RL17 out of a pretty much stock Rem700 .308 topped with IOR Valdada glass. Last time out it shot 4 rounds at .8" at 200 meters. It shot really well at 750 and 800yds also. The local range is in meters but only goes to 500. There are 750 and 800yard targets set up further out though. But, most people are finding their nodes at 46.5ish grains with this round.
     
  12. garfield

    garfield Active Member

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    for you, good ES and SD, -10fps?

    or one digit?

    and your chrono. error of +/-5% (or?)?

    how you deal with it?

    proof tunel?

    2 chrono. back to back?

    thk you
     
  13. Good

    Good Well-Known Member

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    First, a disclaimer: these are my theories and I welcome opposing thoughts as I want to learn. I don't have much experience with any of this. I would think if you can get one digit ES, that would be good. However, I don't think there will be much difference between 7 and 9 or 6 and 10. I would think there would be a difference between 7 and 30 though, but at what distance? Everything may look the same at 100 or even 200 or 300, but what about 1000yds? Someone here a while back had their ES at 7 with a 338 something or another. I don't know if I'll ever be able to achieve that with 30-06, .308, or 6.5x284, but it's a goal anyway.

    As for chrono, I wouldn't think it would really matter as long as all load testing was done with the same one. I guess it would be useful to check results with another chrono- maybe the two closest loads.

    All this = my own theory. I have no proof or evidence so take it for what it's worth, only my theory and i am not a ballestician or anything of the sort. I will say though, in that last example of the exception, once you find the velocity range the bullet likes, if then you get the ES and SD as low as possible within that range, that round will also be more accurate than just picking a round within the range with a higher ES, logically speaking and of course, IMHO...:D
     
  14. bedrok

    bedrok Well-Known Member

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    In my humble opinion, SD is relatively unimportant, but ES is everything. Partly because I'm too dumb to do the SD equation, and thereby understand it, but mostly because long range hunting is all about the first shot. How do you know the round you have chambered for that once in a lifetime 900 yd. shot isn't the "extreme" one of the group?