Question about SD, ES, and accuracy

Discussion in 'Reloading' started by BrentM, Oct 27, 2013.

  1. BrentM

    BrentM Well-Known Member

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    I have been chasing around a pressure issue and ran out after work Friday to test my newly reworked brass compared to some new brass and then out for a hunt.

    My thought was to try some loads in the reformed brass to see if I was still getting pressure and then back down the charge etc until the pressure signs went away.

    Long story short, the pressure was still there and the speeds high. All the pressure loads were over 3000. I backed down and played with 215 and 210 primers. What seemed to work was 56 grains and 210 primer. At .005 off the lands the pressure signs were mostly gone and the speeds:
    2978
    2981
    2974
    2983
    2972
    2972


    with 55.5 grains and 215 primer, .005
    2970
    2982
    2982
    2966

    None of this equated to a great group down range at 100. My hold sucked honestly and everything was under 1". I was rushing and not taking the time to shoot precision but really I wanted to try and reduce pressure to a level that seemed OK and start over.

    Does SD and ES have anything to do with tight groups? I am just being stubborn and worrying too much about velocity when I should just back it down to 2900 to 2950 and look for SD/ES and that give me an accuracy node? I want to get as much velocity as I can with decent accuracy (.5) or less but kind of wondering if I am going about it all wrong. I used to not worry about the chrono, shot the load until no pressure sign, found seating the gave accuracy, called it a day.
     
  2. Korhil78

    Korhil78 Well-Known Member

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    I have not used a chrono in a while actually. I will tell you how my load development went with my 338 LM.

    I loaded up the test loads, shot them and found the most accurate load out of them all. Went .5 gr above and below that load to see if I could squeeze more accuracy out. Took the most accurate out of those and played with the seating depth a little to see if I could tighten it up anymore. I was doing all of this out at 500 yards after the first initial testing though and on calm days.

    I loaded up my final load and zeroed it at 100 yards. I went out and verified my drops starting at 300 yards all the way back to a mile. Played with the velocity in shooter along with a few other tweeks in shooter to match my drops exactly. I dont know what my ES and SD is. Heck, I don't even know what my velocity from a chrono actually is. But man my gun is shooting some tight groups out at 1000 and beyond and I couldn't be happier.

    If your gun is shooting accurate out at long range and doing so consistently, I dont really believe that ES and SD matter a whole lot. Consistency of accuracy is my main thing that I worry about.

    You do need to make sure that you are not shooting at too high of a pressure though. That can mess with how consistent you are and the life of your brass. Find a node that isn't over pressured and stretch it out to see if it is consistent in the accuracy department. Remember that speed isnt everything. If you have a 2900-2950 fps load that shows no pressure and shoots consistently accurate, I would take that over a half way decent load that goes 3000 fps anyday.

    Your load being consistently accurate will do VOLUMES to boost your shooting confidence. And confidence is a big deal in this sport.

    I am shooting a 300 gr berger out of a 26" tube and to match my drops, shooter says that my velocity is 2810 fps. I am shooting 93gr of H1000. I dont get any ejector marks on my brass or any sign of pressure unless I shoot in temps 80 degrees or above so I am right on the edge of the pressure/no pressure area. I bet if I chrono'd my load it would be pretty close to the 2810 fps but I dont know.
     

  3. BrentM

    BrentM Well-Known Member

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    I never owned a chrono until recently and a buddy and I split one. I did notice a few things with it that helped me understand pressure and seating depth.

    I think I am being distracted by gizmos and loosing focus on fundamentals.
     
  4. boomtube

    boomtube Well-Known Member

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    "Does SD and ES have anything to do with tight groups?"

    Not directluy, no. Inside maybe 300-400 yards, you could have zero ES and SD with lousy accuracy or the reverse. BUT ... you can't have good long range accuracy if the velocity ES and SD are lousy.
     
  5. varmintH8R

    varmintH8R Well-Known Member

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    I tend to follow Korhil78's school of thought. Find something that works first and foremost. I use my chrono when I am testing for max just to get an idea where I am at (and to see if something is wonky).

    After that, I won't hook it up again until I have a load developed that I am happy with. I do this for two reasons. One, it is another datapoint to confirm drops, downrange energy, etc. Two, if something gets out of whack in the future I have a baseline to see if there is a major change in velocity.

    Basically, I use the chrony to analyze a good load, not as a predictor of one.
     
  6. Korhil78

    Korhil78 Well-Known Member

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    That sentence sums up everything. I should have just typed that.
     
  7. BrentM

    BrentM Well-Known Member

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    Thanks guys. Great info and it confirms my thinking. I have had good LR results and figured the low es etc didn't mean much at point blank range.
     
  8. Greyfox

    Greyfox Well-Known Member

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    I recently was developing a a load for a new 300WM intended for LR hunting. I optimized two loads, same components except different powders, H1000 and Retumbo. Due to the powder shortage I really wanted to use the H1000 and conserve my lot of Retumbo for my 6.5x284. Accuracy testing at 100-300 yards showed the group size of H1000 was suoerb with consistent groups in the .25MOA range. The Retumbo was running .5MOA average. I was pretty happy with H1000 until I got to my chronographing. Chrono testing of both loads on three separate days, using my Magnetsoeed and Oehler gave consistent readings of 2825FPS with an ES of 25-35FPS for the H1000 and 2902FPS with an ES of 8-12FPS for the Retumbo. While the H1000 clearly seemed to produce the best accuracy at shorter ranges, it did produce vertical stringing at 1000 yards about 12-15" in size. At 1000 yards the Retumbo maintained symmetrical groups that were very close to .5MOA, vertical stringing being half the H1000. Except for my bullet, 210 Hunting VLD, I tried adjusting the variables to bring the H1000 down in ES, but couldn't get there. Ended up settling on Retumbo. I think this is the kind of situation where a chronograph proves to be very useful.
     
  9. BrentM

    BrentM Well-Known Member

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    Another good point. Thanks Greyfox.

    The load posted above that shoots a lower ES and SD is only able to put 1moa on paper at 100 and 200. I took it to 200 last night with .010, .050, .090, .100, and .130. VLDs seem to shoot better at .100 in my rifle that is why I have the .100 in there. Nothing really came together though. I threw in my pet load for the 160 matrix and it only shot .5 MOA at 200. It had been shooting a solid .25 moa at 200 before so something is different. Could be throat errosion. .5 is not bad so I zeroed the 160's and loaded the remaining 12 bullets I had. Taking one of the boys out tonight to hunt deer.

    On another note, I ordered another 100 160 matrix bullets and if all else fails I will load up my remaining lot of retumbo with these and they will be my wolf ammo for the winter. Unfortunately they are only flying around 2700 fps so my max range is not as far as I would like (due to terminal velocity). I will have to look and see what the min FPS is on these. Berger says around 1800 for the 140 vld hunt.