Standard Deviation

Discussion in 'Reloading' started by Tidus56, Oct 4, 2018.

  1. Tidus56

    Tidus56 Well-Known Member

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    I recently starting shooting 20 shot strings to gather info on my loads. I understand all the data but I am not positive what is considered good for SD. I know from stats classes the smaller the SD the better but what is considered good for a 20 shot spread? With FF 243 AI brass a 20 shot string fired over 5 minutes I had an SD of 11.5. Is that decent for FF brass? What would be considered a great SD for 20 shots after FF, but also realistic?
     
  2. Kbaker657

    Kbaker657 Well-Known Member

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    I don’t know the weight of your barrel but regardless your shots should slow down as your barrel warms. If you shot all 20 in 5 minutes you had 15 seconds per shot so with that considered that is a good SD. If it is a hunting rifle I feel the most realistic measurement is cooling a standard amount of time between shots to bring the rifle back to as close to cold bore as possible. Once I am happy with the load and sd/extreme spread I am getting I will then fire groups of 3 in succession. In my mind a hunting rifle needs two successive shots at the same point vertically at the desired effective range in order to have a cold bore and follow up shot that is as true as possible
     
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  3. Tidus56

    Tidus56 Well-Known Member

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    This rifle is a varmint rifle, I use it for blasting prairie dogs. I usually shoot it slower than 20 in 5 minutes but there were targets needed red misting .
     
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  4. jamiebolseth

    jamiebolseth Well-Known Member

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    11.5 is good for 20 shots. 5 would be great.
     
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  5. rfurman24

    rfurman24 Well-Known Member

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    You will find many will disagree with me but you are doing nothing other than wasting components and barrel life. I development my loads with long range ladders. The target shows me everything I need to know. If I have small vertical at long distance I'm done. I zero the rifle for the load and do any tweaking necessary and start shooting. If the sd sucks the target will show you. If you missed the load the target will show you on following shoots.
     
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  6. Trnelson

    Trnelson Well-Known Member

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    I won’t bust your chops too much. You have some data, how valuable the data is or isn’t is another conversation.
    I personally would place much more weight upon ten recorded cold bore shots, that is much more relevant to hunting situations. How often are you going to have an opportunity to take more than two shots in quick succession on a game animal???? In thirty years of big game hunting I’ve never fired a third shot.
    All of my hunting rifles are cold bore zeroed. I’ll share my process, use what you want to, if you want to. I track and log cold bore data from every time I take a rifle to the range. The magnetospeed goes on atmospherics are recorded and the first shot data is recorded. If the cold bore to cold bore to cold bore SD is more than 8-10fps with a new load I know I need to control more variables in my reloading process if I intend to utilize the rifle ethically beyond 600 yards, that is my self-imposed standard.
    I remove the magnetospeed and let the rifle cool completely to ambient temperature then fire a ‘group’ of three cold bore shots allowing the rifle to cool completely to ambient in between shots at at least 600 yards to see if the load validates in a predictable fashion. After I have zeroed the rifle to the cold bore POI at a given range, usually 200 yards, I will let it cool again to ambient and then fire a single three shot group to track IF there is any shift from the first shot to the third. Usually, the difference is within my ability to aim and place bullets.
     
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  7. Tidus56

    Tidus56 Well-Known Member

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    That’s good info, I will try that with my hunting rifles. The gun that was in use was a prairie dog gun so no need for me to let it cool between shots because it won’t be used that way. More than anything I was just curious what a good SD is. It appears single digits are great on 11-15 is okay. I will be out with my 28 Nosler in the next few weeks. I will see it’s SD based on your test. Sounds like a lot of waiting around tho lol. Fortunately the Lab Radar doesn’t need to be removed so I will just shoot another gun while I wait for it to cool.
     
  8. bob4

    bob4 Well-Known Member

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    I bring a battery operated Milwaukee fan. Cuts my waiting in half in the Florida summer. Quicker in cooler weather.
     
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  9. Trnelson

    Trnelson Well-Known Member

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    Yeah. It leaves plenty of opportunities to bring quite a bit of the arsenal along to the range
     
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