Velocity Spreads?

Discussion in 'Reloading' started by ovastafford, Dec 13, 2009.

  1. ovastafford

    ovastafford Well-Known Member

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    I was wondering for long range shooting out to 1,000 yards what is the largest amount of velocity spread between shots? I have a really accurate load for my 300 but I was going to chronograph it.
    gun)
     
  2. J E Custom

    J E Custom Well-Known Member

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    If you have a good chronograph look for single digit SDs and if you can't get that low
    up to 15 SDs will work but the higher you go the shorter the range for acceptable
    accuracy.

    At shorter ranges the low SDs are not as important but at 1000 + yards it is very important.

    To get an idea look on a good ballistic chart that goes to 1000 + yards and use 2 velocities
    25 ft/sec apart and you will see the difference in drop and wind effect that 25 ft/sec has
    and cut it in half and that is the biggest number you would want.

    My best performing 1000 yard + rifles have had a SD of 3 or 4. but this does not come easy
    careful loading is a must.

    This is just my opinion and some may dissagree

    J E CUSTOM
     

  3. MontanaRifleman

    MontanaRifleman Well-Known Member

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    I take chrony readings with a big grain of salt. I bought a chrony alpha this year and shot it back to back with an old prochrony and they varied anywhere from 5-50 fps. I put more stock in the actual verticle spreads on the targets. Chronies can be helpful, but unless you have a really good one (and how would you know if you do?), I figure them for plus or minus 50 fps. I have seen one read exactley the same reading for the first two shots and then 50 fps different on the third.

    Mark
     
  4. ovastafford

    ovastafford Well-Known Member

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    So Im probably better off actually shooting at that range than relying on a chrony to tell me my load is accurate to that range correct?
     
  5. MontanaRifleman

    MontanaRifleman Well-Known Member

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    I would say that you can probably pick up trends from a chrony. I would hesitate to throw away or select a load on one outing over a chrony. If you shoot it on two or three different occasions under similar conditions and you are getting fairly consistant readings, then that's probably a reliable trend. If a cloud obscures the sun for part of your readings, they are likely to be off. This happens to me quite a lot.

    So the bottom line IMO is, where are the bullets hitting?
     
  6. Mikecr

    Mikecr Well-Known Member

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    Take care with your personal definition of 'accuracy' as well.
    For instance, you imply your load as accurate, but is it accurate at range(needed range)?
    Is your load accurate,, or consistent?
    Is it accurate under the conditions needed(like cold barrel, hot temps, off a bipod, etc)?

    The only correlation I'm aware of between accuracy and consistency, amounts to how consistent my accuracy is(hope that makes sense). My accuracy is taken to field potential, single shots.
    So I might count on 1/2moa of cold clean barrel accuracy, to 600yds, off a bipod, with a click card, within 70 to 100degs, using my Browing in 6br.
    But I wouldn't bet on it hot barrel grouping much better at 100yds.
    Doesn't matter. I kill woodchucks with it.

    I agree completely about cheap chronos. One thing I've concluded is that the single biggest improvement to ES/SD is a quality chronograph. I find that the ES people think they have is usally not actually that bad. And that's why they often shoot better than ballistics would predict.
    So I use an Oehler with 20ft screen spacing, and I spend a great deal of time using it with cold barrel load development.
    If you can't get a good chrono, go with field performance(as mentioned).
    You know what ES you need with a quick ballistic check. And you know what really matters by field testing.
     
  7. ovastafford

    ovastafford Well-Known Member

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    Thanks for the help guys. I dont have a chrony and I could probably borrow one but I think I will just go out and start out at 500. Work my way out and see how accuracy/ consistency is. Hopefully to 1,000 if it groups well enough at the shorter distances. Then see how my cold barrel consistency is. And correct me if Im wrong but velocity spread is represented in vertical climb/drop?
     
  8. Topshot

    Topshot Well-Known Member

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    +1 On what Montana says.

    On my cheep Chrony, I was getting E.S. of about 40fps and did not think my load would be any good at 1000 yards. Anyway I gave it a try and the thing shot on the money with a very low veritcal spread. I was surprised and quite happy. Since shot it at 440 yards, 610 yards as well and all is good.
    So you never know until you give it a go.
     
  9. Mike6158

    Mike6158 Well-Known Member

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    One other thing to remember about statistical data- the number of samples is very important. 5 - 10 samples isn't really enough to calculate an accurate standard deviation reading (SD). The chrony will do it for 2 rounds but it's not a usable number.

    ES is a similar but different issue (easier to calculate) but I think I would rather shoot 50 and throw out the highest and lowest reading than shoot 10 and call it good. There are so many variables in reloading that it makes ES a tool but not THE tool. I agree that the target tells a better tale for ES than the chrony.
     
  10. Mikecr

    Mikecr Well-Known Member

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    Only in a very rough sense..
    Drop can be influenced your bullet BC variance.
    Your barrel could throw bullets any direction as it comes in and out of tune.
    Your load could put the barrel on that edge of tune.
    Your system inaccuracy is always there.
    Certainly worth shooting still, to see how good your load performs at range.

    I disagree with generalizations about the value of ES, or that a great deal of shooting is needed for statistical value. Long range shooting should not be seen as a game of probabilities. Your not playing odds here.
    To focus on your actual capability, rather than probability, you cannot deny ES.
    Every shot counts
     
  11. Mike6158

    Mike6158 Well-Known Member

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    Actually my statistical reference was about standard deviation. It doesn't matter if you are speaking of bad apples to good apples in a crate or velocity variations in your pet load, the calculation is a statistical calculation and more data points equals more robust output data. The people at Shooting Chrony recommend a minimum of 10 data points.

    From the Shooting Chrony Manual:

    There's a reason that their higher end chronographs are capable of larger shot strings.

    ES is different. My suggestion was that if you want to use ES then use it, however, how the gun shoots is a much better indicator than ES imho. Not saying it's not useful. But ES is an indicator of the variability of the load more than anything (not saying it's the only indicator but it's the primary indicator imho). How consistent is the powder burning in your rifle / barrel combination? How consistent is the batch of primers that you used? How well did you measure the powder? How consistently did you seat the bullet? How consistent is the neck tension? How consistent does the barrel remain as you foul it with more and more rounds? I imagine that I'm leaving a lot out.

    I don't see Long Range shooting as a game of probabilities. However there is a probability of success given a set of conditions. That's one of the reasons we reload and people build custom rifles and custom barrels. Decreasing statistical variability increases the odds of hitting where you aim.

    Anyway... I'm not going to beat this to death. I don't spend a lot of time looking at chrony data because it takes too much time to do it right (for me). I shoot paper and when things get right I get the satisfaction of seeing the results and I get the pleasure of watching the load come together.
     
  12. MontanaRifleman

    MontanaRifleman Well-Known Member

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  13. Boss Hoss

    Boss Hoss Well-Known Member

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    I shoot 1K competition and like to win so this is a VERY important number for me.

    Like to have 10fps or less but the max is 25fps with 2, 5 shot strings.
     
  14. Boss Hoss

    Boss Hoss Well-Known Member

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    If you compete at 1K you would be murdered over the long term with vertical dispersion. Most guys who shoot sporters do not even have the right equipment or technique to properly evaluate the “complete” accuracy potential of a particular firearm at 1K. Primarily due to the importance of being able to judge condition.. Anyone can get lucky for 3 shots but to do it in a 20 or 30 shot string is another matter altogether. Just my .02

    Always ask people when they tell me that a rifle shot a certain size 3 shot group at whatever range stating that they could “compete” with this rifle------OK when you do that 10 times in a row then you will have something.