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Question ave spread of pellet

Discussion in 'Anything Airgun Related' started by Kada82, Jun 4, 2014.

  1. Kada82

    Kada82 Busy Member

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    Hiya lad & ladies
    im looking for a bit of advice on getting average fps spread. I can get the average fps. Hopefuly someone will know what i mean
     
  2. Clubshot

    Clubshot Clubshot

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    Totally depends on Gun / Fill and Pellets

    Nothing gives the Same

    ChairGun does give some figures

    Nothing beats a day on the Range with a Chrono -

    BOB/R
     
  3. terry1001

    terry1001 Major Poster

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    If you're using a spreadshett to analyse the shot string you can use the various formulae which can give you the average, the maximum, minimum and the standard deviation which is a way of expressing the degree of variation in the values.
    If you have Chairgun Pro (current version) on a PC then if you look at Toolbox/statistics you can enter your shot string and then calculate the various numbers you want.
     
  4. Dunkman

    Dunkman Posting Addict

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    Avg fps spread doesn't really mean anything in real life as what matters is just the average FPS to determine muzzle energy and the difference between max and min velocity as a measure of consistency of each shot.

    However, if you REALLY wanted to measure the average spread you need to shoot 10 x 10 shot strings, work out the spread between min and max FPS for EACH 10 shot string, add them all up and divide by 10 to get the average spread - bit pointless really.
     
    Last edited: Jun 4, 2014
  5. mattyts

    mattyts Donator

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    For shot to shot FPS variation,add up the difference in FPS between shot 1 & 2, 2 & 3 etc then divide by number of results.

    For shot string FPS variation, do shot strings of pellets from your fill pressure until empty,repeat 10 times,take the highest and lowest value,find the difference,do the same for the other 9 strings then divide by 10.

    Don't know why you would want to though?
     
    Last edited: Jun 4, 2014
  6. Kada82

    Kada82 Busy Member

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    Im using a combro and that only gives fps/fpe. I just want to see the the average shot to shot average thats all
     
  7. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    I think some are having difficulty understanding exactly what you're after (myself included to an extent). As matty says, to calculate the mean ("average"), sum all your velocities and divide by the number of shots.

    For example, if you had the following 5 shot string:

    780
    781
    783
    782
    779

    Adding them together gives at total of 3905, dividing this by the number of shots (5 in this case) gives a mean velocity of 781ft/s.

    The easiest way to analyse shot strings IMO is to stick them all into an Excel / Google spreadsheet; then all manner of functions can be used to extract information from them. Contrary to what some others say knowing the mean velocity and energy can be useful; something can generally be learned from many facets of a shot string as well as the mean - such as extreme spread, standard deviation, maximum.... all easy to calculate with a spreadsheet ;)
     
  8. terry1001

    terry1001 Major Poster

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    In my opinion it's actually easier to use Chairgun Pro, once youve typed in your velocity figures a single click of the mouse gives you all the basic statistics and a graph so you don't have to understand how to use a spreadsheet.
    If I'm doing full strings I connect my combro to a laptop and save the data for analysis in a spreadsheet, I normally use the free Open Office on my laptop but it does require some experience of using formulae and knowledge of what the various functions actually do. Using the Chairgun function requires none of this and it is also free.
     
  9. Kada82

    Kada82 Busy Member

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    Yeah i dont think i was asking right sorry ill use chairgun.
    i did my 5 shot then ÷ 5 to get my ave fps. But couldnt think of a away to get the ave spread ?

    I:E A reviewer says ave fps is 775 and ave spread is as low as 6fps. Hope that sort of clears it up
     
  10. mattyts

    mattyts Donator

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    I don't really think that's worth knowing.

    Just stating your lowest shot to shot variation and highest,aswell as the highest and lowest overall.
     
  11. loki_79

    loki_79 Donator

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    Standard Deviation is probably the most useful measure of the variation within a sample shot string if you want to compare pellets. For reference, my best pellets have an SD of about 1 or 1.5 fps, and the worst are 3 or 4 fps.

    There is a fairly accessible explanation of what is meant by a standard deviation here: http://www.mathsisfun.com/data/standard-deviation.html. All it means in practice is that 68% of you shots will be within +/- 1 standard deviation, and 95% will be with +/- 2 standard deviations (assuming a normal distribution).

    You can calculate the mean and SD in excel or open office etc, using the functions AVERAGE() and STDEV().
     
  12. terry1001

    terry1001 Major Poster

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    It all depends on what you'tr looking to get from your shot string. If you do a complete string from max fill pressure down to the point where velocity has obviously dropped right off then that can show you a number of things without any maths, you can easily identify your sweet spot (for a pcp) and you can tell if you are likely to exceed the legal limit.
    To get any real benefit from all the work you've put in collecting the data you do need to do a bit more and this is where it helps to have some understanding of maths and, even better, statistics. It's helpful to know your average velocity but, with a pcp, you should only use the information relating to your normal operating pressure, ie within the sweet spot. This will help in calculating muzzle energy and trajectory (using Chairgun or similar). You can also find out how consistent your velocity is and, as loki_79 has said, the standard deviation is a good measure of this but there are other ways of looking at it. If you are able to do these calculations you can evaluate the differences between pellets or the effect of carrying out tuning work on the consistency of your gun.
    For many people this is just too much information and they prefer to determine these effects by shooting. Unfortunately shooting introduces more variables, including the shooter and weather effects unlike a mathematical approach which reduces the variables to the absolute minimum although it does mean spending time, pellets and air shooting over a chrono.
    For anyone wanting to get some information on their rifle/pellet combination Chairgun Pro is probably the simplest as all you have to do is enter the numbers and click Analyse, if you can use a spreadsheet then you will have more power available.
     

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