Canadian Airgun Forum

Hi, i make a string of then shoots withy gun and use a website to calculate the stadard deviation my problem i have no idee if my velocity is constant enough to be accurate for 10 meter shooting ...



The standard deviation is 3.9 fps
Its a string of 10 shoots

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Uramex peacemaker
2240 custom
2300 custom
Slavia 630
Daisy 853c
Crosman 422
Beeman p-17
TAU 7
2200 magnum

A stdev 0f 4 fps on a 10 shot string is good enough for 10m target shooting. What would also be useful to know is what is the extreme spread, ES, (max-min) over the same string. an ES of 10 fps is pretty good.
If this is a CO2 gun, then the stats will vary with the rate of fire - generally they get worse the faster you shoot. If you want to understand the statistics of the normal distribution, here is a link that explains it pretty well. https://www.mathsisfun.com/data/standar ... table.html
Basically, , 67% of the shots are expected to fall within 1 standard deviation of the mean, in your example between 531 and 539 fps (ES = 8 fps). Then 95 percent would fall within 2 stdevs, or 527 and 543 fps (ES=16 fps), 99.7% would be within 3 stdevs, or 523 and 547 fps. The "tails" tell us the chance of exceeding/not achieving the extremes, so in your case there is half of (100-99.7)% or 0.15% of exceeding 543 fps. Doesn't mean your gun can even achieve 540 fps, but them's the statistics. if you record a 100 shot string your stats would be more reliable.
HIH.

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Iacio, ergo sum

My extreme is 15.6 fps. For the shooting speed it slow enough my 12g co2 tank never come really cold, have to take a walk every 3 shoots to change target , more than 3 i cant count the score just get a big hole. I practice at 6 meter on the basement.

The poi start dropping after 65 shoots. I check in the midle and at 60 shoots the velocity stay in the test number.

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Uramex peacemaker
2240 custom
2300 custom
Slavia 630
Daisy 853c
Crosman 422
Beeman p-17
TAU 7
2200 magnum

I use these coefficients https://hardairmagazine.com/ballistic-coefficients/. I then use this calculator https://shooterscalculator.com/ to get my holdover or under for shooting depending on my first or second Zero. The following 2 pics are results based on my Fusion 2 converted to hpa at 950 psi (630 fps) and 1000 psi (660 fps). I can see, that at the 2 different velocity the hold under changes .05" at 10 yards. I placed the sight height at zero as I only wanted to demonstrate the ability to calculate changes in hold under at 10 yards based on the 2 velocities. The drag function of Ga is not available in this calculator but it has given me very accurate results compared to when in field, using G1.