Crono data

[crovello]

I just bought a chrono and took some loads to the range today. In the past I would head to the range when someone I knew was there with a chrono and just check my average velocity. Now that I can take my time I see how much info you can get from a chrono. I was not sure what kind of extreme spread and standard deviation was acceptalbe.

I had some loads with VV N340 in both 40S&W and 45ACP

I was getting extreme spreads of up to 80 fps

And standard deviations of up to 30fps

Is this unacceptable?

I also had loads with Hodgdon Titegroup in 40S&W

This gave my extreme spreads of 36fps

And standard deviations of only 11fps

Is this more what I should be getting?

I also took some factory loads, Federal Hydra-shoks 180gr JHP for 40S&W

They had an extreme spread of 34fps

And standard deviation of just under 12fps

Dave

[ErikW]

First, standard deviation is statistically and practically irrelevant. (Attention SD queens: Thppppttt!)

As for the extreme spread, you just have to ask yourself if you find the extremes acceptable. Would it be OK to go to a major match chrono with all the rounds measuring the low of your spread? If the low end is below Major, you could be in trouble. Would it be OK to shoot all the stages with all the rounds coming out at the high end of your spread? If the high end produces unmanageable recoil, you could be in trouble.

Eighty fps is too much for me, assuming I'm going for 950 fps. 910 fps is Minor and 990 fps is excessively hot.

[ricciardelli]

If all the bullets make holes where you want them, SD and ES don't mean diddly.

[.40AET]

I also had loads with Hodgdon Titegroup in 40S&W

This gave my extreme spreads of 36fps

And standard deviations of only 11fps

Is this more what I should be getting?

YES! You have a winner!

[benos]

Ronin Coleman (from PACT) once told me that Mean Absolute Deviation is actually a much more useful figure that Standard Deviation. Now why this is the case I can't remember. But I do also remember him saying that SD was included (in his chronos) because that began as the industry standard (probably from Ohler), so folks were used to seeing (and comparing) that figure.

be

[crovello]

Eric, good point. I would feel the need to load hot if I had to get my rounds tested to be sure to make major.

I was talking to someone about my question and he pointed out that I was using mixed casings. I did not even think of this. Next time I head to the range with my chrono I will make sure I have all the same brass.

Brian made mention of (mean absolute deviation). My chrono does not give me that reading. Is that much different than extreme spread?

I shoot mostly local matches and they do not test your ammo. The last time I had them tested was an AWARE match in NY. That was many years ago and I do not remember how many rounds they use to calculate your loads. Is there a standard number of rounds they use?

Dave