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 | | From: | MarkL | | Subject: | Measuring groups/accuracy | | Date: | Sat, 22 Jan 2005 00:51:15 +0000 (UTC) |
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 | Is anyone aware of any research, or at least conclusions, regarding
different ways to measure bullet hole groups?
I know the convention is to shoot X number of Y shot groups, then
measure the extreme spread of each group and calculate the average.
However, I don't want to shoot more groups/shots than necessary, or
waste my time by shooting fewer than necessary. For example, if I can
be 90% confident that a 10% difference in group sizes is meaningfull by
shooting three groups, I'd rather do that than shoot 10 groups to be
95% confident. Heck, I might settle for 80% confidence.
I'm looking for answers to questions like this
1) How many shots are enough and how many groups are enough to be X%
confident that a given difference is meaningfull?
2) Is one 10 shot group better than two five shot groups?
3) If I measure the Average Group Radius (AGR) instead of the Extreme
Spread (ES), can I reduce the number of shots required to get a
statistically significant answer?
It seems likely that AGR is a better method than ES, but has anybody
actually tested it? Just because everybody has been using ES forever
doesn't mean it's the best method. One good reason to use ES is that
it's far easier to do than AGR, but I have a computer program that
makes AGR easy enough.
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| | From: | Bart B. | | Subject: | Re: Measuring groups/accuracy | | Date: | Mon, 24 Jan 2005 05:53:49 +0000 (UTC) |
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| Your questions; my answers......
“Is anyone aware of any research, or at least conclusions, regarding
different ways to measure bullet hole groups?”
Yes. Here’s a good one.
http://www.shootingsoftware.com/measure.htm
And here’s a neat software package you can use. Just scan your test
targets, mark the holes, then calculate!
http://rawilson.net/shareware/index.html#gsc
“How many shots are enough and how many groups are enough to be X%
confident that a given difference is meaningful?”
A statistician told me some years ago that a 15-shot group is about 80%
confidence; a 20-shot group is about 90%.
“Is one 10 shot group better than two five shot groups?”
Yes.
“If I measure the Average Group Radius (AGR) instead of the Extreme
Spread (ES), can I reduce the number of shots required to get a
statistically significant answer?”
I don’t think so.
“It seems likely that AGR is a better method than ES, but has anybody
actually tested it?”
Military arsenals have used mean radius (same thing) as their small
arms ammo standard for decades. It’s the best method. Mean/average
radius is typically about 1/3rd of the group size. Frankfort Arsenal
and Lake City Army Ammunition Plant tested 30 caliber ammo at 600 yards
with 200 to 300 shots per group. I’ve seen a few of their 6-inch to
11-inch (approx.) extreme spread groups for match grade ammo. These
groups have a mean radius of about 2 to 3.5 inches.
It’s important to have good shooting skills if your test groups are
expected to have credence. Remember the groups you shoot reflect the
accuracy of your rifle and its sights, the ammo and you.
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