How Many Groups?

[denton]

How many groups do you need to shoot to find out the accuracy of a firearm with a given load? It depends on how precise you need the answer to be. I've run the math:

A single five-shot group will give you the answer within plus or minus 50%. That is, if you shoot a 1" group, the long term average for that firearm and load could actually be anywhere between .5" and 1.5".

Five five-shot groups will give you an answer within plus or minus 25%.

Ten five-shot groups will give you an answer within plus or minus 17%.

[Cal Sibley]

I rarely shoot more than 3 groups (5 shots each) from any single firearm during a session. When I get home and dig out the calipers to measure my groups from the day I'll note which shot best. Next trip to the range I'll repeat that load again. If it fires well 3 trips in a row, I'll mark it as an accurate load and continue to shoot it. This gives me a good handle on repeatability of my loads. Just one mans method, but it works well for me. Best wishes.

Cal - Montreal

[denton]

Cal, that's a pretty good method. In order to cut the error in half, you have to do 4 times as many groups. Three groups are not a bad estimate.

[Cal Sibley]

Hello Denton,

It seems simple enough to me. I wasn't a math whiz in university.
I could probably compute the mean, median and mode and even whip up some standard deviations, but I suspect the only one really benefitting would be the store that sold me all those damn bullets. Best wishes.

Cal - Montreal

[Slim-Zippy]

I've got a little different system. I shoot three five shot groups, but instead of just measuring group size I measure the horizontal and vertical extremes. I believe that this gives me a better idea of hunting accuracy. I know that I am shooting into an average area.

Just my way of doing things,some shooters find it interesting.

John