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Do you need at least 10 shots to establish a valid group?

1K views 8 replies 7 participants last post by  davidsog 
#1 ·
I think my actual Google search term was "What's the significance of the three-shot group?" Within the first few search results was this post: http://www.bealeinnovations.com/stats-3shotgroup.pdf

Now, I admit that I'm not a statistician/mathematician/engineer; however, other than kind of losing me with his three dimensional graphs, everything else he wrote about actual shot distribution seemed to make sense. And, I agree with his grandpa - hitting what you're shooting at is the point.

So, with that in mind, I ran my most recent 10-shot targets back through the OnTarget app to display the mean radius circle (drawn using the average distance of all the shots from the center of the group) and the group extent box (created by drawing intersecting straight lines through the center of the most outlying shots).

The rifle is a PTR 91 GI Classic; the ammunition is MEN 16 7.62x51. Unless otherwise noted, all the targets were shot from a table rest with the iron sights.







When shooting this target I was sitting on a small block and resting the barrel on a rail.


When shooting this target I was standing and using the sling.




When shooting this target I was standing, but leaning over and resting my elbow on a shelf.
 
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#2 ·
In the Military where I learned the three shot group is a good number because anything more and you could get multiple bullets through the same hole. But three shot group is only used for zeroing in the firearm. Other than zeroing the three shot group doesn't mean anything. Just my thoughts and opinion, take it for what it is worth to you.
 
#3 ·
Just to make sure that there's no confusion: the "W" and "H" are the width and height of the group extent box; the "Mean" number is the radius (distance from the center to the edge) of the circle, not a MOA.
 
#5 ·
I think ten shot groups are important in assessing accuracy. A guy who goes by the username Molon on other forums who also posts albeit rarely to HKPro does a lot of great accuracy testing and he has written up a few interesting summaries of the reasons to use ten shots.

I hope this does not violate any rules by linking this but here is one series of posts explaining his logic:
The Texas Sharpshooter

Here is another:
The Trouble With 3-Shot Groups - AR15.COM
 
#7 ·
I guess it really depends on what you are trying to accomplish. Assuming that you are trying to "zero" your sights, 10 would not be necessary. I would add a few pointers though:

Before "counting" those three rounds, you would first want to "foul" the barrel by firing one or two shots as a shot out of a clean barrel can be different from the follow-on shots. Next, ensure that your target allows you to focus your aim on a small clear point, black dots or squares are great. Reason being, is that you want your actual point of aim to be consistent so that it does not become a negative factor in your test. (the dark soldier target that you used would not be a good choice). Next would be your position choice. Most would argue that you would want to use the most steady position available and prone would fit that bill, but I tend to try and go with a more everyday realistic position and off a range bench while sitting would be my go-to (for rifle). Finally, and most importantly, is that you need to learn to "call" your shots because your test needs to consist of three good ones and any "flyers" caused by your (human) error need to be thrown out (assuming again that you are trying to zero the sights and/or check the accuracy of your ammunition, barrel etc.). To call your shots effectively, you basically have to train yourself to know where your sights were at the exact moment that the round was fired. No person is really rock-steady and we all have some form of wobble (keep it small) but if you clearly have identified a shot as one that you screwed up and it's off to the left (for instance) you shouldn't count that as one of your three (or ten) for that matter. Again, only count your good called shots.

Hope this helps:)
 
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