Thread: 3 shot groups are useless!

Originally Posted by Puffin

I've not felt the need to post further on this thread, what with Gimp holding the corner so well on his own. However, and perhaps surprisingly, I find that it is Greg's post that I keep coming back to as the one that is going to finally prompt me to hit the keyboard again, as being in need of some clarification in my view.

The general theme of the thread is about what constitutes statistical significance, and what statements on performance can fairly be made about a rifle from a given set of target data.

The conclusion that Greg’s two 6PPC benchrest rifles are both 0.1moa performers CANNOT be drawn from the targets he has posted. I hope that that is clear, because I didn’t think that the way it was presented, and in the context of the other posts, that it necessarily was?

Whereas other members have posted sets of targets and asked the question “what is the capability of this rifle when these targets are taken in isolation”, I wanted to point out that in Greg’s post the targets are not to be taken in isolation. He is drawing on a large amount of prior knowledge of his rifles that we are not being made privy to in making the statement that both these rifles are “genuine 0.1moa 5-shot rifles”.

He is in the very unusual position of having access to something of a performance benchmark in these two rifles and where groups that exceed a previously established baseline sizing can then reasonably be attributed to causes other than those relating to the rifles alone.

It becomes a demonstration that when we are approaching an assessment of a rifle from the opposite direction — where we have little knowledge of the rifle’s actual capability and are hoping to interpret a set of targets to draw our conclusions — that amongst other factors, the influence of the shooter and environment will be contributors to the group size and mean POI. While we of course accept this, such separation is rarely able to be demonstrated as it has been here.

It is interesting and I have also been thinking about it.

The question that arises is "what is meant by genuine 0.1moa 5-shot rifles ?"

The definition of that is rather important.

Is it -

- Rifles that will occasionally shoot a 0.1moa 5 shot group, as part of the natural variation in group sizes (but with an average group size larger than that)

OR

- Rifles that produce, on average, 0.1moa 5 shot groups (meaning that the natural variation results in both larger and smaller groups from time to time)

OR

- Rifles that can be characterised as having sufficient precision to produce a high hit probability on a 0.1MOA target (disregarding the other aspects of hit probability)


Of course, the rifle itself is not the entire picture, the shooter error is part of it.

what would be interesting would be to see the difference in average group size (or mean radius of all shots in those composite groups) between Greg vs, in his words - someone not an idiot driving them. (not having a go Greg !)


It is interesting to observe that an average 5 shot group size for a benchrest rifle being shot by an expert is over .25MOA. Makes the idea of .25MOA hunting rifles seem vanishingly unlikely in reality.

It would also be interesting to plot all shots and understand the overall actual precision - as the average of multiple groups is less informative than one single large group