Really 3 shot groups are totally appropriate if you are combining them in a running average. Let me give you an example: A deer hunter says he rarely shoots over 3 shots at deer so he decides that a 3 shot group is how he wants to evaluate his load under its intended purpose. What he should do is fire 10 or so 3 shot groups For a running average. Realisticaly he doesn't even have to do them on the same day or he can even clean his barrel in between strings (especially if that's the state of the rifles barrel when he sets out to hunt) and let it cool. This is load/system reliability and would be appropriate.
The example Mule Deer gave using 10 shots makes sense shooting varmints or in volume and was able to detect a problem using this method.
