i never under stood the 3 shot group therapy

[Dutchboy]

We are talking about two different things, here. Finding a load, and proving a load.

Three shot groups work just great to weed out "bad" loads. If you shoot three shots, and it's a 1.5 MOA endeavor, it has been my experience that shooting two or seven more times rarely improves the group! If you are looking for MOA, and three shots gives you 2 moa, chances are slim (statistically) to none that you are on the tail of a hot load. Sure, once in a hundred groups, you make a bad call. However, when you are in the middle of an incremental work-up, you get to see the "nodes" pretty quickly, even with 3 shot groups. If the rifle is at all accurate, that is.

On the other hand, once you are dialed in to a "potential" load, things change in a hurry.

In the past, "the standard" was 10 shot groups. The current bench rest standard is an "aggregate", or the average of five, five shot groups. This is statistically a little more robust than the 10 shot group, as a single flier has less influence. FWIW, Dutch.