What I mean is that my 3 shot groups are distinct because I only have 3 rounds at a particular charge weight of a certain powder behind a certain bullet at a certain seating depth. I hope for some consistency among those 3 shots, however outside factors and the precision of my ability to measure limits that. I do not necessarily expect similar performances with another 3 rounds with a different bullet, powder, charge, etc.
I also only load 3 rounds at a time, so I must break cheek weld and reload the rifle. Then I wait for a much greater time to fire the next 3 than the time I waited between those 3 shots. I feel quite confident that the groups are distinct, not just because I want them to be, but because of purposefully applied changes.
But, if I have 6 rounds of the same bullet, powder, and charge weight, when do I have 2 groups of 3 shots or one group of 6 if I load them all at once in the same rifle and fire them on the same day. When does a 3 shot group turn into a 2 shot plus a hanger on if wind or cloud cover changes end a group before intended?
One could shoot at the exact same target with all rounds and record impacts as they happen, so you don't necessarily need unique targets to separate groups. Since shooters are often looking for consistency, then they probably aren't using different types of ammunition when shooting multiple groups for that purpose. They're probably shooting many groups with the same rifle. Often at the same range. There's potentially a whole lot of similarities even with different groups, so when are you measuring a bunch of 5 shot groups versus measuring half as many 10 shot groups in a more time consuming manner.
That's basically why I started the thread, to ask how I definitively know I've shot two groups of 5 rounds to verify the load versus inadvertantly shooting one group of 10 in a messy way. Or if it's valid to overlay the two groups of 5 to compare to one 10 shot group, or maybe I could even mark the first 5 rounds on the target then shoot another 5 and expect it to be similar to shooting 10 rounds all at once.
And also why do people shoot larger or smaller groups. If we can always reasonably expect a higher round count to result in a bigger group, do we need to shoot higher rounds counts to verify that? Do we need to shoot smaller count groups to make sure they are tighter than a previous 10 shot?
I think I've got most of my answers, largely because I think there was more of a philosophical rather than statistical basis for my question now that I've gotten to thinking about it more.
