Originally Posted by Bart B
That's news to me. Having worn out 3 or 4 match grade barrels in magnum cartridges getting no more than 1200 or so rounds producing sub 3/4 MOA accuracy at 1000 yards, they all performed the same from first shot to the end of barrel life. "Death throes" of each barrel lasted only a few dozen shots. First indication of nearing the end of barrel life was sight settings for a given load, range and altitude had to come up about 1 to 1.5 MOA due to throat erosion.
One's better off shooting one 90-shot group then do the math for ES/SD as well as mean shot radius. 'Course, if one doesn't belive tried and true statistics, then do something else.
Arsenals testing small arms ammo for all sorts of data shoot several dozen (a few hundred in some instances) shots per test group to get the best, most reliable data possible. Ever seen a 300-shot test group of 30 caliber ammo done at 600 yards?
3 shot groups, 5 shot groups, 90 shot groups don't matter.
There are ways to structure your testing to isolate different variables.
And, there are ways to statistically analyze whatever data you collect.
Regardless, the more good data you have, the higher confidence you can have in predicting future performance.
As to the OP, I get the feeling that most people eyeball the numbers and targets and just throw out numbers. I pay attention. But, it's just a reference point. I mostly focus on documenting my own performance so that I can tell whether I'm moving forwards or backwards because that's really all that I can control anyways.