I've never ever looked for a one-hole group. That's a waste of my time. Such things only show up when one of two series of shooting stuff happens. One is when all the variables in rifle, ammunition, shooter and environment cancel each other out for every shot fired. The other is when all those variables are at zero. Which means, if you shoot enough shots with any rifle or ammo, one of the groups will be a one-holer; they're all capable of doing that. At least once.
How do you determine which one it was?
The largest groups shot with a given system (rifle + ammo + shooter) happen when all those variables add up. That tells you their cumulative amounts are large. So reduce them by doing the right things with the right stuff. Next time the largest group shot will be smaller. Do those things better and that biggest group's gonna be even smaller the next time.
Getting the average of several groups is almost as bad. Several few-shot groups' all-shots composite will, 99.9% of the time, be larger than the biggest few-shot group. And one series average could be smaller than another ones, but have the largest few shot groupo. As could the series having the biggest average have the smallest few-shot group.
Arsenals typically use mean radius of dozens of shots in a group testing rifle ammo. That shows the average distance a shot will go from group center. But the furthest shot is oft times 3 times as far away. A 300-shot group can have a mean radius at 600 yards of 3 inches. The average 10-shot group's about 6 inches The extreme spread of the group is 15 inches. But its got several few-shot groups well under 1 inch.
Go figure. . . . . . . Then use the method that gives the results you want.
Meanwhile shoot that 40.2 grain load several dozen times. One of the groups will be a tiny one-holer. The odds are in favor of that. So is the statistical probability.