I think the real key to all this is understanding the real statistical variance of one's gun / shooting system. If you know that, you know what to expect.
As an example of figuring this out, when the conditions are ideal, I'll run a "benchmarking" benchrest test on my rigs. Below is the results of one I did where I took 80 shots at 80 bulls at 50 yards with my Air Ranger on a dead calm day at home. When I do this, I smooth out the surface of a duct seal trap and put the target paper directly on the duct seal - this gives me perfect holes and can measure the center of the shot in both the X and Y dimension relative to the POA (the center of the bull), and then I can do all sorts of wonderful statistical analysis in Excel.
The picture shows the plot of the full "80 shot group" both as shot, and slightly corrected so the COI (Center of Impact, or average POI) is dead on the POA, with scores and data for each. The worst shot of the 80 was only 10.7 mm off the POA, or 10.1 mm off after correction, so the gun is clearly very accurate and the conditions were clearly very calm. No hold off for wind was used - all shots were aimed dead on the bull. There were no called flyers, and the concentration this took for 80 shots was almost exhausting - that is why I stopped there instead of pushing through to 100.
I used a random number generator to pull "groups" of 5 and 10 shots out of the data, and then assessed them for min max and average. Based on ~10,000 5 shot groups and ~5,000 10 shot groups, I found the following:
| 5 shots | 10 shots |
Average group size (mm) = | 12.5 | 15.4 |
Minimum group size (mm) = | 2.4 | 5.9 |
Maximum group size (mm) = | 20.0 | 20.0 |
One thing I'll say is that people like to talk about "average group size" and I think that metric is just BS-ing ourselves as it mathematically scrubs out "outliers" that are not really outliers at all - they are just at the "bad end" of the normal operational range of the system. If one shoots five five shot groups, the average of the five does not mean much in terms of true system capability - a better question is to ask "how big the resulting 25 shot group would be" for those conditions, since that tells you what you really could expect to see if all does not go well, even if you do your absolute best. Infact, that should be what we use as our guns real "capability value" on any one given shot, as any one shot could fall in that larger window.
For that gun in those conditions, it basically said the gun could put the pellet within 11mm radially of the POA, so a potential max group of about 22mm seems likely – so call it an inch at 50 yards as the absolute worst case (since another 80 shots could yield one a bit farther out), but extremely unlikely. Of course that is in almost perfect conditions, benchrested taking great care on each shot, with the scope “perfectly” optically aligned so the COI matches the POA (which does not matter for “group size” anyways). Any shooting or sighting/range estimation errors will make it worse.
Anyways, that is the way I look at my shooting . . .
