Thread: Variables affecting precision

Of course wind shifts POI, however, in my experience and data, 3- or 5- shot groups shift poi quite a lot even in zero wind conditions. This makes sense. You're taking a 3 or 5 round sample from a larger population. If you believe otherwise, what is your theoretical explanation for why a 10 or 20 round group will (almost always) be larger in size than a 5 round group ? It's simple - you sample more of the population and hence the spread.


for example here is a 20 round (0.9 MOA) group at 100 metres.

Here is one of the 5 round groups that were shot on a target pinned in front, to generate the 20 round overlay. Note the average ("aggregate") group size was about .49MOA, smallest 0.34 largest 0.66. The load was totally random and un-tuned. Book max of 2206H in FL sized brass with no other prep, seating depth whatever the die was set at for another bullet. No testing.



It's clear from this and any number of other examples that overlaying including POI is not the same as the bench rest aggregate. Aggregate is an average size but disregards position, thus it describes the true precision poorly, and only functions as a "relative index".

When I say "discarded" - I mean loads discarded in the load tuning process. My current understanding based on the evidence I can find is that "load tuning" processes get you to a good load in spite of the process, rather than because of it.

The test of a load development process is not "does it allow me to get a good load" but "does it allow me to distinguish whether loads are actually different"

So far, I have been unable to determine any real precision difference between loads using the conventional tuning approaches with small group sizes, when tested with larger groups.

The apparent differences go away when you take a more valid sample. Which of course makes sense conceptually when you think about taking sub-samples from a larger population.

It's clear that in some cases seating depth (particularly large steps) and powder charge do affect precision, but it's not clear that the effect size is very large at all, detectable practically, or necessary to fiddle with to get a load that is practically functional for any use.


If you have evidence otherwise, please post it so we can all understand - evidence in the form of targets, because "show me don't tell me "