Thread: 3 shot groups are useless!

I wouldn't say useless, however I'd say quite limited in what they can tell you, in many situations.

If you have a genuinely subMOA rifle and shooter system, as in, one that will put 20 or 30 rounds into a subMOA group (therefore if properly zeroed, can hit a submoa target excluding long range ballistic inputs), then a 3 round group will give you a reasonably good measure of your point of impact, within some margin of 1moa at the range you're shooting at.


The problem is that a single 3 round group or even a string of them and measuring the average size, cannot tell you the real dispersion of your system. 3 round groups or an average size of 3 round group is only a very small sample of the distribution of where shots from your barrel will disperse, and by the nature of this, most of the time a 3 round group will be "pretty good" relative to the actual dispersion. They also tend to leave us very open to calling things "fliers" and discounting them. You see this behaviour all the time. Look through recent load development threads.

Multiple 3 round groups do not reliably tell us anything more than a single, unless we actually understand the relative point of impact of all shots across those multiple 3 round groups.

I have seen it time and time again that 3 shot groups will give "wandering zero" where it's a rifle that has a true dispersion of maybe 2moa, but the 3 shot groups average less than 1moa - but don't give a good idea of where zero actually is. Most recently a tikka t3 7mm08 about a month ago - helped the owner set it up, he shot a 3 shot group at 100m, looked to be zeroed - took it out to 400m and it was weirdly low. Back to 100 and yes, the zero was actually low - the 3 shot group checking zero was just a lucky 3 from the upper end of the true dispersion.

Note that you don't have to shoot 10 round or 20 round groups to get accurate data. You just have to plot the relative point of impact of 10 or 20 shots, whether shot in a single group, or 20 days worth of 1 round at a fresh target.

As people have noted, the first round out of the barrel for the day is the important thing for hunting - yes, this is true, however

1. how many actually go out and shoot 1 round over and over again on different days to check that the one round hits where we want?
2. barrel heat is not the factor it is made out to be that prevents the shooting of larger groups. what is happening when you shoot a 5 or 10 round group and it gets larger is often NOT it "opening up" due to barrel heat - you're just getting a more complete sample of the distribution of shots from your barrel.


It is also largely irrelevant for hunting, as I've noted before. As hunters we shoot at large targets at close ranges, mainly. The limiting factor is generally shooter proficiency, by far, not the fact that they are shooting a 1.5moa rifle (that averages .75 3 shot groups, in a slightly different spot each time).

However the converse is also true - for hunting it's irrelevant to have a ".x MOA rifle" so maybe we should stop claiming that with inadequate data