Thread: 3 vs 5 shot groups

I think a whole lot of people fundamentally fail to understand the variability involved in shooting groups...

Interestingly enough the man himself posted this on Facebook a couple of days ago...

Quoted from Bryan Litz

One thing you learn when you shoot a lot of groups is the wide range of group sizes that are normal for a given rifle/ammo combo.

Many shooters seem to expect a gun to shoot basically the same group size all the time, but that's simply not how it works.

What we've seen over 100's of 5-shot groups from .223 thru .375 is that the standard deviation of 5-shot groups is about 30% of the average. Statistics tells us that 67% of groups will be between +/-1 SD of the average, and 95% of groups will be +/-2 SD's of the average.

So for example, if you're long term group average is 0.5 moa, then 67% of your groups will be between .35 and .65 moa. Likewise, 95% (19/20) groups will be between .2 and .8 moa. Anything in that range is completely normal for a .5 average.

Originally Posted by ebf

I think a whole lot of people fundamentally fail to understand the variability involved in shooting groups...

Interestingly enough the man himself posted this on Facebook a couple of days ago...

Quoted from Bryan Litz

One thing you learn when you shoot a lot of groups is the wide range of group sizes that are normal for a given rifle/ammo combo.

Many shooters seem to expect a gun to shoot basically the same group size all the time, but that's simply not how it works.

What we've seen over 100's of 5-shot groups from .223 thru .375 is that the standard deviation of 5-shot groups is about 30% of the average. Statistics tells us that 67% of groups will be between +/-1 SD of the average, and 95% of groups will be +/-2 SD's of the average.

So for example, if you're long term group average is 0.5 moa, then 67% of your groups will be between .35 and .65 moa. Likewise, 95% (19/20) groups will be between .2 and .8 moa. Anything in that range is completely normal for a .5 average.

Well said to you both. This exposes the sheer folly of selecting a load based on one three shot group.
Regards Grandpamac.