The Benefits Of A 100-Shot Group
BY Herschel Smith
6 years, 3 months ago
To see how illustrative a small sampling might be, I decided to fire 100 rounds of the same ammo, out of the same rifle, during identical shooting and atmospheric conditions. My thinking was 100 carefully fired and recorded shots should provide a more practical picture of performance. The results changed the way I look at performance testing results, and might explain some of the misses we sometimes experience.
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If we accept this 100-shot accuracy test as being representative, it’s clear simply firing and chronographing a couple three- or five-shot groups is not illustrative of how any rifle/load combination will perform over time. If you want to know what you can really expect from your rifle, every time you pull the trigger on a certain load, you need to evaluate more than one box of ammo.
In this article he deals only with those pseudo-random variables like velocity due to differences in loading, bullet weight, etc. While it is well beyond the scope of this post, there are also things like stochastic vibration propagation along grain boundaries and crystalline structures of the gun barrel, which gets very complicated. That subject cannot be given justice here.
When you fire a 3-shot group and claim that the gun shoots “__” MOA, or a 5-shot group and that the gun is capable of “__” MOA, that’s only marginally useful. That data doesn’t meet the Central Limit Theorem (CLT) for convergence and presence of at least three moments (a mean, fractional standard deviation of < 5% and a Variance of the Variance that is acceptable to an analyst).
But 3-shot and 5-shot groups is all you’ll ever see from a gun manufacturer. Just realize that this is essentially meaningless and much more is needed to yield a standard distribution with proper variance.
On July 20, 2018 at 2:21 am, Nosmo said:
Those of us who shoot competitively routinely (well, sort of…) perform these “large group tests.” The environment isn’t as well controlled because we don’t get to choose the weather or wind on match day, but if one reloads and pays particular attention to consistent component selection, or buys commercial ammo from the same manufacturing lot, that, at least, is repeatable.
One develops a reasonably detailed history over time, which is quite useful for tracking barrel life, a mandatory skill for serious competitors. I’d question the necessity for doing a lot of 100-round controlled-environment groups because, while providing very useful data, with some calibers 100 rounds is a significant portion of useful barrel life.
On July 20, 2018 at 3:11 pm, DAN III said:
Seems to me a 100 round accuracy test is overkill. Once I zero @ 100m I am easily at the combat effective zone at 0-200m.
When the SHTF, 200m and less will be the normal engagement range to domestic communists.
On July 20, 2018 at 6:22 pm, scott s. said:
How do you account for fouling, leading, etc in a 100 shot group?