Why do I, in both personal and professional life, use multiple ten round groups to determine the baseline precision of every gun? Because it works. I have been fortunate to work at organizations that place an exceedingly high emphasis on shooting skill with almost unlimited resources. Last year I fired a bit over 42,000 rifle rounds with every single one of them being scored/measured. That is not at all an unusual amount.
I didn't always believe it. I very much used to be in the "3 rounds tests the rifle, 5 rounds tests the shooter" camp. Then several years ago I started working somewhere that placed an unusually high emphasis on marksmanship and the standard rifle/carbine drills and tests were shot on 25m pistol bulls eye (B8's) from muzzle to 200 yards from all positions. Just about every drill or test was based around 10 round groups. You zeroed with 10 rounds, scored with at least ten rounds, and every morning you confirmed zero with at least one 10 round group for score. There were/are no "oppsies", no "flyers", no "pulled shots", no excuses. Failing a test or missing a single shot could be the end of your job.
The explanation of why they do that? Because the best shooters and couches in the world- NRA High Masters, USPSA GM's, top 3 gunners, guys like Bryan Litz, etc. told them that was the way to do it. And through a couple decades of experience has proven that it works.
Even still I had my doubts initially so after work one Friday I took a recce M4 (16in match AR15) and stacked multiple target on top of each other. Now I knew that gun consistently shot sub MOA for 3 rounds at 100 yards, but also knew that I couldn't gaurantee it could hit a 1 MOA target.
So I had one target as a backer that caught all rounds. I fired 5x three round groups at five fresh targets and one that caught all 15 rounds. Then I fired 3x five round groups at 3 fresh targets and one that caught all 15 rounds. And then I fired 2x ten round groups on the French targets. And I also had the backer that had all 50 shots on it.
The result-
3 round groups averaged just under 1 MOA, yet the target with all the 3 rounds groups in it was just under 2 MOA. Of course looking at the seperate targets it was plain to see that those "sub MOA" 3 round groups had a nasty habit of not hitting the target in the same place.
The 5 round groups averaged something around 1.2-1.3 MOA, with the target that had all 15 rounds in it being right at 1.8 MOA. Hmmmm.
The two 10 round groups averaged almost exactly 2 MOA, with the target with both on it being around 2.1 MOA or so.
And then backer with all 50 shots had an extreme spread of 2.2 something MOA.
One of my teammates was good with statistics and did the math that a single 10 round group offered something in the high 80 to low 90% range of where all rounds fired will land. Three 10 round groups was in the high 90% range.
After we got electronic target systems I was able to do this many more times. Always the same results. Since following those standards I no longer have "off call" shots. I am much better able judge what shots are makable and which aren't, and have a solid grasp of the likelihood of hitting and know how to adjust the shot to make those numbers go up.
What does all that gibberish mean to the guys that just want to buy a rifle, zero and shoot animals? It depends. If all your doing is shooting deer at 100-200 yards than it really doesn't make a difference. The error present is a couple 3 round groups during zeroing is able to mask itself inside the target size. However, if you start trying to consistently kill game or targets past 200-300 yards than ALL of it matters. Those small inconsistencies and errors start adding up to lots of misses and low percentage odds.
It is nothing for those "half MOA 3 round" guys with hunting scopes, to have 3-4 MOA of error built in for that 400 yard shot at a deer. Things like true group size, a true zero, scope tracking, wind, etc. that do not cause issues at close range can and will screw up otherwise good shots.
As to the thought of 10 rounds groups having a human error to it.... I have to wonder at the people that believe they will be able to make shots in real life under stress/excitement whether it's hunting, self protection, or competition from often uncomfortable positions under time constraints, yet can't sit at a bench and press a trigger 10 times without have a seizure......
