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Old December 1, 2012, 09:08 AM   #15
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
4runnerman, a 20-shot group is nothing more than four 5-shot ones fired one after the other. A 30-shot group's 50% more 5-shot groups fired one after the other.

If one shoots five 5-shot groups aiming at the same point a few inches away from group center with a separate paper in the same place over the target for each group, you'll have two things. One is a 25-shot composite of all shots fired. The other is five separate 5-shot groups.

Compare the size of the 25-shot one to each of the 5-shot ones. More often than not, the 25-shot composite group is larger than any single 5-shot one. Take your favorite .22 rimfire to a 100 yard range and shoot ten 5-shot groups, each on separate paper atop a backer that shows the composite. An inexpensive and excellent way to understand all of this.

This relates to a phone conversation I had in the early 1970's with a Lake City Army Ammo Plant's ballistic engineer regarding some issues with one lot of M118 7.62 NATO match ammo. He mentioned an incident with a new hire that was learning the ropes how their ammo was tested for accuracy. They had just shot a 200+ shot group with a lot or M118 match ammo at 600 yards from their machine rested test barrel. Looking at that near 10-inch diameter group, he commented: "Look at all those half inch or so 5-shot groups on that target!!" To which the newly hired engineer responded: "Yup, there's a couple dozen or more of them. Too bad they ain't all at the same place." He told me he did this to asses the new hire's knowledge of what constitutes accuracy and was pleased that kid knew all the right stuff. They had fired over forty 5-shot groups at that target. They were not all the same size. One of them may well have been 1/2 inch and another almost 10 inches. But that ammo would shoot about no worse than 1/2 MOA at 100 yards.
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