A while back a friend of mine came into a good number of ammo cans full of Lake City 7.62 M852 and M118 Match ammunition. This was quite a windfall since we both liked to shoot out 308's a bunch.
In several of our rifles the grouping with the M118 ammunition showed flashes of brilliance, but overall the grouping was not that great and there were flyers we couldn't explain.
I grouped the ammo by the lots indicated on the boxes, and then I opened the packages and sorted the cartridges by runout. The results were an eye opener, a large percentage had runout from .006" to .010" which is not good for precision work.
To test the effect, I made up some batches with differing amounts of runout. I marked them in a way so I knew what each batch was, but no one else did. I got my friend to shoot them from an accurate rifle, but I did not tell him what he was testing. My instructions were to hold as consistently as possible.
What happened was the bad runout cartridges shot elliptical groups, and they had nearly empty centers. Here's where I get to your two in, one out point. In an elliptical group of seven shots or more it's pretty easy for two holes to be close together, say at 8 o'clock on the ellipse. Now pick a lone hole near the 12 to 3 o'clock side. Suppose those were the only three shots fired. Voila! A two in, one out group.
