There is a publication by Harold Vaughn, called "Rifle Accuracy Facts", which deals with this. (among other things)  Primarily a discussion of vibration harmonics, and about finding the velocity at which the bullet exits the barrel at the extreme of one of the vibrations.   At this point, the actual movement of the barrel in vibration will be at a minimum.
     The suggested method of firing the groups is a good one, as it tends to eliminate factors which might change between the firing of ONE group and the NEXT.  This is a useful ploy in many experimental designs.   Gets away from effects of light, wind, weather, phase-of-the-moon, and whatever.
      The afore-mentioned Harold Vaughn is a genuine rocket scientist who set out the examine causes of inaccuracy in rifles.   The book is out of print and hard to find -- maybe interlibrary loan would be a good source.

CHRIS
RGChristensen

     The "ladder method" will give you useful information about bbl vibrations -- Vaughn's book thoroughly explains what is going on, not only with this topic, but discussions of rifle barrels moving around in the action threads (hard to believe, but demonstrable) and other things.   I admit that $100+ seems somewhat a stiff price.
CHRIS
RGChristensen

Yep been around a few of them folks shooting at 100yds. Often times they will come over to see what kind of contraption I am shooting over at 200. And they kindly ask me how does it shoot so I let them have a look see at my target through my spotting scope and typically you will here a holy crap and it helps to calm down their egos a tad. And on the other hand we have a top thousand yard jacketed competitor and one who shoots competitive tactical and then it is me who is saying holy crap. Two of the nicest fellows one could meet. And then there are some of the black rifle folks who have extracted brass flying towards your head while trying to shoot and could care less.

JLouis

Hard not to include Chis Long when looking at Dan Newberry.

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At three of my clubs, and others, shooting bottles
is probably one of the most "offensive" of targets to use.
Per club regulations.
Sorry about that Schuetzenmeister.

Around here people go onto Forest Service land and break bottles, old computer monitors, and even shoot up old washing machines. Plus cans and other trash - pick it up when they leave? Noooooo. Then they wonder why the FS wants to end all shooting in National Forests.