Justin is absolutely correct. One of the difficulties of comparing relatively small sample sizes of groups -- whether they are at 50 yards or 100 -- is that there's ammo variation that still occurs within a box of ammo (let alone in a brick) it becomes virtually impossible to compare apples to apples.
Each individual round can be considered unique. It may behave similarly to most of the other rounds in the box, but it can still be different in one or a combination of ways that make each one distinctive. Few rounds even from the same lot will be exactly identical in areas such as the weight and dimensions of individual components including bullet, casing and priming as well as bullet seating depth and concentricity. The result is that they behave as individuals when they are shot and this individual behavior becomes magnified as distance increases.
Once rounds in a group are shot they are gone, literally destroyed. They can't be tested again in a different barrel or at a different distance. It's impossible to compare apples to apples. Only with a considerable number of groups from a lot of ammo can statistically reliable comparisons be made.
However...
There's one situation where the same rounds can be compared fairly at two different distances. That's at a place like the Lapua testing facilities in Ohio or Arizona. There ten rounds are shot through the test tunnel and electronic sensors record the results at both 50 meters and 100. The sensors don't interfere with the rounds as they pass 50 meters and only record results. The same bullets that produced a group at 50 by electronic means continue down the tunnel to record a group result electronically at 100. No paper is used for targets.
Since the same ammo produces results at 50 and 100 meters, it's possible to compare apples to apples.
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