Source: http://worldoftanks.ru/ru/news/pc-browser/1/accuracy_9_6/

Since this is not on EU portal yet (would be marginally more useful to post this instead of another premium shop bundle), here’s the Russian server explanation for the accuracy change in 9.6.

Basically, the official reason for the nerf is that the tanks were too accurate (shooting too often to the center of aim circle) even when the AC was not fully aimed. Thus, the developers decided to separate the aim circle into 10 zones and each zone has a certain probability to have the shell land in it. This is how it looks in 9.5:

The broken lines represent the various sectors and the circle, designated by unbroken white line – 70 percent of shells fall into that circle. The red dots represent the shell impacts within aim circles, the amount used for this sample was 3000 shots. Now, there wasn an issue allegedly of the “snap shot” accuracy (shots without aiming), when people, who were not aiming properly just managed to hit even fast low-armored targets repeatedly. Therefore, WG had to nerf this. This is how the distribution compares from 9.5 to 9.6

In order to prevent the stuff above, the probability of hitting exactly the center (“bull’s eye”) was reduced from 16 percent to 10 percent, but the chance for the shell to fall into the adjacent zone to the bull’s eye increased by the same difference. This change will keep the accuracy for the accurate/fully aimed guns while reducing the accuracy of snap shots.

And this is how it looks in 9.6 – not aimed gun versus fully aimed gun: