This project explains the differences between Bulgarian and Russian Cyrillic from a visual perspective. That refers to the shapes of the glyphs.
За българската кирилица и малките букви
2011 / проучване
The main differences consern the lower case letters. In Russian Cyrillic they are minimized versions of the capitals. In Bulgarian Cyrillic the shapes are more rounded and have extra ascenders and discenders, just like in Latin.
The complete project will be uploaded soon.