Basically when you do a quick ads midair and release it before it can reduce the m_currentSpread to 0, then it do the normal ads spread to normal spread calculation but with the whole spread value. So for example with the grandier it increases the spread from 6 to around 40, which is impossible to get up to in normal circumstances.
Video of it in action. I included the m_currentSpread value in the top left.
The bug exist on all different weapon types.