Chaos, think of zen.
"The sight does not shake. It is you who are shaking"
...
The reflector sight displays the light pipper in absolute postioning, therefore, which ever way you look at it, how bad your view angle is, just get the bogey inside the circle and the bullets will go there.
However, this absoluteness also produces the wierd illusion of gun sights shaking around in a strange manner. This is actually your head shaking around. Violent moves will cause vibrations to the pilot, and when his head shakes, it looks like the pipper is shaking around in a weird fashion.
It's normal Chaos.