MiG-29 gun, fuel tank question

Back in the day, it was claimed that early MiG-29 could not fire the 30mm cannon with the centreline drop tank fitted, because the tank blocked the cannon casing ejection port. AFAIK this was incorrect.

Whats the real deal with this?

Also can the tank be dropped, or is it fit and removed on the ground? What are the full and empty restrictions?