What are BCG overdosed symptoms?

All of the above and to add it's a lot harder on your brass. cases are usually dinged up. recoil is more violent and you can feel the buffer bottoming out in the tube.
 
Bolt will outrun the magazine and crash into the body/shoulder of the next cartridge in line. Empty cases will get caught in the ejection port. Empty cases will get big dings along the body and fly lazily forward. Bolt may appear to not lock back on an empty magazine, especially if the mag spring is weak.