I bought one a few weeks ago and the hop-up was jammed all the way off, once I figured out how to open it all up and get to the hop-up I clicked the lever that the dial moves into place and now I have hop-up. Also if you over oil the gun then it sometimes loads two bb's/shoots a bb out the top/jams a bb in the slide causing it to spill all its gas. The over oiling problem I would imagine is on other guns also but this is my first GBB so I don't know.
Overall this is an amazing gun for $70.