Are you having problems with your current hop up system? Sounds like the bbs are not affected by the hop up, thus causing the bbs to dive down. If this is so, chances are, the hop up bucking is misaligned with the barrel. Installing a new barrel can cause problems as the mistake of having the bucking aligned upside down on the barrel can cause very bad things to happen. Luckily, its an easy fix.
Are you sure your hop up bucking is not upside down? I had a problem with the bucking being upside down, and it caused massive down hop.
Let me know if you are experiencing this problem, or need any more help/information.
Also, make an intro post so we can get to know you. Thank you for posting with proper grammar and punctuation, as many new members forget to do so.