It's hard to know without seeing it in person, but GBBs are pretty simple so it shouldn't be too difficult to figure out where the issue is. You don't want to have so much oil in there that it is contaminating your hop up, but it definitely shouldn't be dry. Make sure your piston and nozzle are lubricated enough that the nozzle can easily slide over the piston o ring. You should also have a spring about 2 inches long that pushes the nozzle forward that sits in the top part of the blowback housing so make sure you have that. If you are unsure about how anything goes back together check out KnucklesGSM on youtube, he has a bunch of good videos on the TM design glocks that should help you get everything together properly.
