can't get in weapons research room (LEVEL 9b)

I think the part you mean is where you go past the firing range, up the stairs and into the observation room. In this room is a machine that, when you click on it, allows you to take control of a gun/camera in another room. When you are looking through the camera move it about and you'll see a walker and a stack of fuel drums stacked against a door. Press the fire button to bloww them up which in tern blows up the door.

Hope this enough, if not let me know.