I fixed the extra play by making a ring out of really, really thin metal (0.2mm) and fastened it to the slide so that the barrel goes through it. It completely stopped moving sideways and is as sturdy as it can be. After that I noticed that the slide still moves quite alot and after measuring it I noticed that the front tabs that go into the rail on the frame are 0.2 mm wider that the slide rail at the back of the gun... that's why the slide has extra play from side to side. So I fixed that by applying some tape-like-plastic-thingy to the front part of the frame where the slide moves and now e