[Slono]

Try setting your hop up to max, and clean your inner barrel and hop up rubber using your cleaning rod to rid the parts of any excess silicon oil. Mine leaked BBs because it was over lubricated in that area. Do whatever you can before sanding, because once you sand you can't reverse what you've done.

Also see if your nozzle sits all the way back on the blowback unit when you rack the slide. If its not settling all the way back what could be happening is that the "loading rod" is jamming into your hop up rubber causing the BBs to double chamber. If that's the case find out why its not sling shotting back into place.

Try the above things first to rule out any things that can be fixed without sanding.