Hi and welcome to the BBS and to the pistol (UBC), I had a problem with pellets jamming occasionally, I bought the pistol secondhand and thought it was due to wear or lack of maintenance, so I gave it a good clean and lube and so far I have not had any jams I have not tried to adjust mine so can not help you with that Not sure that I have helped you any but try spraying the mechanism with WD40 type lube.
Cheers Keith