+2 on needing a new gunsmith. I definitely sounds like the trigger/bolt spring. Rotating too far when being cocked pretty much eliminates the had spring as a culprit. Or, it could just be that the bolt is rusted/jammed/bound in the down position. Taking the trigger guard off and checking the trigger/bolt spring will tell the tale.
Fingers (Show Me MO smoke) McGee - AKA Man of Many Colts - Alter ego of Diabolical Ken; SASS Regulator 28564-L-TG; Rangemaster and stage writer extraordinaire; Frontiersman, Pistoleer, NRA Endowment Life, NMLRA, SAF, CCRKBA, STORM 327, SV115; Charter member, Central Ozarks Western Shooters
Cynic: A blackguard whose faulty vision see things as they are, not as they should be. Ambrose Bierce