It will be the locking bolts ... Art from The Thompson Centre Collectors Association has a good article...send me your email and I will forward a photocopy. For now there are two possible remedies
1. smack the trigger guard with the palm of you hand with some force. Those locking bolts have varying makeups as per the generations...ie look at the photocopy I will send you
2. Remove the forearm and hinge pin and squeeze really hard
As well check the serial number...pre195,000 or so TC changed the lockup to what is called easy open after 195,000... they previously offered a retro-fit but since S&W took over TC they halted the retrofit. Don't give up these are great shooting guns. And read Mike Belm's information on line he has a lot of really good advice for TC shooters.
