i believe that in the back position as if a barrel is installed and action closed it should cock. I just had one do the same. i took it apart and cleaned it but couldn't see anything out of place. Ressembeled it and seems ok.It also had a problem with the hammer spring. I took the hammer spring and pin from another and it cleared that up .Wouldn't reset the trigger and internal safety feature to stop hammer form hitting fireing pin if bumped. The first hammer spring and pin worked in the second OK so don't know what to think.