Not sure if I can help but you may find looking at a parts list will help you identify the problem. I just found an exploded parts list/diagram by a google search. The rivets you refer to are pins which are usually hardened. There also appears to be some sort of bracket that could restrain the cocking lever. Are you certain you got the parts back together correctly? Sorry to ask but mistakes can happen, especially as your problem seems to have happened immediately after a rebuild.
Have a look at the diagram and see it the assembly is OK.
Cheers, Phil