RE: black powder pistol ?
I fixed a few of them for some guys in the club.
There is two ways you can go at it, you can also make the gun dangerous if you don't know any gunsmithing.
The problem is that the half cock sticks up so far that when the guns hammer releases from full cock to fire the half cock catches it, the way I fixed them was to machine the half cock deep enough into the part so the sear would miss it when the gun was fire. If you go to the trouble of doing this and the parts are soft steel,which most of these revolver replicas are and you want it to last a while case harden the hammer ,trigger and cylinder lock.
If you really want to shoot black powder pistol the best answer is a used black powder Rugar in good shape I pick one up once in a while and no other that I have seen will hold up or shoot like they do, I have hunted deer and boar with one with 35gr of powder and a conical ball [home made]. Lee