Hi,
Usually it is the mainspring or excessive headspace.
Your discription sounds like a mainspring problem.
If I am thinking of the same revolver, you have a coil mainspring assembly.
I "think" (famous last words) you can splice a j frame Smith spring into it.
It would be a gunsmith type operation because you would want to ensure that you had enough static mainspring weight to make the hammer strike the primmer hard enough for the primmers to fire.
Prior to all of this, take the grips off and look and the spring that is underneath. Is it rusty? Some of those guns rusted pretty bad and that caused firing problems. Try a little oil and see if that helps.