Hi Karamoja,
I have not worked on one of their singleshots but I did buy and clean up one of their over/under double rifles in 30-06 caliber. I wanted to scope sight it for deer hunting and when I went to sight it in, I found that even decent groups with it were impossible because of the trigger pulls on the gun. I used my trigger pull gauge to check it each time I corrected something. It started out with triggers on it that pulled more than the gun weighed! I found that all the wood was too high on it and that the trigger mechanism was a mass of burrs and unpolished surfaces. It too, had a bunch of travel before breaking and lots of rough creepiness to the trigger pulls.
If you do the work yourself you will need photos of the action, which I see that you have already. Then you need to take the whole thing apart and de-burr all of it. Follow that up by stoning all mating surfaces that move and then polish them as best you can. I have some square stones for stoning but I do the polishing with 400 to 600 grit paper backed by a piece of steel.
The biggest part of the problem was the burrs but it also has a huge bearing surface where the sear release hits the sears. That will have to be shorted somewhat, BUT CAREFULLY! You don't want to take off too much metal or you will wind up with an unsafe gun! It would be best to consult a trained gunsmith and get his help and advice on this part. Keep polishing the surfaces till they really shine. That should help it alot, and do keep testing the pull as you go. This will mean assembling and dis-assembling the action several times. It is worth it in the end.
All these Russian guns close hard when new. I think it is because they are built on very tight tolerances, which actually surprised me. My over/under is still so tight that I have to almost pry it open. I'm fairly sure it will loosen up some with more use. I was pleasantly surprised at the quality of the machining and the accuracy after cleaning up the mechanism. They don't spend the time to smooth up the metal parts or get the wood down to a better fit the way others do. They are building basic utility guns at a cheap price. Good luck with your gun. Bob