Well, the czech ammo it pretty good, but, frankly, the ammo is not the problem with pie plate groups that close in. I would begin by checking the action screws. They may be loose. Tighten them up.
Next, I would look at the crown. If there is no rifling at the crown, some monkey overcleaned the gun, wearing out the crown. I would consider counterboring it.
If the crown is good and the screws are tight, I would try seeing if you need to shim the action. Sometimes the actions sit too low in the stock, and you need to raise it up to make it square. Research how to do this. It isn't hard.
If all of these things fail, perhaps you should look at yourself. Mosins are not the traditonal American rifle. They feel and handle differently. It could be that you just need to learn how to shoot your rifle. Try dry firing it a bit, maybe get a recoil pad, in case of flinching, and practice sighting it on immovable objects in the distance. The sights may be throwing you off. You may just need practice with it to learn the handling and use of the Mosin-Nagant. They are different.
Mauserguy