TOZ-78
I'm surprised that given the amount of skill that must exist among the members of this forum, that no one has suggested making a proper target stock for the gun. An ergonomic stock will appropriate bedding allows for a better and more stable hold. It would get you more points than an adjustable trigger (unless the trigger pull is ridiculously heavy; which the pull on the TOZ-78 is not). A non-adjustable trigger doesn't come out of calibration very often (or ever). Take a look at a Feinwerkbau match rifle with a wooden stock. That design is pretty good if you want better accuracy. The triggers on the TOZ-78 light pattern rifles are fine just as they are. Next, you'll need better ammo, but I'm sure you know where to get that.