RE: 300 yard accuracy?
A good trigger can make a big difference to be sure. You may have to resign yourself to the fact that either that rifle can't shoot better than that or it could be (not saying it is) you and that rifle can't shoot better than that. Just a possibility that has to be considered. I know I'm not as good a shot as my rifle is capable of.
One way to know would be to have a trusted friend that is a known good shot shoot it for you and see if they get the same results.