Re: 300RUM is back from Rem. got ?s
There are many things that can be done with a rifle to improve it's accuracy potential.
Ensuring a good barreled action-to-stock fit is one that you're doing/planning.
Trigger work is another - beyond the mechanical work/doesn't work state your rifle experienced. A medium weight (personal preference here), crisp, consistent trigger pull is essential to achieve accuracy.
Also, squaring the bolt-face to the receiver lugs is another way to help achieve consistency (the primary goal to attain repeatable accuracy).
After these more reasonably priced upgrades, there is blue printing/receiver truing (essentially making sure the receiver is perfectly straight and makes perfectly straight and equal, concentric contact with the bolt and barrel), barrel replacement ( really spendy!!!), handloading your own ammunition, and much *more*.
Without knowing you, to get more out of your rifle a visit to a knowlegable/skilled gunsmith in your area may be in order.