Youre barrel and bullet combination will have a few "nodes" as you go up in charge weight where bullets will group better with barrel harmonies being right. You need to find the best one for your rifle.
You don't mention anything about seating depth. How far off the lands you are or how you achieve this. Consistensy here with give a better indication of group sizes with velocities. An OCW (Optimal charge weight) method will give you a structured way to test charge weight versus group size and a definite indicator as to what works best in your rifle. Search the internet for the above as to how to do it. Bullet seating depths are best done on a specific point on the ogive of the bullet. Hornady do a comparotor and the Shooting Shed does an improved version. OCW sheet will point you in the right direction as to charge weights once this is sorted then you can add subtract fractions to re check and then adjust seating depth for further possible improvements
Wapinchaw. I have an IOR 12x52x56 on one of my rifles. You are more than welcome to look through if you like. Good glass in the IOR. You know me from the clubs we have been and are in.