To me, PRB & sidelocks go together like cookies and milk; it just fits.
Speaking of fit, rafsob is right on the money about ball/patch combos.
Additionally, though 90 may indeed be a good load for your Lyman you might consider starting lower, 65-70, work your way up incrementally noticing how this affects your grouping/accuracy.
As an aside, I just resolved grouping inconsistency on a new to me T/C Hawken by changing the ball/patch combo.
Good luck.