Recent studies have shown that at magnum velocities, plastic tipped bullets had down range performance issues. The plastic tip deforms due to the heat generated at the higher velocities. Many if not all bullet manufacturers either have addressed or are in the process of addressing this issue. Try a non plastic tipped bullet. If you like Noslers give a 130gr partition a try and see if it improves things. Those lighter bullets are usually shorter and thus will stabilize better or worse in a given barrel length and twist combination. Test, document, refine and test some more. You'll hit on a load that is what you are looking for.