I've seen the claim that MRP and RL-22 were near the same, or the same. MRP and 139 Scenars shoot one hole groups in my FN/Shilen 6.5x55. That combo beat out every other load I've tried.
Point being, don't limit MRP to 120's; it's slower than 4350 and one would think it would be as good if not better with heavier bullets.
DF
