I have had better results using a slightly faster powder than either H 1000 or Retumbo when shooting the lighter bullets. These powders have worked better for me when shooting 160 grain bullets in the 7mm RM and 180 - 200 grin bullets in the .300 WM. Something closer to IMR 4831 has done well with the lighter bullets. All of my shooting with both of these cartridges have been with 24" - 26" barrels.