In the bullet/ammo world the unit of measure is always weight. No one walks into Walmart and says gimme a box of 1.3" 300PRC rounds. They would say 180 grain Barnes or whatever. The heavier bullet in any caliber will always be LONGER than the lighter bullet. I don't shoot solids out of my .300 PRC, but I would shoot the heaviest bullets you can find, verify they shoot accurately out of your gun. Wanting to shoot the lightest bullet out of your .300 PRC for elk seems counter intuitive, since the round was developed to shoot heavy bullets. You may have to develop your own load data depending on how light you want to go