the most efficient rifle ever is the one that gets shot often and is well practiced with. pretty much anything from .257 through 460 will kill deer and elk reliably in the hands of a skilled marksman. I do have to agree on rounds like the 30-06, 300wm, 270win......just on ammo availability. loose a box of shells for a 300RUM in SE washington and you will have to drive to spokane for more, if it was a 30-06.......every gas station has em'.