I have both of those calibers mentioned Both are in bpolt action guns. I use the 308 for deer hunting. The 300 mag is what I call my " moose gun" in case I ever draw a permit here in Maine. Many people say that the 300 is too much for deer, but the 308 with 150 grain bullet shot through both shoulders of a deer at 140 yards. Is that too much? My 223 shot through both shoulders at 80 yards, (55 grain PSP)
Just as well be the 300 Mag shooting through it. Nice flat trajectory from the 300 Mag. A little flatter than the 308.

But......I think that you can' t have too many guns!