Both shoot a .30 caliber bullet. The only measurable difference between the two is velocity. Velocity matters for certain bullets to expand. I shoot Barnes Triple Shocks and I think the minimum velocity is around 180-2000 for full expansion. All this means is the 300WM will theoretically allow for a longer shot and still have the velocity for the bullet to perform. I like the 300WM as an elk round and it's served me well; ironically, I've never taken a shot at elk past 140 yards.
So don't shoot a bullet that needs high velocity to expand. There are plenty of them out there that are real elk killers in a 308 or 30-06. The 308 has been used for 1000 yd competition. It'll reach out there with the right bullets.
“In a time of deceit telling the truth is a revolutionary act.” ― George Orwell
It's not over when you lose. It's over when you quit.
