Well, I have been hunting mule deer in northeastern Montana since 1986.
For the first 10 years I used a 6mm Remingotn with an 85 grain Sierra HPBT bullet at ranges from 35 feet to 300 yards. Obtained complete one-shot, one-kill success.
For the next 4 years I hunted them with a .25-06 Remington using 120 grain Sierra HPBT bullets from 65 yards to 425 yards. Obtained the same 100% success.
For the next 4 years I used a 7mm Remington Magnum with 168 grain Sierra HPBT bullets at ranges of 120 yards to 600 yards. And, once again had 100% success.
This year I am using the 7mm Remington Magnum...haven't seen anything with horns worth shooting, but have seen a lot of doe. Season ends on the 27th, so sometime before Thanksgiving I have to go get me two of them...