clean the rifle bore carefully verify the scope mounts are rock solid, swap to a different scope as a test, if none of that works look into re-bedding the rifle
remington actions are generally decent, accuracy will vary but you should get a 1"-2" 100 yard group with most commercial ammo.
a dirty bore will frequently produce less than bragging size groups, but modern rifles tend to be rather accurate,
cheaper quality, scopes and scope mounts can and do fail,rather regularly,
you might want to take the rifle to a gunsmith for his inspection, and obviously I don,t know how good a shot you are,
but off a decent rest a consistent 2" or hopefully smaller 100 yard group should be rather easy to duplicate,
I would not be overly concerned if the rifle keeps at least a 1.5" 3 shot hundred yard group, off a solid bench rest,
lots of guys obsess over sub 1" groups,consistently,
the 300 WSM has a good reputation for accuracy with the 165-180 grain ammo.
most of those same guys can,t hit a coke can at 100 yards on the first shot,
from a rapidly acquired field position if their lives depended on it!
if your rifle consistently punches holes in a 2" orange dot at 100 yards off the bench rest,
set the impact to hit a couple inches high at 100 yards and go kill game!
everyones a hero off the bench rest, Ive won a wallet full of money on several occasions betting guys I could knock a hole in a coke can, we set out , where I set two about 3 feet apart on some hill side, we set those cans at 150 yard and bet who can punch a hole in his faster, take as many shots as you care too, first exploded coke can wins the bet,
Id bet they could not hit that can from a sitting position, everyone does great off a bench rest, trot 150 yards sit and try to hit a coke can, thats a great deal more related to real world hunting than some bench rest target
and in 50 plus years Ive yet to have a deer or elk complain if the bullet impacted a 1" off the intended point on his vitals
http://www.shootingtimes.com/editori...t_020911/99102
http://garage.grumpysperformance.com/index.php?threads/new-rifles-disappointing-accuracy.14856/#post-83123
http://garage.grumpysperformance.com/index.php?threads/do-you-practice-shooting-from-field-positions.9380/#post-71169