What caliper is this gun??? How many shots per grouping and how quick are you shooting? Is it warm where you are ? Did you check the stock mounting screws? Did you check to see if the barrel is touching the stock[ the old dollar bill slide trick!]. Are you resting the gun on your rest on the stock or the barrel ? Do you use a rear sand bag ?
How bad are the groups??? Are you sure you are looking thru the scope the same way,every shot?
It ,most of the time,is just one little thing,that will mess things up !!!!