well, can you tell us what types of groups are you getting?
how are you HOLDING the rifle for testing?
it makes a difference(not saying you don;t know this, but I DON"T know you do either)

are groups stringing one way or another, or just all over the place??
do you have a different scope you can put on it to try?
have you looked really good at the bore, to see if there are any signs of damage? all the mro so at the exit of bore?

how do empty cases appear, any signs of stress?
how are you CLEANING the bore to star with?
HOW hot is the barrel when testing for groups?

is all the ammo your shooting the same or close to grain and bullet design?
any access to a chronograph to see what differences are in round to round?(don't laugh I have seen some factory loads be WAY off)

any chance of having someone else shoot a group or two? again, NOT bashing,. but some times this helps find problems, same can be said with Video-ing yourself shooting, to see if there is a form issue?
do you KNOW what rifling twist is in the barrel? that can some times help in finding better bullet selections!