@Heavyopp, a close look at the muzzle's crown with a magnifying glass or bore scope would also be something else to do. A bad crown will spread out a group like this. Good sharp, even edge all the way around the bore and rifling is what you are hoping to see. Look for burrs coming off the corners of the rifling, rolled edges, deformity from behind hit with the end of a cleaning rod, ect.
It also would not hurt to push a pellet through the barrel bore from the breech end with a cleaning rod to get a "feel" for the bore. You might discover a tight spot in the back or middle that us squeezing the pellets smaller than the bore's end and that would make big groups as well.