Good advice here. Assuming that the rifle passes all of these checks (guard screws tight, per instructions above; bases, mounts tight; scope known good performer), if it still doesn't perform, I'd do a "poor man's" floating job just to check.
Put a piece of credit card under the front action ring, just aft of the recoil lug, tighten guard screws, front first, ensuring some downward pressure from barreled action against stock lug mortise (to ensure that the back of the recoil lug is bearing against stock). If there's a problem with the bedding, or simply if the rifle likes a free floating barrel, it will show up on your first couple of groups. If this tightens up the groups, then it's a simple matter to glass bed the rifle and free float the barrel permanently.
If this doesn't do it, I'd shop for a new rifle or barrel.
