I've never owned a rifle that 4" groups was the best it would do a 100yds. I've bought a lot of abused/shot out Remington 700's for the action and they would still shoot better than that. I would take the rifle down and start from scratch, starting with the mounting of the action in the stock. If a wood stock, make sure it's not soft and eaten up by cleaning solvents. Inlet the barrel channel so there's no chance the stock can be causing an uneven pressure on the barrel. Check the trigger pull and if adjustable, bring it down to no more than three pounds, but no less than two pounds for a hunting rifle. Try to find the recommended torque for the action you have and torque the screw, a little on each one at a time.
Now, take the scope and mounting base off. Bed the mounting base with Devcon but only torque the screws about 75% or recommended torque. After 24 hours cure, remove one screw at the time,clean the holes and screws good with something that will take the release agent and any oils off. Put a small drop of blue Loctite on the last two or three threads and torgue it to recommend torque. Mount the rings on the base and lap the rings until you get at least a 75% contact surface and make sure to index mark the tops and bottoms of rings so you can be sure you get them back on the same way each time. Place the scope in the rings and torque the screws to the recommended torque. After getting the scope back on, mount the action or whole gun in a vice or some way that it will not move around. Sight the scope and zero in on a cross mark about 25 yards away and slowly more the adjust the windage and elevation through most of their range while looking through the scope, make sure it's moving every click. Be sure to note you starting point on the turrents and bring it back to the orignal turrent setting, them make sure the rectical is centered back exactly where you started.
Next you do a deep clean of the barrel and if you have a high powered magnifier of some sort, look close at the crown. Make sure it's still nice and sharp all the way around.
If it's still shooting four inch groups after this, you have the worst shooting rifle I've ever seen. That, or you need to go back to basic shooting 101 .