If the gate is all the way down on your spreader and you're still getting more seed on than you want.... I would consider changing the size of the sprockets.   Either decrease the size of the drive sprocket, or increase the size of the driven sprocket.   Or a combination thereof.   Course.... if the sprockets are too difficult to get off due to rust and such.... I may choose to be satisfied with the higher seeding rate.   Reality and practicality often trump my idealistic wishes.   If you know what I mean.  


gordon