The easiest way to have consistent hammerheads is to have the SAME throttle setting each and every time. And this throttle setting will not be idle! I usually give 3-4 clicks up throttle at the top of the line, wait until the plane slows to a stop, and then give full rudder. I also usually have elevator and aileron in - sometimes full aileron depending upon how long I wait to input rudder - torque rolling hammerheads suck! Once the plane starts to pivot, get off the throttle completely. The downline technique depends upon wind direction. If there is a strong cross-wind, apply a LITTLE opposite rudder before the pivot is complete, and hold it in to prevent the tail wag. Slowly release the rudder as you come down. If you have any rolling elements on the downline, make sure you are completely out of the rudder before rolling, or the roll will look terrible. If there is no cross-wind (yeah right), keep a little of the same rudder in as the plane exits its pivot to prevent the way. Slowly release it on the downline.

Hope this helps.

Ken