I've been working on this for a long time. The feeling that has worked best for me: For a righty, feel that the right forearm is vertical at P4 (top of the back swing). When I'm working on this at the range, I imagine the distant target (flag stick). When I swing, I imagine my right forearm getting vertical and parallel with the flag stick. Then, in the transition into the down swing, feel that your right arm skips a flat rock (side arm) across a pond.
Over the past month, I'd struggled again some with the transition. New feelings are working better. Smooth back swing (like Snead) with a fluid big hip turn, then at the top palmar flex with the leading wrist and push down with the leading arm (same direction as palmar flexion) while at the same time squeezing the trailing elbow (right elbow for a righty)in and forward imagining it going in front of the belly button. When I make a nice big fluid centered hip turn the move is easy, when I get "tight" and restrict my hip turn, it's more difficult.