One way to get momentum into contact on the forehand is to start opening the shoulders first as you lower the double bend and point the butt cap of the racket at the ball. By starting to open the shoulders first as you lower the double bend and supinate the hand (lay the wrist back and down a bit), it creates a stretch and open-pull dynamic similar to the serve, where one movement pulls another movement.

If you look at the forehand videos on my site, you will see this dynamic over and over again. The shoulders start to open as the wrist lays back and down. The opening shoulders will, in a sense, create a stretch and pull of the double bend. Most typically, the shoulders will be facing the net at a 45 degree angle when the butt cap of the racket points at the incoming ball.