Casting is throwing the clubhead away from the top, so the angle between your lead arm and the shaft disappears long before impact. The energy you built goes into the air rather than into the ball.
Why holding the angle does not work
Lag is not something you hold. It is something that happens when the body leads and the club follows. Try to hold it manually and you get tension, a stalled body, and usually a block or a hook.
If your sequence is wrong, lag cannot survive. If your sequence is right, lag appears without being managed.
The two causes worth your time
Starting down with the hands and shoulders
If the upper body fires first, the only thing left to do is throw the club. The fix is starting down with pressure moving into the lead foot while the club still feels like it is going back.
Disconnected arms
Arms held away from the body have to generate speed themselves, and the way arms generate speed is by throwing. Reconnect them and the body becomes the engine.
Drills
- Pump drill. Go to the top, pump down to waist height three times keeping the club behind your hands, then hit. Slowly.
- Feet together. Removes the option of lunging and forces sequence.
- Step drill. Start with feet together and step the lead foot out as you start down. Teaches pressure shift before rotation.
A test you can run weekly
Make a swing and stop at hip height coming down. Where is the clubhead? If it is already level with your hands, you cast. If it still trails behind, your sequence is working.
Speed comes last. Get the order right at half pace, or you are simply practising the cast faster.