Hello bodab. -- "I have a lee collet die in 7 mag and I CANNOT make it work. Help please, i cannot make the neck any smaller the .284, it will not hold the bullet"
Understand there is no value in putting more than maybe 20-25 pounds of pressure on the lever. At that point the neck collet has been squeezed against the inner mandrel as far as it can go. Too much more pressure can strip threads and push the aluminum top cap out of the die.
You can make the mandrell a little smaller. First, mike the diameter of the mandrel for its exact diameter. Then chuck the thing in an electric drill, put the decap pin in the chuck. Hold sandpaper to the area where the neck is formed until you have taken off ONE thousant. No more is needed or helpfull. The die should work fine then.
Or, you could anneal the necks of your brass to make them a little softer. What happens is that newer, or softer annealed cases usually get sized down fine but older cases have been worked a few times and made harder. Harder brass tends to sping back more when you size it and then it may not hold a bullet, as you are finding. Not a fault of the die, as such, it's just a fact of life when using old, work harded brass.