I have encountered this problem with the De Walt equivalent. Three possible solutions:
WD40 may release it but carries the risk of making any dust causing it to stick forming a paste and drying solid.
Put the chuck into a vice, hold the drill tight and pull the trigger. This uses the drill's own power to force it to close (if jammed closed, do this with the reverse).
If the drill has a separate locking ring, put a "boa constrictor" wrench round each and turn them in opposite directions. If the drill is pointing away from you then the chuck goes anticlockwise and the locking ring (which is will be nearer to you) goes clockwise, Once it has moved a bit, you can move on the using the vice and send it both ways a few times to clear it out.
Peter 47820, March 2008
