What follows is a description of grapnel use that I posted a while back somewhere else. I just pasted the same text in here. Maybe this will be of help.
... probably the best way to use the little grapnel to set a line in an adjacent tree is in conjunction with a throwbag and line. First tie up a Prusik loop from about 40 inches of throwline or other small cordage. Girth hitch the grapnel on this loop, which will be 16 or 18 inches long. No other line is attached to the grapnel. Now, from in the first tree, throw your bag and line into the adjacent tree, over a tie in point. Lower the bag below that tie in point a few feet. Take out your grapnel on the Prusik loop and Prusik knot it onto the throwline in hand. Let the bag down, carrying the grapnel over as the line moves toward the branch it is running over. When the hanging grapnel gets close to the branch, pull the throwline back and forth a bit to get the grapnel swinging. It will snag the throwline below and on the other side of the branch. Now pull the throwline back to you and the hook will retrieve the end of the throwline with the bag to you, completing a loop around the tie in branch in the adjacent tree. Use the throwline to pull your second climbing line (or the tail of the one you are already on) over and back...tie up your hitch and transfer tree to tree. Clear as mud?
This works better than you can imagine, and allows unassisted transfers of quite some distance, much farther than you can swing the grapnel on its own line to capture a line. Of course, pay attention to the high levels of force involved on both tie in points if you don't keep the rope angles fairly low while traverseing.