The only problem is that the tension from the spring is likely to keep the lead dart in place, rather than allow it to drop in to the barrel. Perhaps if there was a ramp at the end, which would force the darts down as the spring pushes them forward? Or, you could make it a more positive movement by adding a little trough (like a half pipe of brass) with a peg that sticks through the top pipe, and is spring loaded to keep it pressed out. Then, have a mechanism attached to the pump handle that pushes the peg in and kick the dart in to the open barrel. This is a good idea! I may have to build one!
EDIT: Hahaha! I totally missed Rokor's post.
Edited by Draconis, 22 January 2009 - 07:52 PM.