To expand on what Rob said.
The powertube spacers adjust the point where the bolt no longer seals the dump chamber, allowing you to adjust the fireing point in relation to the on/off actuation.
__________________ FeedBack FS: Triggers/Sears FS: Pumps
Originally Posted by Marauder_Pilot
It will eventually get to the point where you're living in the back of a '78 Oldsmobile with a trunk full of the finest paintball gear known to man.