This is the same exact problem I am having with mine. I tried putting a little E-tape around the pump head but I am getting I think to be "too good of a seal" in that it sucks the air back out on the outward stroke.
I thought that together we could solve this problem.
Here are some pictures:
Notice: the black ring was off when I opened up the gun.
Here is a picture of the pump head.
Edited by Zaxbys, 01 August 2007 - 10:46 AM.