The one closer to the end of the barrel faces open end up. (as you described)
The second one however faces down (think upsidedown U) the space at the bottom is for that spring that you described not being able to press in all the way. (watch out, that spring is real easy to lose)
This is out of experence with the compact, but i believe they have a very similar design
http://img74.imageshack.us/img74/106/untitledzf3.jpg
^^ part 12 you put in proper, 18 you didnt?
Beyond this i cant say what would be wrong, i dont know anything beyond the compact design