This is very similar to the Bullpump's that others have made (particularly MakeItGo), but we both felt that a write-up and public files for this type of blaster is overdue. I have other things I'm working on before this, so BLITZ going to take the leap and will follow-up with me or here if he runs into any problems.
I just did the CAD work. He is going to build the prototype and post his progress here.
Templates
http://captainslug.com/nerf/bullpump.doc
Partlist