Wow, great tutorial, I had no idea floating geometry could be used like that. It shows that I didnt know how to use floating geometry. Seems I was making things way more complicated than they needed to be, and now I am no longer stuck! Thank you metalliandy!
Yes, a floater is just floating over the mesh, if it's an inset hole, you have to float it far enough away it doesn't penetrate the base mesh. Also it's a good idea to keep floaters pretty shallow, you can make something look like a hole without it being very deep.
What is the purpose of your model, what end use will it have (video game/render?)? If you model it for a video game I would add those in as floating geometry if it's not a for a first person shooter. If you don't want floating geometry, you can use a boolean for the forward assist. You can also use booleans for the brass…
Floating geometry might also be the answer. http://www.iddevnet.com/quake4/ArtReference_CreatingModels (see the screenshots at the end of the "Modeling Your Character" section)
You will probably want to at least add an extra cut where the bottom of that extrusion meets the hood. You may need another one along the segment that connects the edge of the hood to the scoop. You could also float this detail and pull the edges out a little (the open edges where it floats above the hood) so that it…