Do I need to Register my Luger?

[The Worm]

So Im filling out the paperwork now, and I will hopefully be able to mail it off tomorrow. I just don't know what to fill in the blanks. Here are the questions I am having problems with:

Make: Do I put Pistole Parabellum or Luger?
Model: No idea?
Barrel Length: Seen a couple different ones, but Im not sure the exact number.

Thanks again.