Welcome to the site!

I think that once you take a look at them, you'll find that *if anything* doubles are bone-crackingly simple.
There are many different types though, and a basic tour to familiarize yourself could start with WW Greener's The Gun and it's Development.
There are many other texts, but let that be a start.

Copy this
http://books.google.com/books?id=3HMCAAAAYAAJ
then paste it in a browser destination bar.
From there, click the link on that page that will let you download the book.

Cheers
Tinker