well this is not too much more complex than an AK, but this is a WWI gun and I have not seen too many people with it in their portfolio. https://en.wikipedia.org/wiki/Lewis_gun
These are fairly good as well, learned a lot from them. http://vimeo.com/35545046 http://www.3dmotive.com/training/zbrush/tileable-zbrush-video/?follow=true
You'll need to log in or register to get a higher res version but these should work. http://www.the-blueprints.com/blueprints/ww2planes/ww2-supermarine/24974/view/spitfire/