But the Assault Rifle is not a G3, and the Chinese Assault Rifle is not an Ak47, or even based on an Ak47. Also, the G3 can fire 5.56mm and 7.62mm.
http://www.probertencyclopaedia.com/cgi-bin/res.pl?keyword=G3&offset=0
I beg to differ.
Here is the Assault Rifle:
http://images4.wikia.nocookie.net/fallout/images/a/a8/G3ASSAULTRIFLE.png
The Assault Rifle looks the same as a G3 rifle. It uses a G3 magazine.
Here is an early G3 with wooden stock:
http://t3.gstatic.com/images?q=tbn:GSNjEgbbW3cmnM:http://img.photobucket.com/albums/v130/montereyjack/10b8bcd6.jpg&t=1
The HK33 fires 5.56, but the Assault Rifle in Fallout 3 is not that weapon.
Here is an HK 33. It uses a different and longer magazine, because the G3 magazines only take 20 bullets
http://t0.gstatic.com/images?q=tbn:DDAM0tqrY0K4CM:http://world.guns.ru/assault/hk33.jpg&t=1
It would be ridiculous to say they are not based on real weapons. They may not be the same in game, but the game sure as hell borrowed the design.
That's why, when you are promised a Tommy-gun in Fallout New Vegas, we know it'll most probably be based on the real gun, but there could very well be some slight differences from the real one.
Edit: The G3 can not fire 5.56. HK made some weapons for different calibers.
HK G3 = 7.62
HK 33 = 5.56
HK MP5 = 9mm
They are all the same design, but in different scales. An mp5 is like a G3, only in smaller scale. It uses the same mechanics. Trust me, I know how to pick both weapons apart and put them together again.