Only problem being that the M-16 is illegal for a civilian to own. You can however purchase an AR-15, which has almost exactly the same look, with the only differences being that it can't go into fully auto and it has no bayonet lug.
I own a Romanian AK-47 (semi-auto) the SVD Dragunov (also Romanian), and a single shot civilian version of the DAO-12 (its called a Streetsweeper, its just a kit so its not automatic, so its legal). And since it technically IS a weapon in BF2, I also own the K-Bar combat knife thats used in this game. (at least it looks like a K-Bar, its hard to tell, although I am fairly certain that it isn't really used much anymore.
I have fired the G3 and the L85A1, and have done simulations with the SRAW (not firing actual projectiles of course, but it was an actual launcher)