I would like to use some weapon names to sound familiar to readers, (AK47, M16, C4, Colt...), but as far as I have heard, using real names from weapons one must have the permission of the companies (at least, it happens with videogames).
So, my question is: Can I use real names from weapons, and not get sued due to copyright infringement?
The name of a product cannot be copyrighted it is trademarked. The appearance of the product can be copyrighted, trademarked or patented (trade dress).
Video games need additional license due to the use of the possibly copyrighted visual appearance of the weapon models. Text, which only uses the non-copyrighted names, does not.
You may need to look closer if you have extensive illustrations or are featuring the product on the cover, but the story text is almost certainly not an issue.
Use of copyrighted and/or trademarked concepts and products are allowed under Fair Use. It comes down to whether the company considers the use libelous, but that's rare, as challenging your work would give extra publicity to your statement.
Still, you can use any major brand in your work as it's simply free publicity to the brand. I've read several books mention Coke, Lucky Charms, Burger King, IHOP and even have an epic battle take place in a Walmart (and don't forget Harry Dresden's Mickey Mouse alarm clock).
The short answer is yes, it is a trademark and infringement (not copyright) is specificly exclusive right to provide products or services under said trademark.
If you're in the US, the bottom of the Wikipedia entry has links to some landmark court decisions in the field. http://en.wikipedia.org/wiki/Trademark_infringement
