First thing I would do is patent the idea. Then, depending on whether it is a complete weapon or a modification to an existing weapon, I would shop the idea around with a manufacturer who produces similar weapon types. In other words if it is a completely new military type carbine, I would contact FN, Colt, Bushy etc. Also, to protect yourself in the case of an idea for a weapons system, and not an actual prototype, you can have any firearms mfg's in which you reveal your system details to, sign a non disclosure agreement. I got that last idea from shaggy when I asked him for advice on my sisters new product ideas for another business. Another very good resource is right here, we have a few guys on board here in the firearms biz like Shawn from Cavalry Arms and Tim(antiUSSA) from Castle Arms and Kurts Kustom who can be of great assistance if anyone has a potential product.