Some people are all about how they look when they shoot or how they shoot their guns, I'm one of them.
Under your weapon roles would show a drop menu for the weapons you currently own under that type.
Each weapon has its own record of kills. These would still count towards the overall role.
For certain kill milestones for that specific weapon, you could unlock accessories such as sights, stocks, rail covers, horizontal/vertical grips and magazines. These are PURELY COSMETIC.
These can be