First Person Weapon

I've gotten a custom mesh into the starter.fps demo and I've noticed something. The eye node dictates the height or position the character is veiwing from in fps mode. The crossbow is always present nomatter where you set this, which tells me that it is loaded seperately. Can someone explain to me how this works? I basically want to set up a situation where I have a set of custom highres arms animating with the weapon when viewed from the players perspective. Logically I'd just make these arms part of the weapon that is viewed from first person, but I don't understand where and how it loads this. I'm not a coder so please excuse my ignorance. I'm in charge of all the art and animations on this project we're working on so I need to figure this stuff out before I can decide how I'm going to tackle this problem.