Generally weapon in a frame stays still. Sometimes, however, there are moments where animation is necessary (e.g. reloading weapon).
At the stage of whitebox object creation it is worth to create a simple animation (mockup). The mockup of animation doesn’t have to be polished. Its only function is to check which parts of the weapon will be visible in the FPP view during the animation. It also tells us which movable parts of weapon will be visible and to what extent.