The reason you have this issue is that your bolt mesh is weighted at 1 in two vertex groups: weapon and bolt:
Remove it from the weapon vertex group and problem solved. To do this, you can ↹ Tab into Edit Mode, hit L while hovering the bone mesh to select it, then in the Vertex Groups panel, select the weapon group and hit the Remove button.
On a different note: Keeping things simple is always preferable: fewer factors for issues, faster to use, edit and maintain, ... In that regard:
You do NOT need to make multiple armature deform modifiers with specific groups. One armature modifier with just the vertex groups checkbox enabled is more than enough.
You also should have a root bone at the top of the bone hierarchy, especially if you export outside of Blender where some exchange formats and software might give you trouble for not having one.
You do not need Child Of constraints on the weapon parts bones to parent them to a bone that could already be a parent in the first place. These kind of constraint are not for replacing a hierarchy, their purpose is to give alternative when needed. Instead, parent these bones to the weapon bone, and use Child Of constraints to parent these bones to external things, like hands, only when needed.