I had been wondering how the rifle stays against his back instead of swinging freely by the only strap we see on his shoulder. Between yor screencaps and the D23 pics, I can now see the leather strap with the snaps. But this tells me that it clearly is NOT a weapon he can keep drawing as quickly or as easily as he does in the show since it has to be unsnapped, first. And even assuming that after lots of snapping and unsnapping, the fasteners have become looser and easy to pop (as snaps will do over time) then he can't just drape it on his back and walk along like they keep showing. You know how hard it is snap closed a soft leather strap at that point of your back, lol? Never mind having to pull it through your cape each time.
Idk, I guess I expected a more sophisticated answer from SW than a leather strap that snaps shut.