Ok i took some quick flash pics to try and show how i setup my johns rifle strap, i went with what i believe was how they intended it to be, which is modern military style sling.
For reference, this is the rifle strap as it came out of the box roughly, like a normal single strap you'd sling on your shoulder:
If you adjust the strap with the plastic adjusters, you can get the style i believe is correct, since it was clearly designed to do this:
It should be noted, mine at least came with the front of the strap hooked onto the rifle's front sight, NOT the metal clip on the side of the sight, where it was supposed to be, so i unstrapped it and restrapped it in the proper place, but closeups of the positions of the straps spots:
Once the strap is setup like that, its slung over his left arm and then his head, this allows the rifle to hang naturally in a downward angle on the front of his torso, for easy access, and to be brought up in proper firing position and the strap doesn't interfere with his movements, this is the style i see in all the modern military type stuff i looked at for reference, and how i'm fairly sure it was hung in the movie itself, various views:
Hope that helps.
