I've never seen one mounted that far either. You would need some major eye relief in your optics (similiar to pistol scopes) for that to even be possible. Also, if you wanted to mount it on the barrel wouldn't a cantilever barrel be a better choice. I'm not a fan of the cantilever, just seems to me it would be a better choice than mounting it in the middle of the barrel. I bought a browning A-bolt 12 guage slug gun so my scope is mounted on my receiver. My prior slug gun which I use as a backup is an 870 with a slug barrel, it just has that plate that mounts to the side of the receiver once you remove the pins.