I came across a very unique design on an M4 over a weekend combat carbine course, something that I had never seen before, a rotating picatinny rail system. Watching the student switch between accessories as fast as he was without breaking/disturbing his established shooting position was pretty interesting to see. While shooting barricades, under vehicles, etc., the picatinny rail easily rotated, allowing the student to get a better position and switch between various optics that were suitable for each situation.
In closer examination of the picatinny rail, I noted that the system consisted of 2 separate and adjustable rail systems. Both sections are composed of 4 individual Picatinny 1913 rails, which can be rotated 360 degrees, in 45 degree increments, in either direction. This rail can also be mounted to any AR style platform, a major plus. Another major plus with the system is that it maintains its zero when rotated!
Check it out at: http://ballistatactical.com/store/nautilus-rotating-rail-7-quot/dp/5