Midwest Industries new QD mount for the Vortex Sparc AR gives you a lower 1/3 co -witness as well as a return to zero.
http://www.midwestindustriesinc.com/...-p/mi-qdvs.htm
http://www.midwestindustriesinc.com/...MI-QDVS-2T.jpg
http://www.ar15.com/media/mediaFiles...tyu-107644.jpg
http://www.ar15.com/media/mediaFiles...0rm-107645.jpg