I have the carbine-length ARMS SIR #50 (civ version that does not require gunsmithing), and am in the market for a full-length rail system for the C7 as well (two-piece, one-for-one replacement, non-permanent). Two options for me: DD Omega Rail 12.0 or Midwest Industries MCTAR-19 (full lenght two-piece). $100.00 difference, the choice is clear in my mind. The ARMS SIR system is way overpriced and had I done more research back then, I may have chosen something different for the carbine. Solid, no-frills construction though, and while non-permanent, does install almost free-float-like.