I just purchased a 15 inch c/f rail with the 2 inch front sight rail from Lancer after seeing it at shot show. It feels about the same diameter as the JP Vtac, but has a greater CDI factor. It is a little longer than 16 inches when mounted, so it won't work on a 16 inch barrel. To be honest with you, I really prefer the 15 inch Troy TRX rail, I've been running on one of my other rifles. I feel like I can get a better hold of it. If you can, try to get a hold of a rail that your considering and see how it feel on a rifle, most people are happy to let you shoot their rifles after the matches.
Good Luck,
JG