I am a big fan of FSB cutout rails like the FSP rails from Daniel Defense and the Troy BattleRail Delta. I have always wished that someone would bring out a mid-length version. Apparently Troy read my mind because the Mid-Length Delta BattleRail is now available.
The Delta BattleRails are unique among free float rails because they require ZERO modifications to the rifle to install. They can be installed without removing the front sight base, hand guard cap, and delta ring assembly.
If you prefer to have a fixed front sight base like me, but also like the slim, rail-free lightweight rails that are currently en vogue, you will probably love these rails. If you are issued a rifle that you cannot modify, this could be a great solution.