Quoted:
Watching the BCM KMR installation video on Youtube, I noticed that the barrel nut, then gas block, goes on, and then the rail. I have a low profile gas block that is predrilled, and has a taper pin, and a set screw at the bottom making it seemlngly impossible to install it all after the rail goes on like the URX4 from KAC does.

Any other FF rails, keymod, or otherwise that go one like BCM?