Front Rail for M4

[Majestyk]

I've got a G&G CM16 Carbine and I'm looking at replacing the factory hand guard with a rail. I do like to remove the front sight assembly and get a 10/12 inch rail that could possibly fit a small lipo inside rather than having to use battery box on the outside. I'm however unsure whether the rail has to be free float or what kind of specification does it require to be able to fit on my rifle. I was looking at https://www.patrolbase.co.uk/nuprol-...ries-i?pv=8530