Many rail systems come with that top rail integrated. The one in the pic is a CASV. Both real VLTOR ones and the clones have this rail fixed and it is not removable. Certain models of ARMS SIR come like that as well, but all have the option to remove that complete (or part of it) top rail to create a bi-level rail system.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.