Question on Daniel Defense RIS II

[mtang45]

I picked up a like new RIS that was a new rifle take off, and am trying to install it on my carbine. The problem is the end piece that is held in place by the DD barrel nut is very loose. No instructions were included so I'm assuming I have all the pieces and am installing correctly. Anyone have experience with the RIS that can shed some light on what may be wrong?

Thanks