Quote Originally Posted by minuteman1636 View Post
It is the same quad-rail that was used on the CR6920-EC 14.5" P/W carbines that were released recently. It is an Arms Unlimited exclusive upper receiver conversion kit currently. I don't have an explanation as to why Colt designated it "6930". The rail is a Colt proprietary product.

Additionally, to address another question in the discussion, these upper receivers are not take-offs or otherwise related to the European CR6920-EC or CR6920-EC 14.5" P/W carbine releases.
Agree, I own that Euro 14.5 and that quad rail is identical. The rest of the upper is Colt standard parts.