I was helping a group member with the identification of a Colt carbine which ended up being the Colt LT6720-R.
There are two things that make this carbine stand out. The standard carbine barrel and the Colt branded rail manufactured by Troy.
The LT6720-R appeared in the 2014 new products brochure and in the 2014 catalog. The LT6720-R did not appear in any marketing materials in 2013 or 2015.
They are not seen very often on the secondary market.