WHAT DOES COLT 6921 FOR SALE MEAN?

Take note:  The Colt 6940 relatives of rifles are proprietary intended, with couple of user serviceable parts.  Specific equipment are required to take away the barrel nut and barrel.  The fuel procedure is unique instead of made to get replaced with mil-spec parts. Worn out rings. Tried using Colt customer service. They say it truly is out fro