WHAT DOES COLT 6921 FOR SALE MEAN?

Many thanks, however, if I go the DD MK18 route I do think I am going to commit the additional $20.00 and help AIM (and also pay OH tax).   I did Verify the G&R web-site and made an effort to include the Colt uppers to the cart and obtain the outside of stock concept.Colt has chose to increase its AR choices over and above the immediate-impingemen