My Department just bought about a dozen or so new R6721 AR15A3 Tactical Carbines. I have one of my own I got about 2 years ago and the new ones have a few signifigant changes, for anyone caring to know.
First thing is the collapsible stock is that new style slider with the larger buttplate, longer length and fixed swivel on the bottom. Its still 4 position.
The front pivot pin is a milspec push type, not a screw type.
The chambers are definitely chrome lined, but it didnt appear the bores were. I was only able to look at the muzzle end through the flash suppressor for a few seconds but it didnt appear to have the chrome ring around the end of the barrel like the chrome lined ones have. I am not positive on this though.
The entire rifle is finished black, not just the aluminum parts. Even the barrel is now black oxide finish and not the gray parkerizing like Colt has done in the past.
My 2 year old model has the older style stock slider, small diameter front pivot pin that has a screw on the left side and chrome lined bore and chamber. The upper and lower receiver, carry handle and front sight base are all finished in black with the barrel and mag catch in gray parkerizing.