As far as I am concerned, the R6550 is the cream of the crop of Colt AR15s. It's my favorite AR15 of all. Maybe it's just because one of them, an R6550K, was also my first AR15. I've never really been able to figure out why people obsess about the R6520 so much. I personally think that the "GOVERNMENT MODEL" looks a lot better than "GOVERNMENT CARBINE". At any rate, I know that there must have been at least 8,000+ R6550s produced as mine is right around that number. I'd like to find an R6650 lower receiver to use an an M4 project, too. I just don't think I could bear to be the one who parted out a complete, original R6550, though. It's almost like destroying a piece of history. Someone recently had a NIB R6550k on Tom Bower's board for $1,900.