I have an R6520 that I might be interested in selling.
It is a Colt Carbine, (serial number begins with CC, and is stamped COLT CARBINE) built just exactly like the Government Carbine. One exception, there are 18,000+ Government Carbines and there are only 1616 Colt Carbines, of which there are only some 300+ in the United States as they were manufactured for export.
This weapon is truly a collectors piece and is NOT a shooter. It is 99%++ condition.