WTK Information pertaining to a Colt AR series model, stamped "Carbine" and serial number prefix "CC". Interested to know how many made, interesting collector information on this particular model and any other relevant knowledge. Haven't heard or seen much if any on this particular model.
Also how many different configurations were there and collector value on complete rifle/ and or lower itself.
There is a thread around here about Colt 6520, maybe you could ask the author team member Ekie if he have any info about it.
Colt Govt Carbine 6520 Data Base thread link
Here's also a link about Colt serial number prefix, models and pre-ban/ post-ban info.
Biggerhammer.net's Colt Serial Number List and FAQ website link
Here's a picture thread of rollmarks and markings of Colt and also other brands.
Lower Receiver & Mag Floorplate Rollmarks, Logos and Markings thread link
As for value take a look at some sites like GunsAmerica.com, GunBroker.com and others in the internet.
I used to have a Colt transitional model R6420 AR-15 Sporter II carbine, 16" 1/7 A2 barrel, furniture are A2 except A1 sights & A1 slab side lower.
It seems that your Colt Carbine model R6520 was made after my Sporter II carbine and before the Gov't Model Carbine probably for only several years and because of the low production quantity makes it a rare and collectable model (just my opinion).