Sorry if this has been addressed before. I bought a Colt (new) about 10 years ago. It has on the side of the receiver Colt MATCH TARGET Competition HBAR, Cal .223, SER CCH018XXX. Basically I bought it and kept it in storage. I have a few questions. Why don't you see Colts for sale anywhere? I have noticed at gun shows they seem to be completely missing. Same with some of the gun websites. Next, can I change out the upper receiver (w/barrel)with any brand and type? My gun does not have the flash suppressor or bayonet lug (feel naked without that ), anything else missing? Can I get an upper in .308 and drop it into this gun? I read somewhere that people were doing something like that with a .50 but it could only be shot single shot and the lower really wasn't heavy enough, would that be the same with a .308? Thanks.