I am looking at a semi auto gun that is described as having a 11.5" upper with a 5.5 inch hider.  I don't have pics to look at but the seller says the upper has CH on the upper receiver.  It is an upper with A1 sights.

CH is a Colt marking but did Colt make any 11.5 inch uppers with attached 5.5" hiders?  

I wanted to know if somebody maybe used a Colt upper to make this or if it was a factory setup?
The upper is described as like new.

The lower is described as excellent,  not Colt but a known maker.  

Thanks for your help.