Catch and release. Colt A2-ish carbine upper. Was told it was a complete Colt upper, but this turned out to be false -- the upper is Colt CM marked and BCG is C marked, but the barrel is truly a mystery. Unmarked 16", heavy profile under the handguards but 0.625" at the FSB and pencil profile afterwards -- can't find anything on it online but rifling is in good condition and appears to be chrome. Complete upper with CH, BCG, and skinny handguards.