It looks like a 14.5" carbine (or a 10" or 11.5" with the long moderator) with a fixed carry handle and a single heat shield, pre-M4 handguard, which, going by Colt model numbers for simplicity, only really narrows it down to almost any carbine between the Colt 609 and 727, or a clone build on some other lower. The vague umbrella term "CAR-15" is as specific as I'd really get with this without any more drawn detail to distinguish between different models.
