I recently bought a pre-ban (we still have an AWB in MA) Colt AR. The lower is marked "SPORTER MATCH HBAR". The upper is an A2 style with a 16" heavy barrel. The upper receiver, bolt, and carrier have Colt markings. However, the barrel has no markings at all. My research seems to indicate that Colt only made complete HBAR rifles with 20" barrels. Could this be a factory barrel? If so, would it be 1/7 twist? Any help would be appreciated.