HYDRA MATICS are rare and most are Vietnam Vintage. The COLTS too are mostly from Vietnam.
That is why some prefer the ELISCO version, manufactured under licensed from COLT. Because it is newer. Way back 1978 The Philippine Government issued M-16s to the Army, to be manufactured here, under licensed. So all machineries, forgings and tools are imported only the labor, electricity and water are local.
But of course you dont have the COLT logo!! only the stamping "UNDER LICENSED BY COLT".
They stopped manufacturing in sometime 1985.
On long firearms, the one that you can legally purchase at a gun store is a .22 long rifle or shotgun(pump or semi-auto). 5.56 caliber rifle as well as 9mm sub-gun can only be licensed if there is an "amnesty" for unregistered FA. You can register it no questions asked. Most M-16s that went to civilian hands are from insurgents that captured this from combat and sometimes sell this(if they dont need it)to gun collectors and enthusiasts.