I remember reading an article about 20 years that the supplied a little over 750,000 M16rifles of all versions to the South Vietnamese government. After being seized by the "new" Vietnamese government, the new "owners" also used them in their conflict with Cambodia. I also remember seeing another article that the US Government seized a ship load of M16 rifles that the Vietnamese government was trying to sale on the arms market. The US Government considers all weapons provided as aid as still as US Government property. I also remember that a large numbers showed up in El Salvador and Nicaragua rebel caches after having been smuggled from Fidel in Cuba. The serial numbers had been obliterated. Recently the Vietnamese government had been re-manufacturing a number into shorty type M16 rifles.
Believe or not this number only represents a mire fraction of the M16 rifles produced.