Factual error: This is set in 1966. The soldiers are all using the Aussie version of the M16 which was introduced in Vietnam by their military in 1967 with limited use and only became more widely used somewhat later.
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Suggested correction: There's no such thing as an Aussie version of the M16, they were all made in the USA by Colt, or its contractors. I assume the poster means the M16A1, identifiable by the bolt assist lug on the right hand side and closed flash suppressor.