Today's movie was produced sometime in the early 1960s and describes the operation of the M16 rifle, specifically the earlier models. It also shows the functioning cycle of operation of a M16 rifle (i.e.) Firing, Unlocking, Extracting, Ejecting, Cocking, Feeding, Chambering and Locking and describes in detail how each stage works.
Note that this movie is pretty old, it actually refers to the rifle as the XM16E1. This is the first model of the M16 family that was adopted by the US Army. The earlier M16 rifle model was first adopted by the US Air Force, but the US Army insisted on a forward assist lever to be added to the rifle and therefore, the Air Force model was called M16 and the US Army version was called XM16E1 and later renamed to the M16A1 model in 1967. Also, in the early days, M16 magazines only held 20 cartridges and this can be seen in the movie as well.