Myth: "The M16A1 is a Replacement for an M16"
I'm tired of hearing this line. An M16A1 is not a replacement for an M16. Lets look at this in more detail.
In 1964, the Air Force and Navy adopted the Colt model 604 (M16) as its standard service rifle. At that same time, the Army adopted the Colt model 603 (XM16E1) as its standard.
Both of these weapons are always identical except the 604 lacks a forward assist.
In 1967, the Colt model 603's designation was changed to M16A1. At this time, the Marines and Navy also adopted it.
At this time, some of the improvements such as chrome chambers, standard style buffers, etc were added. This is where the details are left out. Both the 604 and 603 received these new features at Colt for new production rifles.
The 604 (M16) never went out of production in 1967. It stayed in production along with the 603 until the adoption of the M16A2 by all the services.
The M16 was replaced by the M16A2, not the M16A1.
The M16 and M16A1 served concurrently just like the M4 and M4A1 do today.