I sure thought I saw grunts getting off a transport sporting AR-15s. I was surprised and though an M16 must look just like it cuz i don’t really know what an m16 looks like.
They are identical, function different on military weapons.
M16s have automatic and burst fire capability. AR-15s are semi-automatic.
M4s are similar to M16s, but barrel is shorter.
https://en.wikipedia.org/wiki/M4_carbine