Top to Bottom, clones of: Early M16, Mid M16A1, M16A2. The slings show a progression too, from Garand type cotton M1 to the "seatbelt" nylon M1 to the black nylon M1. It's amusing to an extent that they are ALL "Sling, M1" but though the materials change, the part number doesn't. They're a use until expended and replace with whatever supply sends.
These are the USGI issued M16's with iron sights. I tend not to count the M16A3 because it's a selector difference from the M16A2. The M16A4 is the flat-top and thus ended the iron-sight era in the US Marine
They are an interesting progression of vintage content as well. Charlotte, the M16 is nearly entirely vintage with the exception of the lower receiver and fire control group. Tabitha, the M16A1 has vintage furniture, upper receiver and flash-hider. Andrea, the M16A2 is entirely new construction.