Cam:
Most tankers in the 3rd ID (original part of the invasion) used M4s and kept them next to them. Some used AKs that they picked up along the way, but would still have the M4 due to the ammunition availability.
DML sells an M16 family kit that is still available in most hobby shops. There is an early version of an M4 there and should be fine. That is what I used here:
https://armorama.kitmaker.net//features/646Also, note that 3rd ID crews had AT-4s as well. They kept them near the TC hatch as well.
I don't know if tankers in OIF2 still practice this.