The venerable iron sights on the M-16 are going away in the USMC, in favour of the red dot. They will keep training using an attachable mini iron sight (for when the red dot goes dead), but it's days are numbered. They're also going in favour of a two point sling and they'll be training in meters, rather than yards, on the range.
Marines ditch iron sights, consider new marksmanship training tables
Marines ditch iron sights, consider new marksmanship training tables