In 1967 Australia and Malaya we were using the first (?) troublesome AR15's and the earliest M16's. without forward-assist and open toe flash eliminators. I can't see those types in the photo.......
But can see a few of those slippery triangular left and right handguards. Another PITA. The crunchies used to sand them with coarse sand paper to give them a better grip in the wet and monsoon weather