Add this in the initialison line of the regarding soldier:

this addweapon "Da_MagpulAK"
this addmagazine "30Rnd_545x39_AK_7N24"

Or the standart ArmA 2 / Operation Arrowhead AK74 ammo!

The costum ammo does represent the modified version of the AK74 ammo, which is also in use today.