To get the most accuracy out of it, I would look for match grade ammo like Hornady 55 gr VMAX, Hornady 75gr Match , Federal Gold Metal Match 69 or Black Hills 77 gr SMK. All of the above ammo should be sub-MOA, where as your m193 and m855 will be 2-4".
Ive had very good results with the 55 gr VMax in my Ultra Match