Mil Spec ammo runs pretty hot, so you shoot higher then say a hunting round. Not as good quality then hunting ammo. Also, I noticed that my .308 hunting round is slower but better quality and very accurate.. The NATO/mil spec shoots about 2.5 to 3 inches higher at 100 meters and grouping can be questionable per box. The mil ammo also makes the rifle barrel really dirty in a short period of time. The NATO rounds is a third of the price though. If you are using the gun for self defense and target shooting go with mil spec. I would not use "NATO" rounds for hunting or competition. I am also too lazy to continually adjust scope between ammo.