In the part where Arnold is firing the M-60 machine gun, he fires about 200 rounds or so from the probably 80 round chain, then all of a sudden the belt becomes a 30 round chain. And then a few seconds later, he turns to blow some more guys away and the belt has about 100 rounds on it.
in the same scenes he not only has a magic belt of ammo that keeps regenerating, the belt of ammo also feeds from both sides. from the left in one scene, from the right in the next scene, back to the left in the next scene
The shots where the ammo belt is on the wrong side are probable flipped. I have no idea why directors flip shots, but you see it all the time in movies.