It has happened a few times in history, e.g. the French revolution and the Bolshevik revolution.

However once they killed the "elite" or "oppressor" they couldn't stop the killing, and kept redefining who the "oppressor" was, until it was anyone who had one more cow than the rest.

Those are not good examples. OP is asking about things like military coups, where the seizure of power comes from within the existing establishment.