Why is my Fi BL 12" getting hot at one ohm?

I have a D2 Fi BL and a power acoustik crypt 2200 they say you can over power the sub over what it says so we hooked it up at 1 running 1300 rms by with this amps More like 1000 rms....right now we have it at 4 running only 700 rms why is it getting so freakin hot???