I can't believe that no one has heard this before:

Actually it came from Mortie. He was busy shooting squill out of his trailer's window using the dining room table as a shooting bench, and he was drinking moonshine and set the place on fire, when he accidently breathed on a surplus tracer round.

Then as the place went up, all of his loaded ammo and all the open cannisters of powder he had laying around the place, and all of the bullets he had went off. The trailer was burning like a torch and shooting off ammo in all sorts of directions.

Of course the two mule fire department refused to get near it to try to put it out. The Fire Chief told Mortie that he was not going to get near anything that was shooting " like that house a fire".

So shooting like " mortie's house a fire" sort of spread as a term.. However since no one knew who Mortie was, or those that did, did not give a shit, the Mortie was dropped by the phrase.

It is gospel, heard it on "Little Known Facts" on the radio this past Monday morning.

seafire

This is just a guess too, but I'd think it came from all the crackling and popping and explosions associated with a raging house fire.