Cig smoke sticks around a long time... this may be an odd suggestion. If cleaning doesnt work id go to the mall and pick my favorite flavor of incent and stick the gun and the incense in a closet. Or shed outside or garage cabnet. Wherever you wont mind the smell. And smoke that gun out! Light like 10 incents. You have to fight the decades of smoke marination in one go. So make it hazy.
Or you could just hit it with some febreeze wipes right before you shoot