The final barrier was of molten rock at the heart of the volcano. Then the man took out his pistol. The fell troll laughed. It is known that metal, especially worked metal, quenches fire. That is why so many technologies fail in the elf lands where magical rules reign.
Metal wires quench the electrical fire.
Metal guns quench the explosive fire of the bullets in them. So gunpowder works, and makes the best of fireworks and rockets, but guns do not. Except this gun had no metal in it, and the cocobolo wood was poison to the troll, so as each bullet struck, he did not regenerate to heal from it. Seven bullets struck the fell troll and its power slipped from it. So it dropped the fire walls about it and came at the man, and he took his sword and met it in a passing attack.