In The Story of Yue, the origin of this gun is described as follows: "(Yue Fei) went out of the temple gate and turned to the back. I saw a wisp of flowing spring in the middle of the mountain, and a big stone next to it was engraved with the words' Liquan Qipin', but it was Su Dongpo's handwriting. There was a cave in the spring, but there was a big snake head sticking out of the hole. His eyes were radiant, and saliva flowed out of his mouth and dripped into the spring. Yue Fei thought,' What good is this evil animal's mouth? Dropped in water, how to use it? Wait till I kill him.' He put down the tea bowl, picked up a big stone, and looked at the snake head with kindness. If you don't fight, you can still fight. This time, it is neither biased nor crooked, just hitting the snake head. I only heard the sound of "shout", and in an instant, the stars and fog were misty. The snake's two eyes showed golden light and opened its mouth like a blood basin, looking at Yue Fei's face. Yue Fei hurriedly put his body on one side, let the snake head pass, and took advantage of the situation to delay the tail of the snake; There was a loud sound, and when you looked intently again, there was a snake tail in your hand, but it was a golden gun with the words' Liquan Spear' on its handle. Looking back, the spring water has dried up without a drop.
—— See the fourth episode of The Legend of Yue, The Little Hero of Qilin Village Jieyi Liquan Cave and the Old basilisk Offering a Gun.