In "The Call of the Wild", why did Hal trade his gun for horsehide?

In "Call of The Wild" Buck and the other dogs had been bought by Hal and Charles.  They were on their way to Dawson and had an overloaded sled, 14 dogs and Mercedes, Charles's wife and Hal's sister.  They did not know how to prepare for the trip and the dogs were starving.  When the group reached a town called "Five Fingers" a "toothless old squaw offered to trade them a few pounds of frozen horsehide for the Colt's revolver." (pg. 72) It turned out badly though because the horsehide was fed to the dogs but gave them no nourishment.  The dogs were starving to death and the trip was taking longer than necessary because they were too weak to pull the sled.