Another name for Kids in Sandbox, the sexual practice of ramming a foreign object into a man's penis for sexual pleasure. Named so for the way a musket is loaded by ramming the shot and gunpowder down the barrel, before rifles and magazines came into play.
When a male inserts his fecal matter into a woman's butthole and then forces it in deeper with his penis. The woman will then push as hard as she can and shoot it out.