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.
"Even thinking of that video of the chick loading the musket makes my penis sad."
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.
Dude were you and nancy loading the musket last night? We could smell it in the other room.