Bill shot his load way to early.
Just an FYI, but I believe the phrase you're searching for is "shot his wad."
Civil war era rifles were loaded with gunpowder, and then a stopper (which was a wad), and then a bullet. Shooting one's wad meant to activate the firing mechanism and destroy the wad with no bullet in place, which would then lead to the soldier needing to start the process over again.
It has been modernized in the sense that people now associate it with a gambler betting too big too soon at the table, and losing his "wad" of cash by "shooting" craps.
"Shot his load" refers to nothing other than ejaculation.