Aiden Tanner / Sex Machine hands Burt the crotch pistol. Burt asks Sex Machine what the fu*k is that and he said that's the dumbest fu*king thing he ever seen. Tom Savini who plays Burt played Sex machine in the movie From Dusk Till Dawn and wore one in the movie.
The part where Seth jumps for the bullets and one land's in the chamber was thought up by D.J. Cotrona during the previous season and subsequently used in the plot of this episode.