Get some (old) 357 brass and drill out flash hole and load parifin wax over mag primer...tough on rodents and flying rats in barns!
Back in the heyday of the TV westerns in the 1960s fast draw clubs sprang up all over the country.
My dad was HEAVILY involved in one.
They shot 45 Colts with parafin bullets propelled by a shotgun primer.
I've probably got about 1000 cases he drilled the primer pockets out of to accept the shotgun primers.
They scoot wax bullets along at about 800 fps.