- 12 gauge shotgun shell, of course
- First layer (and first out the barrel): double-ought buckshot, but made from iron instead of lead. The harder metal will have increased penetration (but also less spread at range, so you'll need to be a slightly better shooter -- unless you intend to saw it off) for shattering undead ribcages, and the properties of cold iron might prove useful against other beasties like fae, demons, etc.
- Second Layer: a blessed communion wafer.
- Third layer: Rosary beads made from a variety of woods reputed to be effective against the supernatural: rowan, white oak, ash, hawthorn, etc. Since most rosary beads tend to average 7mm in diameter, this quite nicely equates to #2 buckshot.
Or you could just use this beast:That's the Manville 27mm rotary launcher, originally a police riot gun manufactured in nineteen hundred and thirty-fucking-six.
PS: If you intend to fight werewolves, I suggest using Hatton cartridges, substituting silver powder for the lead or zinc.
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