You're not bulletproof...

Phillips & Rogers Medusa Model 47

This rather unassuming looking revolver has a unique ability; it can chamber 25 different calibers. It does this by having a specialized cylinder with locking tabs that can adapt/conform to different sizes. Very rare and sought after. Depending on condition it can cost you around $4,000 and up.

Although it can shoot 25 different calibers, many of them are obscure and out of production. The supposed list is a lot longer but many of them are the same caliber with different names. 

9x17mm, .380 ACP, Browning Short, Corto, Kurz, Kratak
9x18mm Ultra
9x18mm Police
9x19mm Parabellum, Luger, NATO
9x20mm Browning Long
9x23mm Largo, Bayard Long
9x23mm Steyr,
9x23mm Win Mag,
9x25mm, Mauser, Export
9mm Glisenti,
9mm Rimmed,
.38 Auto, .38 ACP, 9x23mmSR
.38 Super Auto, Colt Super, 9x23mmSR +P
.38 Short Colt,
.38 Long Colt,
.38 Mid-Range,
.38 S&W, .38 S&W Corto, .380 Rimmed
.38 Special, 9x29mmR
.357 Magnum, 9x33mmR
.356 TSW