The Chiappa M6 is one. Most of 'em are .22 and either .410 or 20 gauge due to the light weight and recoil.
"...it's only reliable as a shotgun or rifle but not both..." The Savage M24(.223 and 20 ga.) I had was 100% reliable using either barrel. Really poor accuracy out of the rifle barrel though. Trigger was horrible and the sights worse.