Snider Enfield Long Rifle smoothbore

Enfield 1861 manufacture Mk II*. Enfield stock cartouche is visible with Canadian issue DC in diamond on opposite side of butt stock. Brass butt plate is regimentally marked 84 over 223. Usual proof marks on barrel and receiver including War department WD broad arrow. Most unusual thing is that this long rifle is smooth bore. Dark bore, no pitting visible. The action has been reworked with a deep “scallop” at the rear as if to fit a specific cartridge. Possibly for prison guard use? Very researchable.